The ameliorative role of 28-homobrassinolide under chilling stress in various growth, photosynthesis, enzymes and biochemical parameters of cucumber (Cucumis sativus L.) were investigated. Cucumber seedlings were sprayed with 0 (control), 10-8, or 10-6 M of 28-homobrassinolide at the 30-day stage. 48 h after treatment plants were exposed for 18 h to chilling temperature (10/8°C, 5/3°C). The most evident effect of chilling stress was the marked reduction in plant growth, chlorophyll (Chl) content, and net photosynthetic rate, efficiency of photosystem II and activities of nitrate reductase and carbonic anhydrase. Moreover, the activities of antioxidant enzymes; catalase (E.C. 1.11.1.6), peroxidase (E.C.1.11.1.7), superoxide dismutase (E.C. 1.15.1.1) along with the proline content in leaves of the cucumber seedlings increased in proportion to chilling temperature. The stressed seedlings of cucumber pretreated with 28-homobrassinolide maintained a higher value of antioxidant enzymes and proline content over the control suggesting the protective mechanism against the ill-effect caused by chilling stress might be operative through an improved antioxidant system. Furthermore, the protective role of
28-homobrassinolide was reflected in improved growth, water relations, photosynthesis and maximum quantum yield of photosystem II both in the presence and absence of chilling stress. and Q. Fariduddin ... [et al.].
To determine the photosynthetic characteristics of C3 plants and their sensitivity to CO2 at different altitudes on the Tibetan Plateau, hulless barley (Hordeum vulgare L. ssp. vulgare) was grown at altitudes of 4,333 m and 3,688 m. Using gas-exchange measurements, photosynthetic parameters were simulated, including the maximum net photosynthesis (Pmax) and the apparent quantum efficiency (α). Plants growing at higher altitude had higher net photosynthetic rates (PN), photosynthesis parameters (Pmax and α) and sensitivities to CO2 enhancement than plants growing at lower altitude on the Tibetan Plateau. The enhancements of PN, Pmax, and α for plants growing at higher altitude, corresponding with 10 μmol(CO2) mol-1 increments, were approximately 0.20∼0.45%, 0.05∼0.20% and 0.12∼0.36% greater, respectively, than for plants growing at lower altitude, respectively, where CO2 levels rose from 10 to 170 μmol(CO2) mol-1. Therefore, on the Tibetan Plateau, the changes in the photosynthetic capacities and the photosynthetic sensitivities to CO2 observed in the C3 plants grown above 3,688 m are likely to increase with altitude despite the decreasing CO2 partial pressure. and Y. Z. Fan ... [et al.].
Yellow-green foliage cultivars of four vegetables grown outdoors, i.e., Chinese mustard (Brassica rapa), Chinese kale (Brassica oleracea var. alboglabra), sweet potato (Ipomoea batatas) and Chinese amaranth (Amaranthus tricolor), had lower chlorophyll (Chl) (a+b) (29-36% of green cultivars of the same species), total carotenoids (46-62%) and ascorbate (72-90%) contents per leaf area. Furthermore, yellow-green cultivars had smaller photosystem II (PSII) antenna size (65-70%) and lower photosynthetic capacity (52-63%), but higher Chl a/b (107-156%) and from low (60%) to high (129%) ratios of de-epoxidized xanthophyll cycle pigments per Chl a content. Potential quantum efficiency of PSII (Fv/Fm) of all overnight dark-adapted leaves was ca. 0.8, with no significant difference between yellow-green and green cultivars of the same species. However, yellow-green cultivars displayed a higher degree of photoinhibition (lower Fv/Fm after illumination) when they were exposed to high irradiance. Although vegetables used in this study are of either temperate or tropical origin and include both C3 and C4 plants, data from all cultivars combined revealed that Fv/Fm after illumination still showed a significant positive linear regression with xanthophyll cycledependent energy quenching (qE) and a negative linear regression with photoinhibitory quenching (qI). Fv/Fm was, however, not correlated with nonphotochemical quenching (NPQ). Yet, a higher degree of photoinhibition in yellow-green cultivars could recover during the night darkness period, suggesting that the repair of PSII in yellow-green cultivars would allow them to grow normally in the field. and J.-H. Weng ... [et al.].
A modified exponential model was used to describe light-response curves of Nicotiana tabacum L. The accuracies of an exponential model, a nonrectangular hyperbola model, a rectangular hyperbola model, a modified rectangular hyperbola model and the modified exponential model were evaluated by Mean square error (MSE) and Mean absolute error (MAE). The tests MSE and MAE of the modified exponential model were the lowest among the five models. The light saturation point (LSP) obtained by the exponential model, the nonrectangular hyperbola model and the rectangular hyperbola model were much lower than the measured values, and the maximum net photosynthetic rates (Pmax) calculated from these models, were greater than the measured values. Pmax at LSP of 1,077 μmol m-2 s-1 calculated by the modified exponential model was 12.34 μmol(CO2) m-2 s-1, which was more accurate than the values obtained from the modified rectangular hyperbola model. The results show that the modified exponential model is superior to other models for describing light-response curves. and Z. Y. Chen ... [et al.].
The transfer of light energy from phycobilisomes (PBS) to photosystem II (PSII) reaction centers is vital for photosynthesis in cyanobacteria and red algae. To investigate the relationship between PBS and PSII and to optimize the energy transfer efficiency from PBS to PSII, isolation of the PBS-PSII supercomplex is necessary. SPC (sucrose/phosphate/citrate) is a conventional buffer for isolating PBS-PSII supercomplex in cyanobacteria. However, the energy transfer occurring in the supercomplex is poor. Here, we developed a new buffer named SGB by adding 1M glycinebetaine and additional sucrose to SPC buffer. Compared to SPC, the newly developed SGB buffer greatly enhanced the associated populations of PBS with thylakoid membranes and PSII and further improved the energy transfer efficiency from PBS to PSII reaction centers in cyanobacteria in vitro. Therefore, we conclude that SGB is an excellent buffer for isolating the PBS-PSII supercomplex and for enhancing the energy transfer efficiency from PBS to PSII reaction centers in cyanobacteria in vitro., L. P. Chen, Q. X. Wang, W. M. Ma., and Obsahuje bibliografii
Measurement of leaf area is commonly used in many horticultural research experiments, but it is generally destructive, requiring leaves to be removed for measurement. Determining the individual leaf area (LA) of bedding plants like pot marigold (Calendula officinalis L.), dahlia (Dahlia pinnata), sweet William (Dianthus barbatus L.), geranium (Pelargonium × hortorum), petunia (Petunia × hybrida), and pansy (Viola wittrockiana) involves measurements of leaf parameters such as length (L) and width (W) or some combinations of these parameters. Two experiments were carried out during spring 2010 (on two pot marigold, four dahlia, three sweet William, four geranium, three petunia, and three pansy cultivars) and summer 2010 (on one cultivar per species) under greenhouse conditions to test whether a model could be developed to estimate LA of bedding plants across cultivars. Regression analysis of LA versus L and W revealed several models that could be used for estimating the area of individual bedding plants leaves. A linear model having LW as the independent variable provided the most accurate estimate (highest R2, smallest mean square error, and the smallest predicted residual error sum of squares) of LA in all bedding plants. Validation of the model having LW of leaves measured in the summer 2010 experiment coming from other cultivars of bedding plants showed that the correlation between calculated and measured bedding plants leaf areas was very high. Therefore, these allometric models could be considered simple and useful tools in many experimental comparisons without the use of any expensive instruments. and F. Giuffrida ... [et al.].
We have developed a simple and an effective method for the isolation of photochemically active broken chloroplasts from conifer needles that can be applied for a wide variety of conifer species with needle-like leaves. The utilisation of this method in photosynthetic studies offers a possibility to examine the efficiency of almost any component of thylakoid electron-transport chain and to disclose information about individual parts of primary photosynthetic processes that would be otherwise difficult to obtain. Various aspects influencing the outcome of this procedure, including the amount of needles necessary for sufficient yields, the possible length and the conditions of their storage, the best method for their disruption, the composition and pH of isolation and storage buffers, the centrifugation sequence, etc., are discussed., D. Holá ... [et al.]., and Obsahuje bibliografii
a1_The aim of this work was to study the acclimation of photosynthesis in a boreal grass (Phalaris arundinacea L.) grown in controlled environment chambers under elevated temperature (ambient + 3.5°C) and CO2 (700 μmol mol-1) with varying soil water regimes. More specifically, we studied, during two development stages (early: heading; late: florescence completed), how the temperature response of light-saturated net photosynthetic rate
(Psat), maximum rate of ribulose-1,5-bisphosphate carboxylase/oxygenase activity (Vcmax) and potential rate of electron transport (Jmax) acclimatized to the changed environment. During the early growing period, we found a greater temperature-induced enhancement of Psat at higher measurement temperatures, which disappeared during the late stage. Under elevated growth temperature, Vcmax and Jmax at lower measurement temperatures (5-15°C) were lower than those under ambient growth temperature during the early period. When the measurements were done at 20-30°C, the situation was the opposite. During the late growing period, Vcmax and Jmax under elevated growth temperature were consistently lower across measurement temperatures. CO2 enrichment significantly increased Psat with higher intercellular CO2 compared to ambient CO2 treatment, however, elevated CO2 slightly decreased Vcmax and Jmax across measurement temperatures, probably due to down-regulation acclimation. For two growing periods, soil water availability affected the variation in photosynthesis and biochemical parameters much more than climatic treatment did. Over two growing periods, Vcmax and Jmax were on average 36.4 and 30.6%, respectively, lower with low water availability compared to high water availability across measurement temperatures. During the late growing period, elevated growth temperature further reduced the photosynthesis under low water availability., a2_Vcmax and Jmax declined along with the decrease in nitrogen content of leaves as growing period progressed, regardless of climatic treatment and water regime. We suggest that, for grass species, seasonal acclimation of the photosynthetic parameters under varying environmental conditions needed to be identified to fairly estimate the whole-life photosynthesis., Z.-M. Ge ... [et al.]., Obsahuje poznámky, and Obsahuje bibliografii
Winter wheat is a grass species widely planted in northern and central China, where the increase of aerosols, air pollutants and population density are causing significant reduction in solar irradiance. In order to investigate the adaptation of winter wheat (Triticum aestivum L., cv. Yangmai 13) to low irradiance conditions occurring in the downstream plain of the Yangtze River (China), plants were subjected to four solar irradiance treatments (100%, 60%, 40%, and 20% of environmental incident solar irradiance). Significant increases in chlorophyll (Chl) and xanthophyll (Xan) pigments, and decreases in Chl a/b and Xan/Chl ratios were observed in plants under low light. Light-response curves showed higher net photosynthetic rates (PN) in fully irradiated plants, that also showed a higher light-compensation point. Shaded plants maintained high values of minimal fluorescence of dark-adapted state (F0) and maximum quantum efficiency of PSII photochemistry (Fv/Fm) that assess a lower degree of photoinhibition under low light. Reduced irradiance caused decreases in effective quantum yield of PSII photochemistry (ΦPSII), electron transport rate (ETR), and nonphotochemical quenching coefficient (qN), and the promotion of excitation pressure of PSII (1 - qP). The activities of the antioxidant enzymes superoxide dismutase and peroxidase were high under reduced light whereas no light-dependent changes in catalase activity were observed. Thiobarbituric acid reactive species content and electrolyte leakage decreased under shaded plants that showed a lower photooxidative damage. The results suggest that winter wheat cv. Yangmai 13 is able to maintain a high photosynthetic efficiency under reduced solar irradiance and acclimates well to shading tolerance. The photosynthetic and antioxidant responses of winter wheat to low light levels could be important for winter wheat cultivation and productivity. and Y. Zheng ... [et al.].
In this article, the effects of increased light intensities on antioxidant metabolism during ex vitro establishment of Ulmus minor micropropagated plants are investigated. Three month old in vitro plants were acclimatized to ex vitro conditions in a climate chamber with two different light intensities, 200 μmol m-2 s-1 (high light, HL) and 100 μmol m-2 s-1 (low light, LL) during 40 days. Immediately after ex vitro transfer, the increase of both malondialdehyde (MDA) and electrolyte leakage in persistent leaves is indicative of oxidative stress. As the acclimatization continues, an upregulation of the superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) enzyme activities were also observed. Simultaneously, MDA content and membrane permeability stabilized, suggesting that the antioxidant enzymes decrease the deleterious effects of reactive oxygen species (ROS) generation. Unexpectedly, newly formed leaves presented a different pattern of antioxidative profile, with high levels of MDA and membrane leakage and low antioxidant enzyme activity. Despite these differences, both leaf types looked healthy (e.g. greenish, with no necrotic spots) during the whole acclimatization period. The results indicate that micropropagated U. minor plantlets develop an antioxidant enzyme system after ex vitro transfer and that, in general, LL treatment leads to lower oxidative stress. Moreover, new leaves tolerate higher levels of ROS without the need to activate the antioxidative pathway, which suggests that the environment at which leaves are exposed during its formation determinate their ability to tolerate ROS. and M. C. Dias, G. Pinto, C. Santos.
The activity of enzymes characteristic for C4-type photosynthesis was determined in different organs of two herbaceous plants: Reynoutria japonica Houtt. and Helianthus tuberosus L. The activity of phosphoenolpyruvate carboxylase (PEPC) was usually higher in the roots, some of the stem tissues and petioles in comparison to the leaf blades. The highest activity of malic enzymes (NAD-ME, NADP-ME) and phosphoenolpyruvate carboxykinase (PEPCK) was in the petioles and stem tissues of both plants and the lowest in the leaf blades and the pith of Helianthus tuberosus L. and M. Kocurek, J. Pilarski.
Leaf area estimation is an important biometrical observation recorded for evaluating plant growth in field and pot experiments. In this study, conducted in 2009, a leaf area estimation model was developed for aromatic crop clary sage (Salvia sclarea L.), using linear measurements of leaf length (L) and maximum width (W). Leaves from four genotypes of clary sage, collected at different stages, were used to develop the model. The actual leaf area (LA) and leaf dimensions were measured with a Laser Area meter. Different combinations of prediction equations were obtained from L, W, product of LW and dry mass of leaves (DM) to create linear (y = a + bx), quadratic (y = a + bx + cx2), exponential (y = aebx), logarithmic (y = a + bLnx), and power models (y = axb) for each genotype. Data for all four genotypes were pooled and compared with earlier models by graphical procedures and statistical measures viz. Mean Square Error (MSE) and Prediction Sum of Squares (PRESS). A linear model having LW as the independent variables (y = -3.4444 + 0.729 LW) provided the most accurate estimate (R 2 = 0.99, MSE = 50.05, PRESS = 12.51) of clary sage leaf area. Validation of the regression model using the data from another experiment showed that the correlation between measured and predicted values was very high (R 2 = 0.98) with low MSE (107.74) and PRESS (26.96). and R. Kumar, S. Sharma.
The accurate and nondestructive determination of individual leaf area (LA) of plants, by using leaf length (L) and width (W) measurement or combinations of them, is important for many experimental comparisons. Here, we propose reliable and simple regressions for estimating LA across different leaf-age groups of eight common evergreen broadleaved trees in a subtropical forest in Gutianshan Natural Reserve, eastern China. During July 2007, the L, W, and LA of 2,923 leaves (202 to 476 leaves for each species) were measured for model construction and the respective measurements on 1,299 leaves were used for model validation. Mean L, W, LA and leaf shape (L:W ratio) differed significantly between current and older leaves in four out of the eight species. The coefficients of one-dimension LA models were affected by leaf age for most species while those incorporating both leaf dimensions (L and W) were independent of leaf age for all the species. Therefore, the regressions encompassing both L and W (LA = a L W + b), which were independent of leaf age and also allowed reliable LA estimations, were developed. Comparison between observed and predicted LA using these equations in another dataset, conducted for model validation, exhibited a high degree of correlation (R 2 = 0.96-0.99). Accordingly, these models can accurately estimate the LA of different age groups for the eight evergreen tree species without using instruments. and L. Zhang, L. Pan.
We studied the dominant environmental factors that affect the
gas-exchange characteristics and water potential (ψ) of broad-ovate leaves of Populus euphratica Oliv. in extreme arid area of Tarim River, China, and their correlation to water status of P. euphratica by analyzing on-field monitored meteorological data, soil moisture and salinity, P. euphratica leaf gas exchange and ψ, and revealed the indicative threshold of environmental factors for P. euphratica leaf water changes and growth. The results indicated that meteorological factors such as air relative humidity (RH), air temperature (T air), etc. are the dominant factors. The threshold value of RH is (48.19 ± 1.06)% for P. euphratica growth, i.e. RH from 10.69% to 48.19% is suitable for P. euphratica growth in extremely arid region of Tarim River. This study provides a theoretical basis for reducing drought damage to P. euphratica and maintaining normal growth of P. euphratica by in-time watering. and A. H. Fu ... [et al.].
Leaf canopy plays a determining role influencing source-sink relations as any change in source activity (photosynthesis) affects sink metabolism. Defoliation (removal of leaves) influences growth and photosynthetic capacity of plants, remobilizes carbon and nitrogen reserves and accelerates sink metabolism, leading to improved source-sink relations. The response of plants to defoliation could be used to manipulate source-sink relations by removing lower and senescing leaves to obtain greatest photosynthetic capacity and efficient carbon and nitrogen metabolism under optimal and stressful environments. The present work enhances our current understanding on the physiological responses of plants to defoliation and elaborates how defoliation influences growth, photosynthetic capacity and source-sink relations under optimal and changing environmental conditions., N. Iqbal, A. Masood, and N. A. Khan., and Obsahuje bibliografii
At present, research activities on the role of orchard systems in sequestering atmospheric CO2 remain scarce. This paper aimed to contribute to assessing the carbon balance of a Mediterranean olive (Olea europea) orchard. The net ecosystem exchange, the ecosystem respiration and the gross primary production were computed for two consecutive years through eddy covariance, and the different biomass accumulation terms were also inferred in the same period through an inventorial method. The net carbon exchange ranged from 13.45 t(C) ha-1 year-1 to 11.60 t(C) ha-1 year-1. Very similar values [12.2 and 11.5 t(C) ha-1 year-1] were found with the direct carbon accumulation inventory. The intensive farming management (irrigation included) and the young age of the plants (12-16 years old), still in an active growing phase, led the olive plantation to be a higher carbon sink with respect to other evergreen orchards reported in the literature., M. Nardino ... [et al.]., and Obsahuje bibliografii
We studied how the reductions of trienoic fatty acids (TAs) and increases of dienoic fatty acids (DAs) enhanced high-temperature tolerance in antisense expression of tomato chloroplast omega-3 fatty acid desaturase gene (LeFAD7) transgenic tomato (Lycopersicon esculentum Mill.) plants. In transgenic plants, the content of linolenic acid (18:3) was markedly decreased, while linoleic acid (18:2) was increased correspondingly and the similar changes were observed under high-temperature stress as well. Under high-temperature stress, transgenic plants can maintain a relatively higher level of net photosynthetic rate (P N) and chlorophyll (Chl) content than that of wild type (WT) plants. A decreased Chl/Carotenoids (xanthophylls and carotenes, Car) ratio and Chl a/b ratio were observed in transgenic plants. Transgenic plants exhibited visible decrease in the relative electrolyte conductivity, higher activities of antioxidative enzymes and lower reactive oxygen species correspondingly than WT. In addition, high-temperature stress for 24 h caused more extensive changes of chloroplast ultrastructure in WT than in transgenic plants. We therefore suggested that the enhancement of high-temperature tolerance in antisense expression of LeFAD7 transgenic plants might be raised from the reduction of TAs and increase of DAs subsequently leading to series of physiological alterations. and X. Liu ... [et al.].
A tomato (Lycopersicon esculentum Mill.) zeaxanthin epoxidase gene (LeZE) was isolated and antisense transgenic tomato plants were produced. Northern, southern, and western blot analyses demonstrated that antisense LeZE was transferred into the tomato genome and the expression of LeZE was inhibited. The ratio of (A+Z)/(V+A+Z) in antisense transgenic plants was maintained at a higher level than in the wild type (WT) plants under high light and chilling stress with low irradiance. The value of non-photochemical quenching (NPQ) in WT and transgenic plants was not affected during the stresses. The oxidizable P700 and the maximal photochemical efficiency of PSII (Fv/Fm) in transgenic plants decreased more slowly at chilling temperature under low irradiance. These results suggested that suppression of LeZE caused zeaxanthin accumulation, which was helpful in alleviating photoinhibition of PSI and PSII in tomato plants under chilling stress. and N. Wang ... [et al.].
Leaf area estimation is an important measurement for comparing plant growth in field and pot experiments. In this study, determination of the leaf area (LA, cm2) in soybean [Glycine max (L.) Merr] involves measurements of leaf parameters such as maximum terminal leaflet length (L, cm), width (W, cm), product of length and width (LW), green leaf dry matter (GLDM) and the total number of green leaflets per plant (TNLP) as independent variables. A two-year study was carried out during 2009 (three cultivars) and 2010 (four cultivars) under field conditions to build a model for estimation of LA across soybean cultivars. Regression analysis of LA vs. L and W revealed several functions that could be used to estimate the area of individual leaflet (LE), trifoliate (T) and total leaf area (TLA). Results showed that the LW-based models were better (highest R 2 and smallest RMSE) than models based on L or W and models that used GLDM and TNLP as independent variables. The proposed linear models are: LE = 0.754 + 0.655 LW, (R2 = 0.98), T = -4.869 + 1.923 LW, (R2 = 0.97), and TLA = 6.876 + 1.813 ΣLW (summed product of L and W terminal leaflets per plant), (R2 = 0.99). The validation of the models based on LW and developed on cv. DPX showed that the correlation between calculated and measured LA was strong. Therefore, the proposed models can estimate accurately and massively the LA in soybeans without the use of expensive instrumentation. and E. Bakhshandeh, B. Kamkar. J. T. Tsialtas
7-day soil drought followed by 7-day rehydration was applied to potted German chamomile (Chamomilla recutita) plants at the beginning of their generative stage. Plants of a wild type (WT), plus two diploid (2n) and two tetraploid (4n) genotypes were studied, in order to examine the alterations in chlorophyll (Chl) and carotenoids (Car) contents, and chlorophyll fluorescence (CF) parameters during water shortage and rehydration. The fresh mass of the anthodia after the recovery was also studied.
WT plants adjust better to water stress than modern breeding genotypes, because drought resulted in the low fall in leaf water content of WT, the lowest decrease in the fresh mass of its anthodia (a 41% decrease from the control), and the most elastic response of the photosynthetic apparatus. 4n C11/2 strain plants suffered from the highest reduction in anthodia yield (87%), and had the lowest constitutive pigment contents. It was also the only genotype which revealed nontypical alterations in various CF parameters obtained on a dark- and light-adapted leaf. During drought, a big increase was noticed in minimal, maximal, and variable fluorescence of PSII reaction centres in the dark- adapted (F0, Fm and Fv, respectively), and in the light-adapted state (F0', Fm' and Fv')., It was accompanied by the biggest decline in linear electron transport rate (ETR), quantum efficiency of PSII electron transport (ΦPSII) and photochemical quenching coefficient (qP). These alterations were prolonged to the stage when the normal leaf water content was retained. On the contrary, C6/2 strain plants had the highest constitutive Chl and Car contents, which additionally increased after rehydration, similarly to the values of F0, Fm and Fv, which reflects the high photosynthetic potential of this genotype. It was accompanied by the relatively high yield of its anthodia after drought. Considering the drop in the yield triggered by drought, it seems to be the only parameter which may be linked with the ploidy level.
Although the yield formation of chamomile strains cannot simply be estimated by CF assay, this technique may serve as an additional tool in the selection of plants to drought. The following circumstances should be submitted; namely: measurement at the proper developmental stage of plants, in different water regimes, and an analysis of various CF parameters. The increase in F0 and F0', and the reduction in ETR, Fv'/Fm', ΦPSII and qP values in response to water deficit should be an indicator of the impairment of the photosynthetic apparatus through drought., and R. Bączek-Kwinta ... [et al.].
Low temperature has a negative impact on plant cells and results in the generation of reactive oxygen species (ROS). In order to study the role of ascorbate under chilling stress, the response of an ascorbate-deficient Arabidopsis thaliana mutant vtc2-1 to low temperature (2°C) was investigated. After chilling stress, vtc2-1 mutants exhibited oxidative damage. An increase in the H2O2 generation and the production of thiobarbituric acid reactive substances (TBARS), and a decrease in chlorophyll content, the maximal photochemical efficiency of PSII (Fv/Fm) and oxidizable P700 were also noted. The ratio of ascorbate/dehydroascorbate and reduced glutathione/oxidzed glutathione in the vtc2-1 mutants were reduced, compared with the wild type (WT) plants. The activities of antioxidant enzymes, such as catalase (CAT) and ascorbate peroxidase (APX), and soluble antioxidants were lower in the vtc2-1 mutants than those in WT plants. These results suggested that the ascorbate-deficient mutant vtc2-1 was more sensitive to chilling treatment than WT plants. The low temperature-induced oxidative stress was the major cause of the decrease of PSII and PSI function in the vtc2-1 mutants. Ascorbate plays a critical role of defense without which the rest of the ROS defense network is unable to react effectively., L. Y. Wang ... [et al.]., and Obsahuje bibliografii
Previous evidence has demonstrated that vertical leaves of Styrax camporum, a woody shrub from the Brazilian savanna, have a higher net photosynthetic rate (PN) compared with horizontal leaves, and that it is detected only if gas exchange is measured with light interception by both leaf surfaces. In the present study, leaf temperature (T leaf), gas exchange and chlorophyll (Chl) a fluorescence with light interception on adaxial and also on abaxial surfaces of vertical and horizontal mature fully-expanded leaves subjected to water deficit (WD) were measured. Similar
gas-exchange and fluorescence values were found when the leaves were measured with light interception on the respective surfaces of horizontal and vertical leaves. WD reduced N values measured with light interception on leaf surfaces of both leaf types, but the effective quantum yield of PSII (ΦPSII) and the apparent electron transport rate (ETR) were reduced only when the leaves were measured with light interception on the adaxial surface. WD did not decrease the maximum quantum yield of PSII (Fv/Fm) or increase T leaf, even at the peak of WD stress. Vertical leaf orientation in S. camporum is not related to leaf heat avoidance. In addition, the similar P N values and the lack of higher values of ΦPSII and ETR in vertical compared with horizontal leaves measured with light interception by each of the leaf surfaces suggests that the vertical leaf position is not related to photoprotection in this species, even when subjected to drought conditions. The exclusion of this photoprotective role could raise the alternative hypothesis that diverse leaf angles sustain whole plant light interception efficiency increased in this species., A. M. Feistler, G. Habermann., and Obsahuje bibliografii
This study compared physiological and growth responses to water stress of two legume species during the seedling stage. Potted alfalfa (Medicago sativa L. cv. Algonquin) and milkvetch (Astragalus adsurgens Pall. cv. Pengyang earlymaturing vetch) seedlings were grown under well-watered [soil water content (SWC) maintained at 14.92% daily] or water-stressed conditions (drying) for 15 days. Net photosynthetic rate (PN), transpiration rate (E) and stomatal conductance (gs) of both species decreased parabolically. When SWC decreased to 7.2% and 10.3%, gs values for alfalfa and milkvetch were significantly different from those of the respective well-watered plants (p<0.05). When SWC decreased to 6.6% for alfalfa and 6.8% for milkvetch, leaf water potentials (ψL) were significantly different from those of the well-watered plants (p<0.05). Thus the difference between the SWC thresholds for a nonhydraulic root signal (nHRS) and a hydraulic root signal (HRS) were 0.6% and 3.5% for alfalfa and milkvetch, respectively. Milkvetch had a lower gs than alfalfa for a given SWC (p<0.05). Although alfalfa seedlings had a higher dry mass (DM) and root:shoot ratio (R/S) than milkvetch in both treatments (p<0.05), we concluded that milkvetch seedlings had greater drought tolerance than alfalfa. and B.-C. Xu ... [et al.].
In the past decades, it has become clear that superoxide radical (O2 .-) can be generated from photosystem II (PSII) during photosynthesis. Depending on the extent of its accumulation, O2 .- plays an important role in plant physiology and pathology. The photoinhibition/repair cycle is a typical process in PSII which is mainly responsible for the survival of plants under the photoinihibition condition. It is therefore of significant importance to determine O2 .- production in this cycle, and then explore how O2 .- is controlled by PSII within a normal physiological level. With this in mind, we herein investigate the variation of the O2 .- levels in PSII under Mn-depleted and photoactivated conditions mimicking the photoinhibition/repair cycle in vitro. The effect of intrinsic SOD-like component on the O2 .- levels was also studied. Results show that PSII has the ability to regulate the O2 .- levels in these two processes by simultaneously modulating the O2 .- generation activity and intrinsic SOD-like activity. This finding could shed new lights on the photoprotective property of PSII against O2 .- and other reactive oxygen species. and Y. G. Song ... [et al.].
Tomato and pepper leaves were clipped with black leaf clips for dark adaptation under solar radiation in the late spring or early summer 2010 in southern Italy. The leaves showed highly variable maximum PSII quantum yield (Fv/Fm = 0.026-0.802) using a continuous-excitation fluorometer Pocket PEA. These results were confirmed using the modulated fluorometer FMS1 on tomato leaves in mid summer, with Fv/Fm as low as 0.222 ± 0.277 due to nearly equal minimum (F0) and maximum (Fm) fluorescence emission. A significant clip effect on Fv/Fm occurred after only 12 (tomato) or 25 (pepper) min. Increasing the leaf temperature from 25 to 50°C reportedly induced an F0 increase and Fm decrease so that Fv/Fm approached zero. The hypothesis that black leaf clips overheated under intense solar irradiance was verified by shrouding the clipped leaves with aluminum foil. In clipped leaves of pepper, Fv/Fm with the black clip/Pocket-PEA was 0.769 ± 0.025 (shrouded) and as low as 0.271 ± 0.163 (nonshrouded), the latter showing a double F0 and 32% lower Fm. An 8% clip effect on Fv/Fm was observed with the white clip/FMS1. To avoid the clip effect in high irradiance environments, Fv/Fm measurements with black clip/Pocket PEA system required leaf dark adaptation with
radiation-reflecting shrouds. It would be useful if manufacturing companies could develop better radiation-reflecting leaf clips for the Pocket PEA fluorometer. and P. Giorio.
The use of black leaf-clips for dark adaptation under high solar radiation conditions is reported to underestimate the maximum quantum yield of PSII photochemistry (Fv/Fm) measured by the continuous-excitation fluorometer Pocket PEA. The decrease in Fv/Fm was due to a rise in minimum fluorescence emission (F0), probably resulting from increased leaf temperature (Tl). In
field-grown tomato and pepper, fluorescence parameters and Tl in the region covered by the black leaf clip were measured in clipped leaves exposed to solar radiation during dark adaptation (clipped-only leaves) and in clipped leaves protected from solar radiation by aluminium foil (shrouded clipped leaves). Results confirmed significant Fv/Fm underestimates in clipped-only leaves primarily due to increased F0. In one tomato experiment, Tl increased from 30 to 44.5°C in clipped-only leaves, with a negligible rise in shrouded clipped leaves. In two respective pepper experiments, Tl in clipped-only leaves increased from 27 to 36.2°C and 33 to 40.9°C. Based on the results of this study, a clip-effect parameter (PCE) on fluorescence emission is proposed as the difference for Fv/Fm (or -F0/Fm) between shrouded clipped leaves and clipped-only leaves, which resulted to be 0.706 for tomato, and 0.241 and 0.358 for the two pepper experiments., P. Giorio ... [et al.]., and Obsahuje bibliografii
Seedling performance may determine plant distribution, especially in water-limited environments. Plants of Caragana korshinskii commonly grow in arid and semiarid areas in northwestern China, and endure water shortage in various ways, but little is known about their performance when water shortage occurs at early growth stages. The water relations, photosynthetic activity, chlorophyll (Chl) content and proline accumulation were determined in 1-year-old seedlings growing in a 1:1 mixture of Loess soil and Perlite and subjected to (1) a water deficit for 20 days and (2) kept adequately watered throughout. The water deficit induced low (-6.1 MPa) predawn leaf water potentials (LWP), but did not induce any leaf abscission. Stomatal conductance (gs), leaf transpiration rate (E), and net photosynthetic rate (PN) decreased immediately following the imposition of the water deficit, while the maximal photochemical efficiency of photosystem II (PSII) (Fv/Fm) and the effective quantum yield of PSII (ΦPSII) decreased 15 days later. An early and rapid decrease in gs, reduced E, increased Chl (a+b) loss, increased the apparent rate of photochemical transport of electrons through PSII (ETR)/PN, as well as a gradual increase in non-photochemical quenching of fluorescence (NPQ) and proline may have contributed to preventing ΦPSII from photodamage. C. korshinskii seedlings used a stress-tolerance strategy, with leaf maintenance providing a clear selective advantage, considering the occasional rainfall events during the growing season. and X. W. Fang ... [et al.].
The size, shape, and number of chloroplasts in the palisade and spongy parenchyma layers of Haberlea rhodopensis leaves changed significantly during desiccation and following rehydration. The chloroplasts became smaller and more rounded during desiccation, and aggregated in the middle of the cell. The size and number of chloroplasts in the palisade parenchyma cells were higher than in spongy parenchyma. The good correlation observed between the size or number of chloroplasts and the cross-sectional area of mesophyll cells, the cross-sectional width of the leaf and its water content suggested that the palisade cells were more responsive to water availability than the spongy cells. Changes in chloroplast number during desiccation and rehydration process are characteristic features for desiccation-tolerant plants (especially in homoiochlorophyllous strategy). and H. Nagy-Déri ... [et al.].
Photosynthesis, chlorophyll (Chl) a fluorescence, and nitrogen metabolism of hawthorn (Crataegus pinnatifida Bge.), subjected to exogenous L-glutamic acid (GLA) (200 mg l-1, 400 mg l-1, and 800 mg l-1) that possibly affect secondary metabolic regulation, were measured. The results indicated that photosynthetic and fluorescence characteristics of hawthorn exhibited positive responses to the application of GLA. Different concentrations of GLA caused an increase in Chl content, net photosynthetic rate
(PN) and stomatal conductance (g s) as well as transpiration rate (E), and improved the carboxylation efficiency (CE), apparent quantum yield (AQY) and maximum carboxylation velocity of Rubisco (Vcmax). Application of GLA could also enhance the maximum ratio of quantum yields of photochemical and concurrent non-photochemical processes in PSII (Fv/F0), the maximal quantum yield of PSII (Fv/Fm), the probability that an absorbed photon will move an electron into the electron transport chain beyond QA (ΦEo) as well as the performance index on absorption basis (PIABS), but decreased the intercellular CO2 concentration
(Ci) and the minimal fluorescence (F0). Application of GLA also induced an increase in nitrate reductase (NR; EC 1.6.6.1) and glutamine synthetase (GS; EC 6.3.1.2) activities, and increased the soluble protein content, leaf nitrogen (N) content and N accumulation in leaves as well as the plant biomass. However, the effects were different among different concentrations of GLA, and 800 mg l-1 GLA was better. This finding suggested that application of GLA is recommended to improve the photosynthetic capacity by increasing the light energy conversion and CO2 transfer as well as the photochemical efficiency of PSII, and enhanced the nitrogen metabolism and growth and development of plants. and C. YU ... [et al.].
The leaf water potential, gas-exchange parameters and chlorophyll fluorescence were evaluated in five common oil palm (Elaeis guineensis Jacq.) tenera hybrids 913X1988, 1425X2277, 748X1988, 7418X1988, and 690X1988 under water deficit with an aim to identify hybrids which can cope up better under such conditions and understand possible differences among hybrids in relation to the physiological mechanisms triggered by water deficit. Our findings indicate oil palm hybrids 913X1988, 1425X2277, and 7418X1988 maintained higher leaf water potentials than the other hybrids. Hybrids 7418X1988 and 1425X2277 recorded lower stomatal conductance after water deficit, which resulted in higher intrinsic water-use efficiency. The excess light energy produced due to decreased photosynthesis in 7418X1988 and 690X1988 hybrids under water deficit was dissipated as heat by higher nonphotochemical quenching. The maximum efficiency of photosystem II was not affected, even after withholding water for 24 days, suggesting an increased efficiency of photoprotection mechanisms in all these oil palm hybrids., K. Suresh ... [et al.]., and Obsahuje bibliografii
Measurements of Sorbus stomata size and density, maximal photochemical efficiency of photosystem II (Fv/Fm),
variable-to-initial fluorescence ratio (Fv/F0) and potential electron acceptor capacity (‘area’) were performed during leaf development in four parental diploid species, S. aria, S. aucuparia, S. chamaemespilus, S. torminalis, and two hybrid species, S. hazslinszkyana and S. intermedia. In fully expanded mature leaves, stomata lengths and densities were significantly larger in the shrub S. chamaemespilus than in the five tree species. The best performance of both the Fv/Fm and the Fv/F0 ratio was recorded in S. intermedia, whereas S. chamaemespilus had the highest value of ‘area’. From a physiological point of view, the results of this study showed that the photosystem II reaction centers remained intact functionally through all phenological stages of leaf expansion for all examined species of Sorbus., I. Čaňová ... [et al.]., and Obsahuje bibliografii
By using a wild-type rice (Oryza sativa L. cv. Norin No. 8) and the chlorophyll (Chl) b-deficient mutant derived from Norin No. 8 (chlorina 11), the present study monitored the oxygen evolution, contents of Chl a and b, β-carotene, and lutein in leaf and the contents of cytochrome f, and the reaction centres of photosystem I (PSI) and photosystem II (PSII) in thylakoids. The oxygen evolution, maximal quantum yield of PSII (Fv/Fm) and Chl concentration remained constant in both Norin No. 8 and chlorina 11 under 5 and 2% of full sunlight for six days. On the other hand, on the thylakoid level, the PSII reaction centre of chlorina 11 was more stable even under high irradiance, while approximately 40% decrease in levels of the PSII reaction centre occurred under 2% of full sunlight for six days. However, under such conditions, by regulating the stoichiometry of active PSII and PSI centres, the light absorption balance in both rice types was adjusted between the two photosystems. The present study attempted to examine whether the light absorption balance between PSII and PSI is altered to effectively conduct photosynthesis in the wild-type and Chl b-deficient mutant rice seedlings. and J. Yamazaki.
Differences in structural, physiological, and biochemical features between C3 and C4 species resulted in different wateruse efficiencies and different adaptations to climate. This paper aimed at investigating, at a late successional stage, the water-use efficiency of two forage species, Dichanthium ischaemum and Dasypyrum villosum, which exhibit different growth forms (perenial, annual) and photosynthetic mechanisms (C4 and C3, respectively). The annual C3 species Avena fatua, at an early successional stage, was included in our experiments to contrast its behaviour against D. villosum. The experiment was conducted during the growing season in low-elevation grasslands of North Greece. Midday leaf water potential, net photosynthetic rate, transpiration rate and stomatal conductance were measured. Instantaneous water-use efficiency (WUE) and intrinsic water-use efficiency (WUEi) were calculated in D. ischaemum, D. villosum, and A. fatua. The results suggest that, under natural rainfall conditions, the annual C3 grass species D. villosum exhibits a similar WUE with higher values of WUEi than the perennial C4 species
D. ischaemum at late stage of succession on the low elevation Mediterranean grasslands. Moreover, A. fatua at an early successional stage, exhibited different photosynthetic behaviour than D. villosum at a late successional stage. These findings indicate that the annual C3 species D. villosum under drought and at a late successional stage seems to modify the WUE obtaining values similar to those of C4 species. The extent to which the ecophysiological characteristics of D. villosum are environmentally or intrinsically determined remains to be answered. and M. Karatassiou, B. Noitsakis.
Primulina tabacum Hance is an endangered perennial herb distributed in calcium-rich and nitrogen-limited soil of the karst limestone areas in southern China. The morphological, ultrastructural, and physiological traits were determined for P. tabacum populations growing in three different environment conditions: twilight zone of a cave (site TZ, extremely low light intensity), at a cave entrance (site EZ, low light intensity), and in an open area (site OA, high light intensity). At site OA, P. tabacum plants were exposed to high light (635 μmol m-2 s-1 of mean daily photosynthetically active radiation) with drought stress, and expressed traits to minimize light capture and water loss. Compared to plants at sites EZ and TZ, those at site OA had thicker leaves with higher densities of stomata and pubescence, higher palisade/spongy ratio, higher light-saturated rate of net photosynthetic rate (Pmax), higher biomass, higher non-photochemical quenching coefficient (NPQ), and higher light saturation point (LSP) but fewer grana per chloroplast and less thylakoid stacking per granum. In contrast, P. tabacum growing at the cave vicinities: EZ (mean daily irradiance 59 μmol m-2 s-1) and TZ (mean daily irradiance 11 μmol m-2 s-1) showed typical shade-adapted characteristics for optimum light capture. The presence of sun- and shade-adapted characteristics indicates that P. tabacum has different strategies to cope with different environments but whether these strategies reflect genetic selection or phenological plasticity is yet to be determined. Such variability in physiological and morphological traits is important for the survival of P. tabacum in heterogeneous light conditions. and K. M. Liang ... [et al.].
The major light-harvesting chlorophyll (Chl) a/b complexes of photosystem II (LHCIIb) play important roles in energy balance of thylakoid membrane. They harvest solar energy, transfer the energy to the reaction center under normal light condition and dissipate excess excitation energy under strong light condition. Many bamboo species could grow very fast even under extremely changing light conditions. In order to explain whether LHCIIb in bamboo contributes to this specific characteristic, the spectroscopic features, the capacity of forming homotrimers and structural stabilities of different isoforms (Lhcb1-3) were investigated. The apoproteins of the three isoforms of LHCIIb in bamboo are overexpressed in vitro and successfully refolded with thylakoid pigments. The sequences of Lhcb1 and Lhcb2 are similar and they are capable of forming homotrimer, while Lhcb3 lacks 10 residues in the N terminus and can not form the homotrimeric structure. The pigment stoichiometries, spectroscopic characteristics, thermo- and photostabilities of different reconstituted Lhcbs reveal that Lhcb3 differs strongly from Lhcb1 and Lhcb2. Lhcb3 possesses the lowest Qy transition energy and the highest thermostability. Lhcb2 is the most stable monomer under strong illumination among all the isoforms. These results suggest that in spite of small differences, different Lhcb isoforms in bamboo possess similar characteristics as those in other higher plants., Z. H. Jiang ... [et al.]., and Obsahuje bibliografii
To investigate whether brassinosteroids (BRs) could be used to alleviate chill-induced inhibition of photosynthesis in cucumber (Cucumis sativus L) during chilling and subsequent recovery, the effects of exogenously applied 24-epibrassinolide (EBR) on gas exchange, chlorophyll fluorescence parameters, and antioxidant enzyme activity were studied. Cucumber plants were exposed to chilling under low light (12/8°C and 100 μmol m-2 s-1 PPFD) for 3 days and then recovered under normal temperature and high irradiance (28/18°C and 600 μmol m-2 s-1 PPFD) for 6 days. Chilling significantly decreased the net photosynthetic rate (PN) and stomatal conductance (g s), and increased rate of O2 .- formation and H2O2 and malondialdehyde (MDA) content in cucumber leaves, but did not influence the optimal quantum yield of PSII (Fv/Fm). Chilling also decreased the effective quantum yield of PSII photochemistry (ΦPSII) and photochemical quenching (qP), but induced an increase in nonphotochemical quenching (NPQ), and the activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX). High irradiance (600 μmol m-2 s-1) further aggravated the decrease in PN, gs, ΦPSII and qP, and enhanced the increase in reactive oxygen species (ROS) generation and accumulation in the first day of recovery after chilling. However, high irradiance induced a sharp decrease in Fv/Fm and NPQ, as well as the activities of SOD and APX on the first day of recovery. EBR pretreatment significantly alleviated chill-induced inhibition of photosynthesis during chilling stress and subsequent recovery period, which was mainly due to significant increases in gs, ΦPSII, qP and NPQ. EBR pretreatment also reduced ROS generation and accumulation, and increased the activities of SOD and APX during chilling and subsequent recovery. Those results suggest that EBR pretreatment alleviates the chill reduction in photosynthesis and accelerated the recovery rate mainly by increasing of the stomatal conductance, the efficiency of utilization and dissipation of leaf absorbed light, and the activity of the ROS scavenging system during chilling and subsequent recovery period. and W. H. Hu ... [et al.].
The effect of Potato virus Y NTN (PVY) infection upon photosynthesis was analysed in transgenic Pssu-ipt tobacco overproducing endogenous cytokinins in comparison with control, nontransgenic Nicotiana tabacum plants. The course of the infection from the early to the late stage was monitored by measuring of photosynthetic gas exchange and fast chlorophyll (Chl) a fluorescence induction kinetics. Leaf photosynthesis was also analysed using Chl fluorescence imaging (Chl-FI). From the different fluorescence parameters obtained using Chl-FI, the nonphotochemical quenching (NPQ) proved to be the most useful parameter to assess the effect of PVY infection. On the other hand, Chl-FI was found to be inapplicable for any presymptomatic detection of PVY infection in tobacco. The lower accumulation of the virus was found in transgenic plants and corresponded also with the presence of visible symptoms of PVY infection. The net photosynthetic rate (PN), transpiration rate (E), and stomatal conductance (gs) significantly decreased with the progress of the infection in both control plant types and transgenic rooted plants, while transgenic grafts were much less affected. The analysis of the Chl fluorescence transient revealed higher number of silent dissipative reaction centres, higher nonphotochemical dissipation, and significantly lower performance index, PI(abs), in the healthy transgenic grafts. Chl-FI also confirmed significantly higher NPQ in transgenic grafts., P. Spoustová ... [et al.]., and Obsahuje bibliografii
In order to assess the long-term impacts of saline groundwater irrigation to Haloxylon ammodendron, one of the main shrubs in the Tarim desert highway ecological shelterbelt, we irrigated the H. ammodendron seedlings with progressive saline groundwater (3-30 g L-1, simulation environment in the Tarim desert highway ecological shelterbelt) and investigated the diurnal variations of chlorophyll a (Chl a) fluorescence parameters, such as maximal quantum yield of photosystem II (PSII) photochemistry (Fv/Fm), quantum yield of photochemical energy conversion in PSII (YII), the apparent rate of electron transport at the PSII level (ETR), photochemical quenching coefficient (qP), non-photochemical quenching (NPQ), quantum yield of nonregulated non-photochemical energy loss in PSII (YNO) and quantum yield of regulated non-photochemical energy loss in PSII (YII), at approximately 2-h intervals. Fv/Fm with 5 g L-1 (S2) was lower than that with 2 g L-1 (S1) but a little higher than 20 g L-1 (S5), respectively. Under the low light [photosyntheticallyactive radiation (PAR) ≤ 250 μmol m-2 s-1, at 08:00, 10:00 and 20:00 h of the local time], S1 kept the lowest YII and the highest YNPQ; while under the high light (PAR ≥ 1500 μmol m-2 s-1), the YII performed S1>S2>S5, and the reverse YNPQ; under mild light (250 μmol mt-2 s-1 ≤ PAR ≤ 1500 μmol m-2 s-1), S1 remained the highest YII, no matter the light and the salinity, the similar YNO almost occurred basically. The results showed that the sand-binding plant H. ammodendron could regulate its energy-utilizing strategies. The S2 might be the most suitable salinity of the irrigation water for H. ammodendron in the Tarim desert highway ecological shelterbelt in the northwest of China. and W. Han ... [et al.].
Chlorophyll (Chl) a fluorescence parameters and rapid light curves of soybean [Glycine max (L.) Merrill] were measured by pulse amplitude modulation fluorometry. Measurements were taken during different stages of soybean growth under field conditions with 20% enhancement in ultraviolet-B (UV-B) radiation. Results showed that supplemental UV-B radiation decreased Chl contents by 5.5% (P=0.048), 8.7% (P=0.046), and 10.5% (P=0.005) in seedling, in branching-flowering, and in pod-setting stages, respectively. In the branching-flowering and pod-setting stages, maximum quantum yield of photosystem (PS) II photochemistry (Fv/Fm) decreased by 6.1% (P=0.001) and 3.0% (P=0.009), respectively. Supplemental UV-B radiation significantly decreased the effective quantum yield (Y). The photosynthetic capacity at light saturation (Pm) also decreased in both the seedling and branching-flowering stages by 28.9% (P=0.007) and 15.5% (P=0.041), respectively. However, Y and Pm showed no significant difference in the trefoil and pod-setting stages with and without the UV treatment. The light saturation parameter (E k) decreased by 21.1% (P=0.000) and 23.2% (P=0.029) in the trefoil and seedling stages, respectively. Moreover, the initial slope (α) decreased by 21.1% (P=0.001) in the branching-flowering stage. Nonphotochemical quenching (NPQ) in the seedling stage and photochemical quenching coefficient (qp) in the
branching-flowering stage decreased significantly under UV-B treatments. The results of the present study suggest that supplemental UV-B radiation adversely affected Chl content and electron transport activity in PSII and consequently decreased the photosynthetic efficiency of soybean plants., Z. Hu ... [et al.]., and Obsahuje bibliografii
This study examined the utility of the ratio of variable fluorescence to maximum fluorescence (Fv/Fm) to detect freezing injury on buds of two Vitis vinifera cultivars: Pinot noir and Pinot gris. Freezing treatments on buds caused a decrease both in Fv/Fm and percentage of budburst, more severely on Pinot gris than Pinot noir, specifically at the lower temperature (-20°C). Fv/Fm ratio showed a close correlation with percentage of budburst, and a threshold of the lethal Fv/Fm was proposed as an indicator of bud mortality. and L. Zulini, C. Fischer, M. Bertamini.
a1_Photosynthesis is one of the most important processes in plant biology and in the development of new methodologies that allow a better understanding and characterization of the photosynthetic status of organisms, which is invaluable. Flow cytometry (FCM) is an excellent tool for measuring fluorescence and physical proprieties of particles but it has seldom been used in photosynthetic studies and thus the full extent of its potentialities, in this field of research, remains unknown. To determine the suitability of FCM in photosynthesis studies, pea plants were exposed to Paraquat and their status was analyzed during 24 h. FCM was used to evaluate the integrity (volume and internal complexity) and the relative fluorescence intensity (FL) of chloroplasts extracted from those plants. To elucidate which type of information the FL conveys, FL values were correlated with the minimum fluorescence level (F0), maximum fluorescence level (Fm) and maximum photochemical efficiency of PSII (Fv/Fm), obtained by using Pulse-Amplitude-Modulation (PAM) fluorometry. Results indicate that: (1) the biomarkers used to evaluate the structural integrity of the chloroplasts were more sensitive to Paraquat exposure than the ones related to fluorescence; (2) the variation of the chloroplast’s structure, as time progressed, pointed to a swelling and subsequent burst of the chloroplast which, in turn, compromised fluorescence emission; (3) FL presented a high and significant correlation with the Fv/Fm and to a lesser degree with Fm but not with F0; (4) pigment content did not reveal significant changes in response to Paraquat exposure and is in agreement with the proposed model, suggesting that the cause for fluorescence decrease is due to chloroplast disruption., a2_In sum, FCM proved to be an outstanding technique to evaluate chloroplastidal functional and structural status and therefore it should be regarded as a valuable asset in the field of photosynthetic research., E. Rodriguez ... [et al.]., and Obsahuje bibliografii
Changes in chloroplastidic pigments, gas exchange and carbohydrate concentrations were assessed during the rapid initial expansion of C. guianensis leaflet. Leaves at metaphyll stage were tagged and assessments were carried out 14, 17, 20, 23, 27, and 31 days later. Pigments synthesis, distribution and accumulation were uniform among leaflet sections (basal, median and apical). Chlorophyll (Chl) a, Chl b, Chl (a+b), and total carotenoids (Car) concentrations were significantly increased after 27 days from metaphyll, and the most expressive increases were parallel to lower specific leaflet area. Chl a/b was lower on day 14 and it was increased on subsequent days. Negative net photosynthesis rate (PN), and the lowest stomatal conductance (gs) and transpiration (E) were registered on day 14, following significant increases on subsequent days. The Chl (a+b) and Chl a effects on PN were more expressive until day 20. Intercellular to ambient CO2 concentration ratio (Ci/Ca) was higher on day 14 and lower on subsequent days, and no stomatal limitation to CO2 influx inside leaflets was observed. Leaflet temperature was almost constant (ca. 35°C) during leaflet development. Sucrose and starch concentrations were increased in parallel to increases in PN. Altogether, these results highlight the main physiological changes during C. guianensis leaflet expansion and they should be considered in future experiments focusing on factors affecting PN in this species. and F. K. C. Moraes ... [et al.].
Most organisms inhabiting earth feed directly or indirectly on the products synthesized by the reaction of photosynthesis, which at the current atmospheric CO2 levels operates only at two thirds of its peak efficiency. Restricting the photorespiratory loss of carbon and thereby improving the efficiency of photosynthesis is seen by many as a good option to enhance productivity of food crops. Research during last half a century has shown that several plant species developed CO2-concentrating mechanism (CCM) to restrict photorespiration under lower concentration of available CO2. CCMs are now known to be operative in several terrestrial and aquatic plants, ranging from most advanced higher plants to algae, cyanobacteria and diatoms. Plants with C4 pathway of photosynthesis (where four-carbon compound is the first product of photosynthesis) or crassulacean acid metabolism (CAM) may consistently operate CCM. Some plants however can undergo a shift in photosynthetic metabolism only with change in environmental variables. More recently, a shift in plant photosynthetic metabolism is reported at high altitude where improved efficiency of CO2 uptake is related to the recapture of photorespiratory loss of carbon. Of the divergent CO2 assimilation strategies operative in different oraganisms, the capacity to recapture photorespiratory CO2 could be an important approach to develop plants with efficient photosynthetic capacity. and S. K. Vats, S. Kumar, P. S. Ahuja
Geitlerinema amphibium (BA-13), mat-forming cyanobacterium from the southern Baltic Sea, was grown at three irradiances [5, 65, and 125 μmol(photon) m-2 s-1] and three temperatures (15, 22.5, and 30°C). To determine the effect of the investigated factors and their interaction on culture concentration, pigment content, and photosynthetic parameters of cyanobacterium, factorial experiments and two-way analysis of variance (ANOVA) were carried out. Both chlorophyll (Chl) a and phycobilins (PB) were influenced by the irradiance and temperature, but stronger effect was noted in the case of the former one. Chl a and PB concentration per 100 μm of filament dropped above 4-fold with the increasing irradiance. The ratios between individual carotenoids [β-carotene, zeaxanthin, and myxoxanthophyll (Myx)] and Chl a increased significantly with an increase in the irradiance. The greatest fluctuations were observed in the ratio of Myx to Chl a (above 10-fold). Thus, Myx was suggested as the main photoprotective carotenoid in G. amphibium. Based on photosynthetic light response (PI) curves, two mechanisms of photoacclimation in G. amphibium were recognized: a change of photosynthetic units (PSU) number and a change of PSU size. These two mechanisms constituted the base of significant changes in photosynthetic rate and its parameters, such as the compensation point (PC), the initial slope of photosynthetic curve (α), saturation irradiance (EK), maximal photosynthetic rate (Pmax), and dark respiration rate (RD). The greatest changes were observed in PC values (about 15-fold within the range of the factors tested). Studied parameters showed a wide range of changes, which might indicate G. amphibium ability to acclimatize well to irradiance and temperature, and indirectly might explain the successful growth of cyanobacterium in dynamically changing environmental conditions., S. Jodłowska, A. Latała., and Obsahuje bibliografii
The present piece of work highlights the comparative effects of two active forms of brassinosteroids (BRs), 28-homobrassinolide (HBL) and 24-epibrassinolide (EBL), on growth parameters, carbonic anhydrase activity and photosynthetic parameters in Lycopersicon esculentum (cv. K-21) sampled at 45 (24 h after spray) and 60 days after sowing, under natural conditions. Out of the two active forms of BR, EBL proved better than HBL in improving the above parameters, when applied as foliar spray. Of the three concentrations (10-6 M, 10-8 M or 10-10 M) of HBL and EBL, 10-8M proved best in both cases. and S. Hayat ... [et al.].
In this study, cotton seedlings were subjected to osmotic-, salt- and alkali stresses. The growth, photosynthesis, inorganic ions, and organic acids in the stressed seedlings were measured, to compare the mechanisms by which plants adapt to these stresses and attempt to probe the mechanisms by which plants adapt to high pH stress. Our results indicated that, at high stress intensity, both osmotic and alkali stresses showed a stronger injurious effect on growth and photosynthesis than salt stress. Cotton accumulated large amount of Na+ under salt and alkali stresses, but not under osmotic stress. In addition, the reductions of K+, NO3 -, and H2PO4 - under osmotic stress were much greater than those under salt stress with increasing stress intensity. The lack of inorganic ions limited water uptake and was the main reason for the higher injury from osmotic-compared to salt stress on cotton. Compared with salt- and alkali stresses, the most dramatic response to osmotic stress was the accumulation of soluble sugars as the main organic osmolytes. In addition, we found that organic acid metabolism adjustment may play different roles under different types of stress. Under alkali stress, organic acids might play an important role in maintaining ion balance of cotton; however, under osmotic stress, malate might play an important osmotic role. and W. Chen ... [et al.].
Field trials under rain-fed conditions at the International Center for Tropical Agriculture (CIAT) in Colombia were conducted to study the comparative leaf photosynthesis, growth, yield, and nutrient use efficiency in two groups of cassava cultivars representing tall (large leaf canopy and shoot biomass) and short (small leaf canopy and shoot biomass) plant types. Using the standard plant density (10,000 plants ha-1), tall cultivars produced higher shoot biomass, larger seasonal leaf area indices (LAIs) and greater final storage root yields than the short cultivars. At six months after planting, yields were similar in both plant types with the short ones tending to form and fill storage roots at a much earlier time in their growth stage. Root yield, shoot and total biomass in all cultivars were significantly correlated with seasonal average LAI. Short cultivars maintained lower than optimal LAI for yield. Seasonal PN, across cultivars, was 12% greater in short types, with maximum values obtained in Brazilian genotypes. This difference in PN was attributed to nonstomatal factors (i.e., anatomical/biochemical mesophyll characteristics). Compared with tall cultivars, short ones had 14 to 24 % greater nutrient use efficiency (NUE) in terms of storage root production. The lesser NUE in tall plants was attributed mainly to more total nutrient uptake than in short cultivars. It was concluded that short-stemmed cultivars are superior in producing dry matter in their storage roots per unit nutrient absorbed, making them advantageous for soil fertility conservation while their yields approach those in tall types. It was recommended that breeding programs should focus on selection for more efficient short- to medium-stemmed genotypes since resource-limited cassava farmers rarely apply agrochemicals nor recycle residual parts of the crop back to the soil. Such improved short types were expected to surpass tall types in yields when grown at higher than standard plant population densities (>10,000 plants ha-1) in order to maximize irradiance interception. Below a certain population density (<10,000 plants ha-1), tall cultivars should be planted. Findings were discussed in relation to cultivation and cropping systems strategies for water and nutrient conservation and use efficiencies under stressful environments as well as under predicted water deficits in the tropics caused by trends in global climate change. Cassava is expected to play a major role in food and biofuel production due to its high photosynthetic capacity and its ability to conserve water as compared to major cereal grain crops. The interdisciplinary/interinstitutions research reported here, including, an associated release of a drought-tolerant, short-stem cultivar that was eagerly accepted by cassava farmers, reflects well on the productivity of the CIAT international research in Cali, Colombia., and M. A. El-Sharkawy, S. M. de Tafur
The effects of potassium (K) deficiency on chlorophyll (Chl) content, photosynthetic gas exchange, and photosystem II (PSII) photochemistry during the seedling stage were investigated in two soybean [Glycine max (L.) Merr.] cultivars, low-K sensitive Tiefeng31 and low-K tolerant Shennong6. The cultivars were grown hydroponically in K-sufficient (KS) and K-deficient (KD) solutions. Photosynthetic gas exchange and Chl content in Tiefeng31 were severely affected by the low K condition, but were almost unaffected in Shennong6. This difference is in accordance with the PSII photochemistry in the plants, indicating that the photosynthetic apparatus of Shennong6 is more tolerant to low-K stress than that of Tiefeng31. and X.-T. Li ... [et al.].
The parameters estimated from traditional A/Ci curve analysis are dependent upon some underlying assumptions that substomatal CO2 concentration (Ci) equals the chloroplast CO2 concentration (Cc) and the Ci value at which the A/Ci curve switches between Rubisco- and electron transport-limited portions of the curve (Ci-t) is set to a constant. However, the assumptions reduced the accuracy of parameter estimation significantly without taking the influence of Ci-t value and mesophyll conductance (gm) on parameters into account. Based on the analysis of Larix gmelinii's A/Ci curves, it showed the Ci-t value varied significantly, ranging from 24 Pa to 72 Pa and averaging 38 Pa. t-test demonstrated there were significant differences in parameters respectively estimated from A/Ci and A/Cc curve analysis (p<0.01). Compared with the maximum ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation rate (Vcmax), the maximum electron transport rate (Jmax) and Jmax/Vcmax estimated from A/Cc curve analysis which considers the effects of gm limit and simultaneously fits parameters with the whole A/Cc curve, mean Vcmax estimated from A/Ci curve analysis (Vcmax-Ci) was underestimated by 37.49%; mean Jmax estimated from A/Ci curve analysis (Jmax-Ci) was overestimated by 17.8% and (Jmax-Ci)/(Vcmax-Ci) was overestimated by 24.2%. However, there was a significant linear relationship between Vcmax estimated from A/Ci curve analysis and Vcmax estimated from A/Cc curve analysis, so was it Jmax (p<0.05). and W. Zeng ... [et al.].
a1_Photosynthetic gas exchange, dry mass production, water relations and inducibility of crassulacean acid metabolism (CAM) pathway as well as antioxidative protection during the C3-CAM shift were investigated in Sedum album and Sedum stoloniferum from Crassulaceae under water stress for 20 days. Leaf relative water content (RWC), leaf osmotic and water potential decreased with increasing water stress in both studied species. Significant reduction in dry matter production and leaf thickness was detected only in S. stoloniferum after 20-d water stress. Δtitratable acidity and phosphoenolpyruvate carboxylase (PEPC) activity in S. album responded to drought at early stages of stress treatment, continued to increase throughout the entire stress period and reached levels 15 times higher than those in well-watered plants. In S. stoloniferum, however, both parameters responded later and after a transient increase declined again. In S. stoloniferum, in spite of increase by drought stress, net night-time CO2 assimilation was negative resembling a C3-like pattern of gas exchange. Catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) activities increased in plants subjected to mild water stress while declined as the stress became severe. Although malondialdehyde (MDA) content was higher in drought-stressed S. stoloniferum, the increase in the concentration of hydrogen peroxide (H2O2) that may act as a signal for C3-CAM transition was higher in S. album compared with S. stoloniferum. In drought-stressed plants, SOD activity showed a clear diurnal fluctuation that was more steadily expressed in S. album. In addition, such pattern was observed for CAT only in S. album. We concluded that temporal and diurnal fluctuation patterns in the activity of antioxidant enzymes depended on duration of drought stress and was related to the mode of photosynthesis and degree of CAM induction., a2_According to our results, S. stoloniferum developed a low degree of CAM activity, e.g. CAM-cycling metabolism, under drought conditions., G. Habibi, R. Hajiboland., and Obsahuje bibliografii
The diurnal trends of gas exchange and chlorophyll fluorescence parameters in four Lycoris species (L. houdyshelii, L. aurea, L. radiata var. pumila and L. albiflora) were determined and compared with a portable photosynthesis analysis system. Our study revealed that L. houdyshelii had the lowest light compensation point (LCP), while the other three species had higher LCP (12.37-14.99 μmol m-2 s-1); L. aurea had the highest light saturation point (LSP) (1,189 μmol m-2 s-1), and L. houdyshelii and L. albiflora had lower LSP with the values being 322 and 345 μmol m-2 s-1, respectively, and L. radiata var. pumila showed the intermediate LSP. Both the species L. houdyshelii and L. albiflora exhibited a typical and obvious decline in net photosynthetic rate (PN) during midday, which was not observed in L. aurea. This indicated a possible photoinhibition in L. houdyshelii and L. albiflora as the ratio of variable to maximum fluorescence (Fv/Fm) values were higher in these two species. The minimal fluorescence (F0) values were lower in L. aurea and L. radiata var. pumila. The diurnal changes of transpiration rate (E) in all four species presented only one peak, appearing between 11:00 h or 13:00 h. By using simple correlation analyses, it was observed that the environmental factors affecting
PN were different among four species and the main factors were photosynthetic photon flux density (PPFD) and relative humidity especially for L. aurea and L. radiata. The results of studying indicated that the four species could be divided into two groups. The species L. radiata var. pumila and L. aurea were more adapted to a relatively high irradiance, and L. houdyshelii and L. albiflora could be grown in moderate-shade environment in order to scale up their growth and productivity., K. Liu ... [et al.]., and Obsahuje bibliografii
Leaf tissue damaging to seedlings can limit their subsequent growth, and the effects may be more extensive. Compensatory photosynthesis responses of the remnant cotyledon and primary leaf of Pharbitis purpurea to clipping and the effect of clipping on seedling growth were evaluated in a pot-cultivated experiment. Three treatments were conducted in the experiment, which were clipped cotyledon (CC), clipped second leaf (CL), and control group (CG). The area, thickness, mass, and longevity of the remaining cotyledon of CC exhibited over-compensatory growth. In contrast, seedlings of CC had under-compensatory growth in seedling height, root length, seedling mass, and root to shoot ratio. However, the traits of remnant cotyledon and seedling in CL treatment exhibited equal-compensatory growth. Net photosynthetic rate of the cotyledon of CC was significantly higher than those of CL and CG treatments, and the diurnal changes in photosynthetic rates showed significantly different patterns which were unimodal curve (CC) and bimodal curve (CL and CG), respectively. There was no significant difference between CL and CG treatment. Net photosynthetic rate of the primary leaf of CL was significantly higher than that of CG treatment. However, the photosynthetic rates of primary leaves of CL and CG treatments showed similar photosynthetic patterns characterized by a bimodal curve. P. purpurea seedlings used a compensatory growth strategy in the remaining cotyledon or the primary leaf to resist leaf loss and minimize any adverse effects. and W. Zheng ... [et al.].
The proportional light absorptance by photosynthetic tissue (α) is used with chlorophyll (Chl) fluorescence methods to calculate electron transport rate (ETR). Although a value of α of 0.84 is often used as a standard for calculating ETR, many succulent plant species and species with crassulacean acid metabolism (CAM) have photosynthetic tissues that vary greatly in color or are highly reflective, and could have values of α that differ from 0.84, thus affecting the calculation of ETR. We measured ETR using Chl fluorescence and α using an integrating sphere in 58 plant species to determine the importance of applying a measured value of α when calculating ETR. Values of α varied from 0.55-0.92 with a mean of 0.82 across species. Differences between ETR values calculated with measured α values ranged from 53% lower to 12% greater than ETR values calculated with a standard α value of 0.84 and were significantly different in 39 out of 58 species. While measurements of ETR using Chl fluorescence represent a rapid and effective assessment of physiological performance, the value of α needs to be considered. Measurements of α, especially on species with light-colored or reflective photosynthetic tissue, will allow more accurate determination of photosynthesis in succulent and CAM species. and J. A. Stemke, L. S. Santiago
We compared variation in sun-canopy leaf anatomy, morphology and photosynthetic rates of coexisting woody species (trees and lianas) in an 8-year-old secondary forest (SF) and mature forest (MF) in the wet season in Xishuangbanna, SW China. Variability of leaf traits of 66 species within growth-form groups in each forest was quantified using coefficients of variation (CV). For the mean values, the woody species in the SF had significantly higher leaf thickness and stomatal density, but lower nonmesophyll/mesophyll ratios than those in the MF. The average leaf area and leaf mass area (LMA) in the studied woody species did not change greatly during the successional process, but differed significantly between the growth forms, with trees having higher values than lianas. The light-saturated photosynthetic rate per unit leaf area (Aa) of the woody species in the SF ranged from 11.2 to 34.5 μmol m-2 s-1, similarly to pioneer tree species from literature data in southeast Asia. The Aa and photosynthetic nitrogen-use efficiency (PNUE) were significantly higher than those in the MF; whereas Aa in the MF ranged between 9 to 21 μmol m-2 s-1, with similar values between lianas and trees. For all woody species in both SF and MF, there were no significant differences in the average values of the CV of all measured variables for both lianas and trees. However, considerable variation in leaf anatomy, morphology, and photosynthetic rates within both growth forms and forests existed, as well as substantial variation in leaf size and stomatal density. We concluded that the tropical woody species formed a heterogeneous functional group in terms of leaf morphology and physiology in both secondary and mature forests. and L. Han ... [et al.].
Photosynthetic parameters and leaf carbon isotope composition (δ13C) in contrasting rice genotypes in relation to supplemental nitrogen (N) application and water management during the grain-filling period were compared. The changes in stomatal conductance (gs) and ratio of intercellular to ambient CO2 mole fraction (Ci/Ca) depended on the leaf nitrogen concentration (leaf N) in both ‘Hinohikari’ (temperate japonica genotype) and ‘IR36’ (indica genotype). In ‘Hinohikari’, δ13C reflects photosynthetic gas exchange during the grain-filling period, which is indicated by the significant response of δ13C to leaf N. In contrast, in ‘IR36’ δ13C did not depend on leaf N. This varietal difference in δ13C to leaf N can be attributed to a difference in the timing of leaf senescence. In ‘IR36’, leaf N and photosynthetic parameters decreased more rapidly, indicating earlier senescence and a shorter grain-filling period in comparison with ‘Hinohikari’. The significant increase in shoot dry mass in ‘Hinohikari’ resulting from supplemental N application, compared with nonsignificant effect observed in ‘IR36’, suggests that the timing of senescence in relation to the grainfilling period has a preponderant influence on productivity., S. Shimoda., and Obsahuje bibliografii
As a stress factor, salt induces the phosphorylation of light-harvesting chlorophyll (Chl) a/b proteins (LHCII) in Dunaliella salina. In this study, we found that the salt-induced phosphorylation of LHCII was not affected by phosphatase, and that salt simultaneously regulated both the phosphorylation of LHCII and the expression of genes encoding light-harvesting Chl a/b proteins of photosystem II (lhcb) and the gene encoding Chl a oxygenase (cao) in dark-adapted D. salina. The mRNA accumulation patterns of lhcb and cao were similar, which further affected the size of LHCII and the ratio of Chl a to Chl b. Therefore, we inferred this simultaneous regulation is one of the mechanisms of D. salina to adapt to the high-salinity environment. and W. M. Chen ... [et al.].
Goldspur apple (Malus pumila cv. Goldspur) is one of the main fruit trees planted in semiarid loess hilly areas. The photosynthetic efficiency in leaves of eight-year-old trees were studied under different soil water conditions with a Li-6400 portable photosynthesis system and a Li-Cor1600 portable steady state porometer in order to explore the effects of soil water stress on photosynthesis and the suitable soil water content (SWC) for water-saving irrigation of apple orchards. The results showed that the leaf net photosynthetic rate (P N), transpiration rate (E), water-use efficiency (WUE), stomatal conductance (gs), intercellular CO2 concentration (Ci), and stomatal limiting value (Ls) displayed different threshold responses to soil water variation. When SWC was within a range of about 60%-86% of field capacity (FC), PN and E were maintained in a relative steady state. At an elevated level but below 60% of FC, both PN and E decreased evidently with decreasing soil moisture. The SWC needed to support WUE in a relatively steady state and at a high level was in the range of about 50%-71% of FC. When SWC was less than 48% of FC, g s and Ls declined with decreasing soil moisture, while Ci increased rapidly. Based on the analysis of the stomatal limitation of photosynthesis using two criteria (Ci and Ls) suggested by Farquhar and Sharkey, it was implied that the predominant cause of restricting PN had changed from stomatal limitation to nonstomatal one under severe water stress. In terms of water-saving irrigation for enhancing water-use efficiency, it was concluded that in semiarid loess hilly areas, the suitable range of SWC for water-saving irrigation in goldspur apple orchards is in the range of about 50%-71% of FC, and the most severe degree of soil water stress tolerated for photosynthesis is about 48% of FC. and S. Y. Zhang ... [et al.].
To investigate damaging mechanisms of chilling and salt stress to peanut (Arachis hypogaea L.) leaves, LuHua 14 was used in the present work upon exposure to chilling temperature (4°C) accompanied by high irradiance (1,200 μmol m-2 s-1) (CH), salt stress accompanied by high irradiance (1,200 μmol m-2 s-1) (SH), and high-irradiance stress (1,200 μmol m-2 s-1) at room temperature (25°C) (NH), respectively. Additionally, plants under low irradiance (100 μmol m-2 s-1) at room temperature (25°C) were used as control plants (CK). Relative to CK and NH treatments, both the maximal photochemical efficiency of PSII (Fv/Fm) and the absorbance at 820 nm decreased greatly in peanut leaves under CH and SH stress, which indicated that severe photoinhibition occurred in peanut leaves under such conditions. Initial fluorescence (F0), 1 - qP and nonphotochemical quenching (NPQ) in peanut leaves significantly increased under CH- and SH stress. Additionally, the activity of superoxide dismutase (SOD), one of the key enzymes of water-water cycle, decreased greatly, the accumulation of malondialdehyde (MDA) and membrane permeability increased. These results suggested that damages to peanut photosystems might be related to the accumulation of reactive oxygen species (ROS) induced by excess energy, and the water-water cycle could not dissipate energy efficiently under the stress of CH and SH, which caused the accumulation of ROS greatly. CH and SH had similar damaging effects on peanut photosystems, except that CH has more severe effects. All the results showed that CH- and SH stress has similar damaging site and mechanisms in peanut leaves. and L.-Q. Qin ... [et al.].
The effects of experimental warming on the growth and physiology of grass Elymus nutans and forb Potentilla anserina were studied by using open-top chambers (OTCs) in an alpine meadow of the eastern Tibetan Plateau. The warming treatment increased mean air and soil surface temperatures by 1.53°C and 0.50°C, respectively, but it reduced soil relative water content in the surface layer. Experimental warming enhanced the growth and gas exchange of E. nutans, while it reduced those of P. anserina. Experimental warming resulted in an increased efficiency of photosystem II (PSII) in E. nutans, while decreasing it in P. anserina; significantly stimulated non-photochemical quenching, antioxidative enzymes and non-enzymes in both species; and significantly reduced malondialdehyde content in E. nutans, while promoting it in P. anserina. The results of this study indicated that the two species showed different growth responses to experimental warming and their different physiological performances further indicated that experimental warming alleviated the negative effect of low temperature on the growth and development of E. nutans, but limited the competitive ability of P. anserina in the study region. and F. S. Shi ... [et al.].
The impact of grazing by domestic goats, Capra hircus, on the photochemical apparatus of three co-ocurring Mediterranean shrubs, Erica scoparia, Halimium halimifolium, and Myrtus communis was evaluated. Seasonal course of gas exchange, chlorophyll fluorescence and photosynthetic pigment concentrations were measured in the field in grazed and ungrazed plants. Net photosynthetic rate was higher in grazed plants of E. scoparia and H. halimifolium in May, while there were not significant differences in M. communis. Photosynthetic enhancement in grazed plants of E. scoparia could be explained largely by higher stomatal conductance. On the other hand, the lack of differences in stomatal conductance between grazed and ungrazed plants of
H. halimifolium could indicate that carboxylation efficiency, and ribulose-1,5-bisphosphate (RuBP) regeneration may have been enhanced by grazing. Overall grazing has little effect on the photochemical (PSII) apparatus, however grazed plants of M. communis showed chronic photoinhibition in the short term. Finally, seasonal variations recorded on photosynthesis, photochemical efficiency and pigment concentrations may be a physiological consequence of environmental factors, such as summer drought and competition for light, rather than an adaptation to grazing. and S. Redondo-Gómez ... [et al.].
Leaf stomatal conductance (gs), transpiration rate (E), and light-saturated net photosynthetic rate (PNmax) at three developmental stages (tillering stage, jointing-booting stage, and milking stage) and leaf total nitrogen concentration (LTNC) and δ13C value at milking stage were measured for a conventional rice line (Minghui 63) and its corresponding Bacillus thuringiensis (Bt)-gene [cry1A
(b and c)] introduced line (Bt line) under three fertilizer levels. Compared to conventional line, Bt line showed lower gs, which was associated with lower P Nmax and E, but instantaneous water-use efficiency (WUE), measured as the ratio of PNmax to E, was higher in the Bt line than in the conventional line, particularly in the jointing-booting stage. However, δ13C values were not significantly different across treatments, suggesting that intrinsic water-use efficiency (WUEin) might be indistinguishable between Bt and conventional lines. LTNC was higher but PNmax was lower in Bt line compared to conventional line, resulting in significantly lower photosynthetic nitrogen-use efficiency (PNUE). This might result from the additional cost of producing Bt protein in the Bt line due to the effect of competing nitrogen with photosynthetic machinery. Bt-gene introduction and expression does not significantly change WUEin but may significantly decrease leaf PNUE. Thus we suggest that Bt rice should be carefully examined in relation to environmental risks (e.g. water-body pollution) before planting commercially. and R. Q. Guo ... [et al.].
In eukaryotic oxygenic photosynthetic organisms (both plants and algae), the maximum fluorescence is at peak P, with peak M lying much lower, or being even absent. Thus, the PSMT phase, where S is semisteady state, and T is terminal state, is replaced by a monotonous P→T fluorescence decay. In the present study, we found that dimethoate-treated wheat plant leaves showed SM transient, whereas in the case of control plants monotonous P→T fluorescence decay occured. We suggest that this was partly due to quenching of fluorescence due to [H+], responsible for P to S (T) decay in control plants (Briantais et al. 1979) being replaced by state transition (state 2 to state 1) in dimethoate-treated plants (Kaňa et al. 2012)., J. K. Pandey, R. Gopal., and Obsahuje bibliografii
The Amazonian peach palm (Bactris gasipaes Kunth) has been grown for heart-of-palm production under subtropical conditions. As we did not see any substantial study on its photosynthesis under Amazonian or subtropical conditions, we carried out an investigation on the diurnal and seasonal variations in photosynthesis of peach palms until the first heart-of-palm harvest, considering their relationship with key environmental factors. Spineless peach palms were grown in 80-L plastic pots, under irrigation. Gas exchange and chlorophyll fluorescence emission measurements were taken in late winter, mid spring, mid summer and early autumn, from 7:00 to 18:00 h, with an additional chlorophyll fluorescence measurement at 6:00 h. The highest net CO2 assimilation (PN), observed in mid summer, reached about 15 μmol m-2 s-1, which was about 20% higher than the maximum values found in autumn and spring, and 60% higher than that in winter The same pattern of diurnal course for PN was observed in all seasons, showing higher values from 8:00 to 9:00 h and declining gradually from 11:00 h toward late afternoon. The diurnal course of stomatal conductance (gs) followed the same pattern of
PN, with the highest value of 0.6 mol m-2 s-1 being observed in February and the lowest one (0.23 mol m-2 s-1) in September. The maximal quantum yield of photosystem II (Fv/Fm) was above 0.75 in the early morning in all the months. The reversible decrease was observed around midday in September and October, suggesting the occurrence of dynamic photoinhibition. A significant negative correlation between the leaf-air vapour pressure difference (VPDleaf-air) and PN and a positive correlation between PN and gs were observed. The photosynthesis of peach palm was likely modulated mainly by the stomatal control that was quite sensible to atmospheric environmental conditions. Under subtropical conditions, air temperature (Tair) and VPDleaf-air impose more significant effects over PN of peach palm than an excessive photosynthetic photon flux density (PPFD). The occurrence of dynamic photoinhibition indicates that under irrigation, peach palms appeared to be acclimated to the full-sunlight conditions under which they have been grown. and M. L. S. Tucci ... [et al.].
Diurnal dynamics of photosynthetic character of Angelica sinensis, as well as effect of continuous cropping on leaf photosynthetic character, antioxidant enzyme activity and growth of A. sinensis were investigated under field condition. The results showed that the diurnal net photosynthetic rate of A. sinensis in sunny day exhibited a double-peak pattern, and the peaks occurred at 9:45 and 16:45 h, respectively. There was a significant midday depression with A. sinensis, which was caused principally by stomatal factors such as stomatal conductance. The results also showed that net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), intercellular CO2 concentration (Ci), and chlorophyll content (Chl) of A. sinensis plants under continuous cropping were significantly lower than those of the control. The activity of total superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and growth parameters of A. sinensis plants were significantly decreased under continuous cropping condition. This study provides evidence of continuous cropping obstacle effect on photosynthesis, antioxidant enzyme activity, and growth parameters of A. sinensis in a field experiment, which partly explained the yield reduction of A. sinensis in the field, when it was cultivated continuously on the same soil., X. H. Zhang ... [et al.]., and Obsahuje bibliografii
Drought was induced in chickpea (Cicer arietinum L.) genotypes (ChK 3226 and ILC 3279) differing in yield capacity. Water stress (S1, RWC around 55-50%; S2, RWC ≤ 40%) drastically reduced stomatal conductance (g s) and net photosynthetic rate (PN) in both genotypes. ILC 3279 showed greater photosynthetic capacity
(Amax) decreases. Maximum PSII photochemical efficiency (Fv/Fm), photochemical quenching (qP), total chlorophylls (Chls) and carotenoids (Cars) content showed stability in both genotypes under stress, but in S2 ILC 3279 presented an increase in basal fluorescence (F0) and a greater reduction in estimation of quantum yield of linear electron transport (Φe) than ChK 3226. Membrane damage evaluated by electrolyte leakage occurred earlier and was greater in ILC 3279. It also presented a decrease of total fatty acids (TFA) along drought, while in ChK 3226 greater amounts of TFA were observed in S1. In rehydration, PN of S1 plants completely recovered (ILC 3279) or remained slightly below control (ChK 3226). As regards S2 plants, ILC 3279 showed stronger PN and gs reductions than ChK 3226, despite both genotypes totally recovered Amax and chlorophyll (Chl) a fluorescence. ChK 3226 recovered more efficiently from membrane damage. Under control conditions, greater amounts of most of the studied soluble metabolites occurred in ChK 3226 plants. Malate and citrate decreased with water stress (S2) in both genotypes. Sucrose and pinitol (that had a higher concentration than sucrose in both genotypes) increased in ILC 3279 (S1 and S2), and decreased in ChK 3226 (S2). In ILC 3279 proline and asparagine followed similar patterns. Genotypes showed a similar shoot dry mass (DM) in control plants, but root DM was higher in ChK 3226. Drought reduced root and shoot DM in ChK 3226 already under S1, while in ILC 3279 root DM was unaffected by drought and shoot biomass decreased only in S2. Root/shoot ratio was always higher in ChK 3226 but tended to decrease under stress, while the opposite was observed in ILC 3279. No pods were obtained from control plants of both genotypes, or droughted ILC 3279 plants. ChK 3226 produced pods under S1 (higher yield) and S2. Under stress conditions, ChK 3226 was less affected in photosynthetic activity and membrane integrity, showing a better tolerance to drought. This agrees with the better yield of this genotype under water stress. Distinct strategies seem to underlie the different physiological responses of the two genotypes to water deficit. In spite of its significant solutes accumulation, ILC 3279 was more affected in photosynthetic activity and membrane integrity during water stress than ChK 3226, which showed better yield, under drought. A relation could not be established between solutes accumulation of ILC 3279 and yield., and M. C. Matos ... [et al.].
Global warming will likely exacerbate the negative effects of limited water availability in the Mediterranean area. The Italian Aleppo pine (Pinus halepensis Mill.) provenances are distributed along the coasts except Otricoli provenance growing in an unusual location between 300 and 1,000 m a. s. l., in Umbria (central Italy). The aim of the present study was to investigate the photosynthetic response to a 28-day-long drought and to a subsequent reestablishment of water availability in Otricoli and North Euboea (Greece) provenances, representing different locations along a rainfall gradient in the natural range of this species. Six-month-old seedlings were used in this experiment since at this age Aleppo pine plants in Mediterranean climate face their first water stress potentially affecting plant survival. Water potential (ψw), net photosynthesis and stomatal conductance decreased during drought in both provenances and showed minimal values 28 days after beginning the treatment (DAT). Otricoli seedlings adjusted ψw gradually as the stress level increased and 21 DAT showed a lower ψw than North Euboea. In contrast, in North Euboea seedlings ψw that was not affected until 21 DAT rapidly dropped to a minimum of -3.81 MPa 28 DAT. At the onset of the stress the intercellular CO2 concentration (Ci) was reduced, and the "instrinsic" water-use efficiency (WUEi) was enhanced in both provenances, as stomatal conductance decreased more rapidly than photosynthesis. However, 28 DAT, Ci increased and WUEi decreased as stomatal conductance and photosynthesis declined to minimum levels, revealing nonstomatal limitations of photosynthesis. A rapid decrease in PSII maximal photochemical efficiency estimated by chlorophyll (Chl) fluorescence (Fv/Fm) was also observed when the stress became severe. At the final stage of water stress, North Euboea seedlings maintained significantly higher values of Fv/Fm than Otricoli seedlings. Upon rewatering, photosynthesis did not fully recover in Otricoli seedlings (41 DAT), while all other parameters recovered to control levels in both provenances. No drought-induced physiological differences were consistent with the regional climatic features of these two provenances. Our results suggest that phenotypic plasticity in drought response may help Otricoli provenance cope with global warming, but that recurrent drought episode may slow down the primary productivity of this provenance. and M. Michelozzi ... [et al.].
Plant density, planting time, harvest timing, and nitrogen influence on short-term gas-exchange properties of carrot cultivars, Topcut and Sugarsnax (Daucus carota L.) were investigated under field conditions. Net photosynthetic rate (PN), stomatal conductance
(gs), and transpiration rate (E) differed significantly with the cultivars studied. Both planting and harvest timing changed the midday PN rates. P N increased as harvest timing advanced regardless of planting time. Late planting combined with late harvesting registered the maximum P N rates (4.5 μmol m-2 s-1). The water-use efficiency (WUE) was altered by temperature at different harvest timings along with the choice of cultivar. Early harvested Sugarsnax had a higher WUE (2.29 mmol mol-1) than TopCut (1.64 mmol mol-1) as Sugarsnax exhibited more stomatal conductance than TopCut. These changes were principally governed by fluctuations observed with air temperature and photosynthetic photon flux density (PPFD) and altered by the sensitivity of the cultivars to ecological factors. Plant density did not affect the photosynthetic gas-exchange parameters. Our results suggest that carrots manage high population density solely through morphological adaptations with no photosynthetic adjustments. Carrot leaves responded to N application in a curvilinear fashion in both cultivars. N did not alter gs, E, or WUE in carrots. N, applied at a rate of 150 kg N ha-1, increased foliar N up to 2.98%. We conclude that 2.98% of foliar N is sufficient to achieve the maximum photosynthetic rates in processing carrots., A. Thiagarajan, R. Lada, A. Adams., and Obsahuje bibliografii
Phosphorus (P) is one of the limiting mineral nutrient elements in the typical steppe of Inner Mongolia, China. In order to find out the adaptive strategy of Caragana microphylla to low soil P status, we grew plants in P-deficient soil in April 2009 and gave a gradient of P addition ranging from 0 to 60 mg(P) kg-1(soil) from May 2010. Leaf traits were measured in September 2010. Both leaf growth and light-saturated photosynthetic rate (P max) were similar among different groups. Leaf nitrogen (N):P ratio indicated that the growth of C. microphylla was not P-limited in most of the Inner Mongolia typical steppe, which had an average soil available P content equal to 3.61 mg kg-1. The optimal P addition was 20 mg(P) kg-1(soil) for two-year-old plants of C. microphylla. Leaf mass area (LMA) and leaf dry matter content (LDMC) were enhanced with low P, and significantly negatively correlated with photosynthetic N-use efficiency (PNUE). Photosynthetic P-use efficiency (PPUE) increased with decreasing soil P and increasing leaf inorganic
P (Pi): organic P (Po) ratio, and showed no significant negative correlation with LMA or LDMC. P max of C. microphylla did not decline so sharply as it was anticipated. The reason for this phenomenon might be due to the increased PPUE through regulating the leaf total P allocation. C. microphylla had high P-use efficiency via both high PPUE and long P-retention time at low-P supply. The adaptation of C. microphylla to low-P supply provided a new explanation for the increased distribution of the species in the degraded natural grassland in Inner Mongolia, China., T. T. Zhao, N. X. Zhao, Y. B. Gao., and Obsahuje bibliografii
Caragana korshinskii Kom. is a perennial xerophytic shrub, well known for its ability to resist drought. In order to study ecophysiological responses of C. korshinskii under extreme drought stress and subsequent rehydration, diurnal patterns of gas exchange and chlorophyll (Chl) fluorescence parameters of photosystem II as well as Chl content were analyzed. Plant responses to extreme drought included (1) leaf abscission and using stem for photosynthesis, (2) improved instantaneous water-use efficiency, (3) decreased photosynthetic rate and partly closed stomata owing to leaf abscission and low water status, (4) decreased maximum photochemical efficiency of photosystem II (PSII) (variable to maximum fluorescence ratio, Fv/Fm), quantum efficiency of noncyclic electron transport of PSII, and Chl a and Chl b. Four days after rehydration, new leaves budded from stems. In the rewatered plants, the chloroplast function was restored, the gas exchange and Chl fluorescence returned to a similar level as control plant. The above result indicated that maintaining an active stem system after leaf abscission during extreme drought stress may be the foundation which engenders these mechanisms rapid regrowth for C. korshinskii in arid environment., D. H. Xu ... [et al.]., and Obsahuje bibliografii
A mixture of ryegrass (Lolium italicum A. Braun) and clover (Trifolium alexandrinum L.) was sown in Eboli (Salerno, Southern Italy) in September 2007. Crop growth, leaf and canopy gas exchange and ecophysiological traits were monitored throughout the growth cycle. The gross primary production (GPP) was not affected by air temperature (T air); on the contrary the ecosystem respiration (R eco) decreased as T air decreased while net ecosystem CO2 exchange (NEE) increased. When was normalized with leaf area index (LAI), GPP decreased with T air, a likely response to cold that down-regulated canopy photosynthesis in order to optimize the light use at low winter temperatures. Net photosynthetic rates (PN), the effective quantum yield of PSII (ΦPSII) and photosynthetic pigment content were higher in clover than ryegrass, in relation to the higher leaf N content. The lower ΦPSII in ryegrass was linked to lower photochemical quenching coefficient (qP) values, due to a reduced number of reaction centres, in agreement with the lowest Chl a content. This behaviour can be considered as an adaptive strategy to cold to avoid photooxidative damage at low temperature rather than an impairment of PSII complexes., L. Vitale ... [et al.]., and V klíčových slovech chybně uvedené jméno Lolium italicum A. Barum
Excessive levels of bicarbonate adversely affect the growth and metabolism of plants. Broussonetia papyrifera (L.) Vent. and Morus alba L., belonging to family Moraceae, possess the favorable characteristics of rapid growth and adaptability to adverse environments. We examined the response of these two plant species to bicarbonate stress in terms of photosynthetic assimilation of inorganic carbon. They were exposed to 10 mM sodium bicarbonate in the culture solution for 20 days. The photosynthetic response was determined by measuring the net photosynthetic rate of the leaf, water-use efficiency, and chlorophyll fluorescence on days 10 and 20. The bicarbonate-use capacity of the plants was studied by measuring the carbonic anhydrase activity and the compositions of the stable carbon and hydrogen isotopes. The photosynthetic response to high concentration of bicarbonate varied with plant species and treatment durations. High concentrations of bicarbonate decreased the photosynthetic assimilation of inorganic carbon in the two plant species to half that in the control plants on day 10. Bicarbonate treatment did not cause any damage to the reaction centers of photosystem II in Morus alba; it, however, caused a decline in the quantum efficiency of photosystem II in B. papyrifera on day 20. Moreover, B. papyrifera had a greater bicarbonate-use capacity than M. alba because carbonic anhydrase converted bicarbonate to CO2 and H2O to a greater extent in B. papyrifera. This study showed that the effect of bicarbonate on photosynthetic carbon metabolism in plants was dual. Therefore, the concentration of bicarbonate in the soil should first be considered during afforestation and ecological restoration in karst areas., Y. Y. Wu, D. K. Xing., and Obsahuje bibliografii
The aim of the study was to the assess the influence of Ca/Mg ions ratio on the photosynthetic activity of Salix viminalis L. ‘Cannabina’ plants cultivated in medium enriched with Cu(NO3)2. The experiment was conducted in controlled conditions in a phytotron for 21 days; hence the early plant response was tested. Plants were cultivated with different Ca/Mg ions ratios, i.e. (4:1)l, (4:1)h, and 1:10. Plants were additionally treated with Cu(NO3)2 at 1, 2, and 3 mM concentration in cultivation medium. Net photosynthetic rate, stomatal conductance and transpiration were measured after the first, second and third week of cultivation. Additionally, chlorophyll content, leaf morphology, root biomass and copper accumulation in leaves and roots were investigated. The investigations revealed differences in plant response to particular treatments - differences in Cu accumulation for particular Ca/Mg ions ratios were detected. It seems that plants are adapted to high Cu2+ concentrations, when 1:10 Ca/Mg ions ratio is applied. The highest Cu accumulation in roots was noted for plants fertilized with 1:10 Ca/Mg ions ratio, together with high Cu translocation to above-ground plant organs, which suggests its higher potential in phytoremediation., K. Borowiak ... [et al.]., and Obsahuje bibliografii
The use of Jatropha curcas oil as a source of biofuel has been well-explored. However, the physiological and growth studies of J. curcas have received considerably lesser attention. In this study, leaf gas exchange measurements and leaf nitrogen content were determined for four varieties of J. curcas, grown in the field or in pots. Based on stable carbon isotope analysis (δ13C) and
gas-exchange studies, J. curcas is a C3 sun plant and the range of leaf photosynthetic rates (or CO2 assimilation rates, PNmax) were typically between 7 and 25 μmol(CO2) m-2 s-1 and light saturation generally occurred beyond 800 μmol(quanta) m-2 s-1. Higher rates of leaf photosynthesis were generally obtained with the mature leaves. In addition, increased foliar PNmax were recorded in potted J. curcas variety Indiana with increasing nitrogen (N) nutrition levels. These plants also showed greater growth, increased leaf N content, higher maximum CO2 assimilation capacity (PNhighCO2) and chlorophyll (Chl) content, indicating the potential of optimizing the growth of Jatropha by varying fertilizer nutrient levels. A rapid assessment for leaf N using a nondestructive and portable Chl meter had been established for J. curcas. This approach will allow repeated sampling of the same plant over time and thus enable the monitoring of the appropriate levels of soil fertility to achieve good Jatropha plantation productivity. High N nutrition improved the overall plant oil yield by increasing the total number of fruits/seeds produced per plant, while not affecting the intrinsic seed oil content. and J. W. H. Yong ... [et al.].
The present study was undertaken to investigate the effect of Glomus mosseae on chlorophyll (Chl) content, Chl fluorescence parameters and chloroplast ultrastructure of beach plum seedlings under 2% NaCl stress. The results showed that compared to control, both Chl a and Chl b contents of NaCl + G. mosseae treatment were significantly lower during the salt stress, while Chl a/b ratio increased significantly. The increase of minimal fluorescence of darkadapted state (F0), and the decrease of maximal fluorescence of dark-adapted state (Fm) and variable fluorescence (Fv) values were inhibited. The maximum quantum yield of PSII photochemistry (Fv/Fm), the maximum energy transformation potential of PSII photochemistry (Fv/F0) and the effective quantum yield of PSII photochemistry (ΦPSII) increased significantly, especially the latter two variables. The values of the photochemical quenching coefficient (qP) and the nonphotochemical quenching (NPQ) were similar between G. mosseae inoculation and noninoculation. It could be concluded that G. mosseae inoculation could protect the photosystem II (PSII) of beach plum, enhance the efficiency of primary light energy conversion and improve the primitive response of photosynthesis under salinity stress. Meanwhile, G. mosseae inoculation was beneficial to maintain the integrity of thylakoid membrane and to protect the structure and function of chloroplast, which suggested that G. mosseae can alleviate the damage of NaCl stress to chloroplast., X. M. Zai ... [et al.]., and Obsahuje bibliografii
Mosses are plants of simple anatomical structure and as they occur in habitats characterised not only by major changes in the concentrations of carbon dioxide, they suffer the stress of periodic water shortages or submergence in water. The condition of hypoxia (submergence in water or CaCl2 solution) prompted the increase in daily fluctuations in malate content, particularly in the gametophores of Polytrichum piliferum Hedw. No significant increases in daily fluctuations of citrate were found in the hypoxia and post-hypoxia conditions. Placing gametophores for 168 h in air with a concentration of CO2 at ∼ 350 μmol mol-1, and 21% of oxygen, after being submerged for 24 h in water, reduced the daily fluctuations of malate and citrate. Keeping the plants in these conditions for a long time (120-168 h) produced the increase in photosynthesis intensity in the gametophores of Mnium undulatum Hedw. and P. piliferum by 13% and 51%, respectively, when compared with plants submerged for 24 h. The intensity of respiration during post-hypoxia, however, was markedly lower compared with the intensity of the process recorded in hypoxia, particularly in the gametophores of P. piliferum. The increased daily fluctuations of malate and NAD(P)H in the studied species under hypoxia could constitute an important element of adaptive strategy to these conditions. and G. Rut, A. Rzepka, J. Krupa.
The effects of soil salt-alkaline (SA) stress on leaf physiological processes are well studied in the laboratory, but less is known about their effect on leaf, bark and branch chlorenchyma and no reports exist on their effect on C4 enzymes in field conditions. Our results demonstrated that activities of C4 enzymes, such as phospholenolpyruvate carboxylase (PEPC), NADP-malic enzyme (NADP-ME), pyruvate orthophosphate dikinase (PPDK), and NADP-dependent malate dehydrogenase (NADP-MDH), could also be regulated by soil salinity/alkalinity in poplar (Populus alba × P. berolinensis) trees, similarly as the already documented changes in activities of antioxidative enzymes, such as superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR), pigment composition, photosynthesis, and respiration. However, compared with 50-90% changes in a leaf and young branch chlorenchyma, much smaller changes in malondialdehyde (MDA), antioxidative enzymes, and C4 enzymatic activities were observed in bark chlorenchyma, showing that the effect of soil salinity/alkalinity on enzymatic activities was organ-dependent. This suggests that C4 enzymatic ratios between nonleaf chlorenchyma and leaf (the commonly used parameter to discern the operation of the C4 photosynthetic pathway in nonleaf chlorenchyma), were dependent on SA stress. Moreover, much smaller enhancement of these ratios was seen in an improved soil contrary to SA soil, when the fresh mass (FM) was used as the unit compared with a calculation on a chlorophyll (Chl) unit. An identification of the C4 photosynthesis pathway via C4 enzyme difference between chlorenchyma and leaf should take this environmental regulation and unit-based difference into account., H. M. Wang ... [et al.]., and Obsahuje bibliografii
Shoots of the tropical latex-producing tree Hevea brasiliensis (rubber tree) grow according to a periodic pattern, producing four to five whorls of leaves per year. All leaves in the same whorl were considered to be in the same leaf-age class, in order to assess the evolution of photosynthesis with leaf age in three clones of rubber trees, in a plantation in eastern Thailand. Light-saturated CO2 assimilation rate (Amax) decreased more with leaf age than did photosynthetic capacity (maximal rate of carboxylation, Vcmax , and maximum rate of electron transport, Jmax), which was estimated by fitting a biochemical photosynthesis model to the CO2-response curves. Nitrogen-use efficiency (Amax/Na, Na is nitrogen content per leaf area) decreased also with leaf age, whereas Jmax and
Vcmax did not correlate with Na. Although measurements were performed during the rainy season, the leaf gas exchange parameter that showed the best correlation with Amax was stomatal conductance (gs). An asymptotic function was fitted to the Amax-gs relationship, with R2 = 0.85. Amax, Vcmax, Jmax and gs varied more among different whorls in the same clone than among different clones in the same whorl. We concluded that leaf whorl was an appropriate parameter to characterize leaves for the purpose of modelling canopy photosynthesis in field-grown rubber trees, and that stomatal conductance was the most important variable explaining changes in Amax with leaf age in rubber trees. and B. Kositsup ... [et al.].
In a greenhouse experiment, the influence of arbuscular mycorrhizal fungi (Glomus mosseae and Glomus intraradices) and water stress [100% field capacity (FC), 75% FC, 50% FC and 25% FC] on maximal quantum yield of photosystem II (PSII) photochemistry (Fv/Fm) and some other ecophysiological characteristics of two pistachio cultivar (Pistacia vera cv.
Badami-Riz-Zarand and Pistacia vera cv. Qazvini) were investigated.
No difference was found in colonization rate between the two arbuscular mycorrhizal fungi (AMF) applied. Water stress reduced the mycorrhizal colonization in both cultivars at the same rate but the difference was significant just with severe water stress level (25% FC). The Fv/Fm was also adversely affected by water stress from 75% FC downwards in Qazvini cultivar while in Badami, increase in water-stress intensity had no significant effect on this parameter. Gasexchange parameters were decreased with increasing stress intensity and chlorophyll (Chl) pigments were increased with mild water stress (75% FC) compared with control (100% FC) and then decreased with increasing stress intensity. The carotenoids (Car) content increased significantly in the stressed leaves in all water-stress levels irrespective of AMF treatment and cultivar type.
The adverse effects of water stress were significantly reduced by AM inoculation and in the most of measured parameters, both AMF had an equal influence except with the intercellular CO2 concentration (Ci), where G. intraradices was superior. Results obtained from Chl fluorescence probe indicated that inoculated AMF enhanced photochemical efficiency of light reactions of the PSII in intact pistachio leaf tissues both under irrigation and waterstress conditions. Under mild and moderate water stress, mycorrhizal pistachio plants had higher relative Chl and Car content and higher gas-exchange capacity (increased photosynthesis and transpiration rate) but under severe water-stress condition (25% FC), the effects of mycorrhizal treatments were not noticeable. Data obtained in present study emphasized that Qazvini is more tolerant to water stress than Badami because photosynthesis activity in Qazvini was more efficiently protected than in the Badami, as indicated by related parameters. and V. Bagheri ... [et al.].
To examine the role of sink size on photosynthetic acclimation under elevated atmospheric CO2 concentrations ([CO2]), we tested the effects of panicle-removal (PR) treatment on photosynthesis in rice (Oryza sativa L.). Rice was grown at two [CO2] levels (ambient and ambient + 200 μmol mol-1) throughout the growing season, and at full-heading stage, at half the plants, a sink-limitation treatment was imposed by the removal of the panicles. The PR treatment alleviated the reduction of green leaf area, the contents of chlorophyll (Chl) and Rubisco after the full-heading stage, suggesting delay of senescence. Nonetheless, elevated [CO2] decreased photosynthesis (measured at current [CO2]) of plants exposed to the PR treatment. No significant [CO2] × PR interaction on photosynthesis was observed. The decrease of photosynthesis by elevated [CO2] of plants was associated with decreased leaf Rubisco content and N content. Leaf glucose content was increased by the PR treatment and also by elevated [CO2]. In conclusion, a sink-limitation in rice improved N status in the leaves, but this did not prevent the photosynthetic down-regulation under elevated [CO2]. and H. Shimono ... [et al.].
The partial shading effect on the photosynthetic apparatus of the sunflower (Helianthus annuus L.) was examined by monitoring oxygen evolution, maximum quantum yield of PSII photochemistry in dark-adapted leaves (Fv/Fm), the chlorophyll (Chl) concentrations and the Rubisco contents, and leaf mass per area (LMA) at the leaf level and by determining the concentrations of cytochrome (Cyt) f and the reaction centres of photosystem (PS) I and PSII at the thylakoid level. In this experiment, partial shading was defined as the shading of 2nd leaves with shade cloths, and the whole treatment was defined as the covering of the whole individuals with shade cloths. In the leaf level responses, oxygen evolution, LMA, Chl concentrations and Rubisco contents decreased in all shade treatments administered for six days. Fv/Fm remained constant irrespective of the shade treatments. On the other hand, in the thylakoid-level responses, the concentrations of the thylakoid components per unit Chl and the stoichiometry of the two photosystems showed no statistical difference among the shade treatments. The data obtained from the present study indicate that the partial shading affected the leaf-level responses rather than the thylakoid-level responses. The light received at the lower leaves might serve as a factor in the regulation of the leaf properties of the upper leaves due to the whole plant photosynthesis, while this factor did not have an effect at the thylakoid level., J. Ymazaki, Y. Shinomiya., and Obsahuje bibliografii
Soil salinity is one of the most severe factors limiting growth and physiological response in Raphanus sativus. In this study, the possible role of plant growth promoting bacteria (PGPB) in alleviating soil salinity stress during plant growth under greenhouse conditions was investigated. Increasing salinity in the soil decreased plant growth, photosynthetic pigments content, phytohormones contents (indole-3-acetic acid, IAA and gibberellic acid, GA3) and mineral uptake compared to soil without salinity. Seeds inoculated with Bacillus subtilis and Pseudomonas fluorescens caused significantly increase in fresh and dry masses of roots and leaves, photosynthetic pigments, proline, total free amino acids and crude protein contents compared to noninoculated ones under salinity. The bacteria also increased phytohormones contents (IAA and GA3) and the contents of N, P, K+, Ca2+, and Mg2+ but decreased ABA contents and Na+ and Cl- content which may contribute in part to activation of processes involved in the alleviation of the effect of salt., H. I. Mohamed, E. Z. Gomaa., and Obsahuje bibliografii
An experiment was conducted to study the effect of NaCl (electric conductivity of 0, 4, 8, 12, and 16 dS m-1) on growth, gas exchange parameters, water status, membrane injury, chlorophyll stability index and oxidative defense mechanisms in two cultivars (Gola and Umran) of Indian jujube (Ziziphus mauritiana). Results showed that the dry mass and leaf area reduced linearly with increasing levels of salinity. Net photosynthetic rate (PN), transpiration (E), and stomatal conductance (gs) were comparatively lower in Umran which further declined with salinity. Leaf relative water content, chlorophyll (Chl) stability and membrane stability also decreased significantly under salt stress, with higher magnitude in Umran. Superoxide dismutase (SOD), peroxidase (POX) and catalase (CAT) activities were higher in Gola whereas hydrogen peroxide (H2O2) accumulation and lipid peroxidation (MDA content) were higher in control as well as salttreated plants of Umran. The Na+ content was higher in the roots of Gola and in the leaves of Umran, resulting in high K+/Na+ ratio in Gola leaves. Thus it is suggested that salt tolerance mechanism is more efficiently operative in cultivar Gola owing to better management of growth, physiological attributes, antioxidative defense mechanism, and restricted translocation of Na+ from root to leaves along with larger accumulation of K+ in its leaves., R. Agrawal ... [et al.]., and Obsahuje bibliografii
Kappaphycus alvarezii is a seaweed of great economic importance for the extraction of kappa carrageenan from its cell walls. The most common strains are dark red, brown, yellow, and different gradations of green. It is known that ultraviolet radiation (UVR) affects macroalgae in many important ways, including reduced growth rate, reduction of primary productivity, and changes in cell biology and ultrastructure. Therefore, we examined the brown strain of K. alvarezii exposed to ultraviolet-B radiaton (UVBR) for 3 h per day during 28 days of cultivation. The control plants showed growth rates of 7.27% d-1, while plants exposed to UVBR grew only 4.0% d-1. Significant differences in growth rates and in phycobiliproteins between control and exposed plants were also found. Compared with control plants, phycobiliprotein contents were observed to decrease after UV-B exposure. Furthermore, the chlorophyll a (Chl a) contents decreased and showed significant differences. UVBR also caused changes in the ultrastructure of cortical and subcortical cells, which included increased thickness of the cell wall and number of plastoglobuli, reduced intracellular spaces, changes in the cell contour, and destruction of chloroplast internal organization. Reaction with Toluidine Blue showed an increase in the thickness of the cell wall, and Periodic Acid-Schiff stain showed a decrease in the number of starch grains. By the significant changes in growth rates, photosynthetic contents and ultrastructual changes observed, it is clear that UVBR negatively affects intertidal macroalgae and, by extension, their economic viability. and É. C. Schmidt ... [et al.].
The current concentrations of O3 have been shown to cause significant negative effects on crop yield. The present levels of ozone may not induce visible symptoms in most of plants, but can result in substantial losses in reproductive output. This paper considers the impact of ambient O3 on gas exchange, photosynthetic pigments, chlorophyll (Chl) fluorescence and carbohydrate levels in the flag leaf of wheat plants during various stages of reproductive development using open-top chambers. Mean O3 concentration was 45.7 ppb during wheat growth and 50.2 ppb after flag leaf development. Reproductive stage showed higher exceedence of O3 above 40 ppb compared to the vegetative stage. Diurnal variations in net photosynthetic rate (PN) and stomatal conductance (gs), intercellular CO2 concentration (Ci), Fv/Fm ratio, photosynthetic pigments, soluble sugars, and starch were measured at 10, 30, and 50 days after flag leaf expansion (DAFE). The results showed reductions in PN, gs, Fv/Fm ratio, photosynthetic pigments and starch, and increases in Ci, F0, and soluble sugars in nonfiltered chambers (NFCs) compared to filtered chambers (FCs). Maximum changes in measured parameters were observed at 50 DAFE (i.e. grain filling and setting phase). Diurnal variation in PN showed double peaked curve in both FCs and NFCs, but delayed peak and early depression in NFCs. Stomatal conductance was significantly lower in NFCs. The study suggests that higher prevalence of ambient O3 during reproductive development led to significant alteration in physiological vitality of wheat having potential negative influence on yield. and R. Rai, M. Agrawal, S. B. Agrawal.
Most plants growing in temperate desert zone exhibit brief temperature-induced inhibition of photosynthesis at midday in the summer. Heat stress has been suggested to restrain the photosynthesis of desert plants like Alhagi sparsifolia S. It is therefore possible that high midday temperatures damage photosynthetic tissues, leading to the observed inhibition of photosynthesis. In this study, we investigated the mechanisms underlying heat-induced inhibition of photosynthesis in A. sparsifolia, a dominant species found at the transition zone between oasis and sandy desert on the southern fringe of the Taklamakan desert. The chlorophyll (Chl) a fluorescence induction kinetics and CO2 response curves were used to analyze the thermodynamic characters of both photosystem II (PSII) and Rubisco after leaves were exposed to heat stress. When the leaves were heated to temperatures below 43°C, the initial fluorescence of the dark-adapted state (Fo), and the maximum photochemical efficiency of PSII (Fv/Fm), the number of active reaction centers per cross section (RCs) and the leaf vitality index (PI) increased or declined moderately. These responses were reversed, however, upon cooling. Moreover, the energy allocation in PSII remained stable. The gradual appearance of a K point in the fluorescence curve at 48°C indicated that higher temperatures strongly impaired PSII and caused irreversible damage. As the leaf temperature increased, the activity of Rubisco first increased to a maximum at 34°C and then decreased as the temperature rose higher. Under high-temperature stress, cell began to accumulate oxidative species, including ammoniacal nitrogen, hydrogen peroxide (H2O2), and superoxide (O2 .-), suggesting that disruption of photosynthesis may result from oxidative damage to photosynthetic proteins and thylakoid membranes. Under heat stress, the biosynthesis of nonenzyme radical scavenging carotenoids (Cars) increased. We suggest that although elevated temperature affects the heat-sensitive components comprising of PSII and Rubisco, under moderately high temperature the decrease in photosynthesis is mostly due to inactivation of dark reactions. and W. Xue ... [et al.].
We investigated the effect of enhanced atmospheric ammonia (NH3) in combination with low and high nitrogen (LN and HN, respectively) growth medium on photosynthetic characteristics of two maize (Zea mays L.) cultivars (NE5 with high- and SD19 with low N-use efficiency) across long-term growth period and their diurnal change patterns exposed to 10 nl l-1 and 1,000 nl l-1 NH3 fumigation in open-top chambers (OTCs). Regardless of the level of N in medium, increased NH3 concentration promoted maximum net photosynthetic rate (Pmax) and apparent quantum yield (AQY) of both cultivars at earlier growth stages, but inhibited Pmax of NE5 from silking to maturity stage and that of SD19 at maturity stage only above the ambient concentration. Greater positive/less negative responses were predominant in the LN than in the HN treatment, especially for SD19. Dark respiration rate (RD) remained more enhanced in the LN than in the HN treatment for SD19 as well as increased in the LN while decreased in the HN treatment for NE5 at their silking stage, following exposure to elevated NH3 concentration. Additionally, enhanced atmospheric NH3 increased net photosynthetic rate (PN) and stomatal conductance (gs) but reduced intercellular CO2 concentration (Ci) of both cultivars with either the LN or HN treatment during the diurnal period at tasseling stage. The diurnal change patterns of PN and gs showed bimodal curve type and those of Ci presented single W-curve type for NE5, when NH3 concentration was enhanced. As for SD19, single-peak curve type was showed for both PN and gs while single V-curve type for Ci. All results supported the hypothesis that appropriately enhanced atmospheric NH3 can increase assimilation of CO2 by improving photosynthesis of maize plant, especially at earlier growth stages and after photosynthetic "noon-break" point. These impacts of elevated NH3 concentration were more beneficial for SD19 as compared to those for NE5, especially in the LN supply environment. and L. X. Zhang ... [et al.].
The objective of this study was to investigate the effect of elevated (550 ± 17 μmol mol-1) CO2 concentration ([CO2]) on leaf ultrastructure, leaf photosynthesis and seed yield of two soybean cultivars [Glycine max (L.) Merr. cv. Zhonghuang 13 and cv. Zhonghuang 35] at the Free-Air Carbon dioxide Enrichment (FACE) experimental facility in North China. Photosynthetic acclimation occurred in soybean plants exposed to long-term elevated [CO2] and varied with cultivars and developmental stages. Photosynthetic acclimation occurred at the beginning bloom (R1) stage for both cultivars, but at the beginning seed (R5) stage only for Zhonghuang 13. No photosynthetic acclimation occurred at the beginning pod (R3) stage for either cultivar. Elevated [CO2] increased the number and size of starch grains in chloroplasts of the two cultivars. Soybean leaf senescence was accelerated under elevated [CO2], determined by unclear chloroplast membrane and blurred grana layer at the beginning bloom (R1) stage. The different photosynthesis response to elevated [CO2] between cultivars at the beginning seed (R5) contributed to the yield difference under elevated [CO2]. Elevated [CO2] significantly increased the yield of Zhonghuang 35 by 26% with the increased pod number of 31%, but not for Zhonghuang 13 without changes of pod number. We conclude that the occurrence of photosynthetic acclimation at the beginning seed (R5) stage for Zhonghuang 13 restricted the development of extra C sink under elevated [CO2], thereby limiting the response to elevated [CO2] for the seed yield of this cultivar., X. Y. Hao ... [et al.]., and Obsahuje bibliografii
Abscisic acid (ABA), an important chemical signal from roots, causes physiological changes in leaves, including stomata closure and photoprotection. Furthermore, endogenous ABA concentration in leaves and stomatal behavior vary with the species adapted to different water regimes. In this study, Ficus microcarpa, a hemiepiphyte, Salix warburgii, a hygrophyte, and Acacia confusa, a mesophyte, were used to elucidate the effects of leaf detachment on photosystem II (PSII) efficiency under osmotic- and high-light stresses. Results indicate that, under osmotic- and high-light stresses, PSII efficiency of the detached leaves was lower than that of the attached leaves for all three tree species, when compared at the same levels of stomatal resistance and leaf water potential. Exogenous ABA could mitigate the PSII efficiency decrease of detached F. microcarpa leaves under osmotic- and high-light stresses. Yet, the osmotic stress could raise endogenous ABA concentration in the attached, but not in the detached F. microcarpa leaves. In addition, partial root-zone drying exerted a significant effect on stomatal behavior but not on the water status of F. microcarpa leaves. These observations imply that the stronger ability of PSII in the attached leaves of F. microcarpa under osmoticand high-light stresses was probably due to the protective action of ABA from roots. On the contrary, endogenous ABA level of S. warburgii leaves was very low. In addition, partial root-zone drying produced no significant effect on its stomatal behavior. Therefore, PSII in attached S. warburgii leaves was possibly protected from the damaging effects of excess absorbed energy by signals other than ABA, which were transported from the roots. and J.-H. Weng ... [et al.].
Little is known about the response of trees to elevated ozone (O3) in the subtropical region of China, where ambient O3 concentrations are high enough to damage plants. In this study, pigment content, gas exchange and chlorophyll (Chl) a fluorescence in leaves of Liriodendron chinense (Hemsl.) Sarg seedlings, a deciduous broadleaf tree species native in subtropical regions, were investigated at 15, 40, and 58 days after O3 fumigation (DAF) at a concentration of 150 mm3 m-3 (E-O3). At the end of experiment, seedlings were harvested for biomass measurement. E-O3 caused visible injuries on the mature leaves e.g. necrotic patches and accelerated early defoliation. Relative to the charcoal-filtered air (CF) treatment, E-O3 significantly decreased shoot and root biomass, pigment content, light-saturated net photosynthesis (P Nsat), stomatal conductance (gs), maximum rate of carboxylation (Vcmax), photochemical quenching coefficient (qp) and effective quantum yield of PSII photochemistry (ΦPSII), and also caused a slight reduction in relative increase of basal diameter. Therefore, L. chinense can be assumed to be an O3-sensitive tree species, which will be threatened by increasing ambient O3 concentrations in China. and W. W. Zhang ... [et al.].
Several studies have found the photosynthetic integration in clonal plants to response to resource heterogeneity, while little is known how it responses to heterogeneity of UV-B radiation. In this study, the effects of heterogeneous UV-B radiation (280-315 nm) on gas exchange and chlorophyll fluorescence of a clonal plant Trifolium repens were evaluated. Pairs of connected and severed ramets of the stoloniferous herb T. repens were grown under the homogeneity (both of ramets received only natural background radiation, ca. 0.6 kJ m-2 d-1) and heterogeneity of UV-B radiation (one of the ramet received only natural background radiation and the other was exposed to supplemental UV-B radiation, 2.54 kJ m-2 d-1) for seven days. Stomatal conductance (g s), intercellular CO2 concentration (Ci) and transpiration rate (E) showed no significant differences in connected and severed ramets under homogenous and heterogeneous UV-B radiation, however, net photosynthetic rate (PN) and maximum photosynthetic rate (Pmax) of ramets suffered from supplemental increased UV-B radiation and that of its connected sister ramet decreased significantly. Moreover, additive UV-B radiation resulted in a notable decrease of the minimal fluorescence of dark-adapted state (F0), the electron transport rate (ETR) and photochemical quenching coefficient (qP) and an increase of nonphotochemical quenching (NPQ) under supplemental UV-B radiation, while physiological connection reverse the results. In all, UV-B stressed ramets could benefit from unstressed ramets by physiological integration in photosynthetic efficiency, and clonal plants are able to optimize the efficiency to maintain their presence in less favourable sites. and Q. Li ... [et al.].
The effects of postharvest pretreatments on vase life, keeping quality and carbohydrate concentrations in cut sweet pea (Lathyrus odoratus L.) flowers were investigated. Compared to the control, all treatments promoted floret quality and extended longevity. The cut flowers held in the solution containing sucrose + 8-hydroxyquinoline (Suc+HQS) was more effective in promoting absorption rate, achieved greater maximum fresh mass, had better water balance for a longer period, extended the vase life (up to 17 d), and delayed degradation of chlorophylls. The same treatment also enhanced the concentration of soluble carbohydrates in the petals and stems and leaf chlorophyll (Chl) content, whereas it was lowest in silver thiosulphate (STS) treatment. However, concentrations of anthocyanin in the petals were higher for treatment with sucrose or STS plus sucrose than in control or STS alone treatments. Our results suggest that pulse treatment with HQS plus sucrose for 12 h is the most effective for improving pigmentation and use as a commercial cut flower preservative solution to delay flower senescence, enhance quality, and prolong the vase life of sweet pea. The results also showed that soluble carbohydrate concentration in petals and stems is an important factor in determining the vase life of sweet pea flowers., K. M. Elhindi., and Obsahuje bibliografii
An indoor sun simulator was used to provide elevated UV-B radiation (280-315 nm) in combination with realistic ratios to PAR (400-700 nm) and UV-A radiation (315-400 nm) in order to test the physiological response of a soil- and snow microalga during a three-day stress scenario, which may occasionally occur in their respective arctic and alpine habitats.
Chlamydomonas nivalis and Tetracystis sp. are initial colonizers of harsh habitats like summer snow fields and bare arctic soils. The two species were chosen because of their role as primary successors in places where life is generally limited by extreme climatic and nutritional conditions.
The influence of the increased UV-B irradiation (1.43 W m-2; control: 0.52 W m-2) on photosynthesis and pigment composition was measured. Both species survived this incubation without any morphological signs of damage, but oxygen production was reduced by 20-56%. Under control conditions, the amount of chlorophylls (Chls) and carotenoids (Cars) per dry mass increased after three days due to optimal light conditions. After the same period, the treated samples of the soil alga Tetracystis sp. showed a smaller increase in Chls and primary Cars than the control. However, the production of extraplastidal, secondary Cars was induced. On the contrary, the snow alga C. nivalis already had high amounts of secondary Cars before the experiment, and after exposure, all pigment classes increased more compared to control conditions. The results show that these microalgae can tolerate short episodes of enhanced UV-B radiation. Photosynthesis may be temporally impaired, but the cells respond by the production of secondary Cars, which can shield their chloroplasts against excessive irradiation or quench reactive oxygen species. and D. Remias, A. Albert, C. Lütz.
a1_The effect of a wide range of temperatures (-15 and 60°C) in darkness or under strong irradiation [1,600 μmol(photon) m-2 s-1] on quantum yield of photosystem II photochemistry and xanthophyll cycle pigments was investigated in a tropical fruit crop (Musa sp.) and a temperate spring flowering plant (Allium ursinum L.). In darkness within the nonlethal thermal window of A. ursinum (from -6.7 to 47.7°C; 54.5 K) and of Musa sp. (from -2.2°C to 49.5°C; 51.7 K) maximal quantum yield of PSII photochemistry (Fv/Fm) was fairly unaffected by temperature over more than 40 K. At low temperature Fv/Fm started to drop with ice nucleation but significantly only with initial frost injuries (temperature at 10% frost damage; LT10). The critical high temperature threshold for PSII (Tc) was 43.8°C in A. ursinum and 44.7°C in Musa sp. Under strong irradiation, exposure to temperatures exceeding the growth ones but being still nonlethal caused photoinhibition in both species. Severity of photoinhibition increased with increasing distance to the growth temperature range. ΔF/Fm′ revealed distinctly different optimum temperature ranges: 27-36°C for Musa sp. and 18-27°C for A. ursinum exceeding maximum growth temperature by 2-7 K. In both species only at temperatures > 30°C zeaxanthin increased and violaxanthin decreased significantly. At nonlethal low temperature relative amounts of xanthophylls remained unchanged. At temperatures > 40°C β-carotene increased significantly in both species. In Musa sp. lutein and neoxanthin were significantly increased at 45°C, in A. ursinum lutein remained unchanged, neoxanthin levels decreased in the supraoptimal temperature range. In darkness, Fv/Fm was highly temperature-insensitive in both species., a2_Under strong irradiation, whenever growth temperature was exceeded, photoinhibition occurred with xanthophylls being changed only under supraoptimal temperature conditions as an antiradical defence mechanism., A. Dongsansuk, C. Lütz, and G. Neuner., and Obsahuje bibliografii
To understand the interactive effects of O3 and CO2 on rice leaves; gas exchange, chlorophyll (Chl) fluorescence, ascorbic acid and glutathione were examined under acute (5 h), combined exposures of O3 (0, 0.1, or 0.3 cm3 m-3, expressed as O0, O0.1, or O0.3, respectively), and CO2 (400 or 800 cm3 m-3, expressed as C400 or C800, respectively) in natural-light gas-exposure chambers. The net photosynthetic rate (PN), maximum (Fv/Fm) and operating (Fq'/Fm') quantum efficiencies of photosystem II (PSII) in young (8th) leaves decreased during O3 exposure. However, these were ameliorated by C800 and fully recovered within 3 d in clean air (O0 + C400) except for the O0.3 + C400 plants. The maximum PSII efficiency at 1,500 μmol m-2 s-1 PPFD (Fv'/Fm') for the O0.3 + C400 plants decreased for all measurement times, likely because leaves with severely inhibited PN also had a severely damaged PSII. The
PN of the flag (16th) leaves at heading decreased under O3 exposure, but the decline was smaller and the recovery was faster than that of the 8th leaves. The Fq'/Fm' of the flag leaves in the O0.3 + C400 and O0.3 + C800 plants decreased just after gas exposure, but the Fv/Fm was not affected. These effects indicate that elevated CO2 interactively ameliorated the inhibition of photosynthesis induced by O3 exposure. However, changes in antioxidant levels did not explain the above interaction. and H. Kobayakawa, K. Imai.
Soil salinization and alkalinization frequently co-occur in naturally saline and alkaline soils. To understand the characteristics of mixed salt-alkali stress and adaptive response of Medicago ruthenica seedlings to salt-alkali stress, water content of shoots, growth and photosynthetic characteristics of seedlings under 30 salt-alkaline combinations (salinity 24-120 mM and pH 7.03-10.32) with mixed salts (NaCl, Na2SO4, NaHCO3, and Na2CO3) were examined. The indices were significantly affected by both salinity and pH. The interactive effects between salt and alkali stresses were significant, except for photosynthetic pigments. Water content of shoots, relative growth rates of shoots and roots and pigment concentrations showed decreasing trends with increasing salinity and alkalinity. The root activity under high alkalinity and salinity treatments gradually decreased, but was stimulated by the combined effects of low alkalinity and salinity. The survival rate decreased with increased salinity, except at pH 7.03-7.26 when all plants survived. Net photosynthetic rate, stomatal conductance and intercellular CO2 concentration decreased with increased salinity and pH. M. ruthenica tolerated the stress of high salt concentration when alkali concentration was low, and the synergistic effects of high alkali and high salt concentrations lead to the death of some or all seedlings. M. ruthenica appeared to be salt-alkali tolerant. Reducing the salt concentration or pH based on the salt components in the soil may be helpful to abate damage from mixed salt-alkaline stress. and J. Y. Yang ... [et al.].
Chlorophyll (Chl) content, dry mass, relative water content (RWC), leaf mass per area (LMA), proline (Pro) content, malondialdehyde (MDA) content, superoxide dismutase (SOD) and peroxidase (POD) activity, PN-PAR response curves and gas exchange were studied to determine the effects of water stress on photosynthetic activity, dry mass partitioning and metabolic changes in four provenances of neem (Azadirachta indica A. Juss). The results indicated that provenance differences existed in the adaptation response to water stress that included changes to growth strategies coupled with ecophysiological and metabolic adjustments. As water stress increased, stomatal conductance (gs), net photosynthetic rate (PN), transpiration rate (E), and leaf RWC decreased while LMA increased in all provenances. Dry mass was reduced in droughted plants and the percentage increased in dry mass allocated to roots, and enzyme activities of SOD and POD were highest in neem originating from Kalyani (KA) provenance and lowest in neem originating from New Dehli (ND) provenance. In contrast, water stress increased MDA content least in KA and most in ND. Furthermore, neem originating from ND also had the greatest decrease in Chl a/b ratio while the ratio was least affected in neem originating from KA. These findings suggest neem originating from KA may have more drought resistance than neem originating from ND. The data from PN-PAR response curves are less clear. While these curves showed that drought stress increased compensation irradiance (Ic) and dark respiration (RD) and decreased saturation irradiance (Is) and maximum net photosynthetic rate (Pmax), the extent of decline in P max was provenance dependent. P max under non-waterlimiting conditions was higher in neem originating from Jodhpur (MA) (about 14 μmol m-2 s-1) than in the other three provenances (all about 10 μmol m-2 s-1), but mild water stress had minimal effect on Pmax of these three provenances whereas Pmax of MA provenance declined to 10 μmol m-2 s-1, i.e. a similar value. However, under severe water stress P max of MA and KA provenances had declined to 40% of non-stressed values (about 6 and 4 μmol m-2 s-1, respectively) whereas the decline in Pmax of neem originating from Kulapachta (KU) and ND provenances was about 50% of nonstressed values (about 5 μmol m-2 s-1). These data suggest the PN responses of KU and ND provenances are most tolerant, and KA and MA least tolerant to increasing water stress, but also suggest MA provenance could be the most desired under both non-water-limiting and water-limiting conditions due to highest Pmax in all conditions. and Y. X. Zheng ... [et al.].
We studied how tomato (Lycopersicon esculentum Mill.) chloroplast omega-3 fatty acid desaturase gene (Lefad7) overexpression enhanced low-temperature (LT) tolerance in transgenic tomato plants. In these plants, the content of linolenic acid (18:3) markedly increased and, correspondingly, the content of linoleic acid (18:2) decreased. Similar changes were found after 6 h under LT (4°C) treatment. Under LT stress, wild type (WT) tomato plants showed a much greater increase in relative electrolyte leakage and malondialdehyde (MDA) contents compared with transgenic plants. Transgenic plants exhibited higher activities of antioxidative enzymes and a lower content of reactive oxygen species (ROS). Transgenic plants maintained a relatively higher level of the net photosynthetic rate (PN) and chlorophyll (Chl) content than WT plants under LT stress. Taken together, we suggested that overexpression of Lefad7 enhanced LT tolerance by changing the composition of membrane lipids in tomato plants, with the increased content of trienoic fatty acids and reduced content of dienoic fatty acids that led to series of physiological alterations., X. Y. Liu ... [et al.]., and Obsahuje bibliografii
Industrial chicory, Cichorium intybus L., has rather poor early vigour under the typical early spring morning conditions of low temperatures and high light intensity. Screening tools are being developed to assess the cold tolerance/sensitivity of young industrial chicory plants under these conditions. Refinement of such tools requires better understanding of the plants' physiological responses. In this paper we discuss the effects of growth temperature (GT), measurement temperature (MT), and measuring light intensity (ML) on the relaxation of the Kautsky curve. We chose the chicory variety 'Hera', as it is known to possess a good average early vigour. Young plants of the variety 'Hera' were grown at three temperatures (GT): 16°C (reference), 8°C (intermediate), and 4°C (cold stress). The dark relaxation kinetics were analyzed at different light intensities (ML) in combination with different measurement temperatures (MT). The three components of the nonphotochemical quenching process (NPQE, NPQT, and NPQI) were determined. NPQE was not affected by GT but was significantly affected by MT and ML. NPQT and NPQI were affected by all factors and their interactions. An acclimation effect for plants grown at low GT was detected. Acclimation resulted in lower NPQT and NPQI values. The halftime of the inhibition depending on NPQ (NPQI) was not affected by any of the factors investigated. Based on the data generated, we conclude that NPQI is a valuable parameter for screening the cold sensitivity of young industrial chicory plants. and P. Lootens ... [et al.].
Industrial chicory, Cichorium intybus L., is cultivated for the production of inulin. Most varieties of industrial chicory exhibit rather poor early growth, which limits further yield improvements in their European cultivation area. The poor early growth could be due to suboptimum adaptation of the gene pool to growth at low temperatures, sometimes in combination with high light intensities, which is typical of early-spring mornings. We have used chlorophyll (Chl) a fluorescence to evaluate the response of young plants of the cultivar 'Hera' to low temperatures and high light intensities. Plants were grown at three temperatures: 16°C (reference), 8°C (intermediate), and 4°C (cold stress). Light-response measurements were carried out at different light intensities in combination with different measurement temperatures. Parameters that quantify the photosystem II (PSII) operating efficiency (including PSII maximum efficiency and PSII efficiency factor) and nonphotochemical quenching (NPQ) are important to evaluate the stress in terms of severity, the photosynthetics processes affected, and acclimation to lower growth temperatures. The results clearly demonstrate that in young industrial chicory plants the photosynthetic system adapts to lower growth temperatures. However, to fully understand the plant response to the stresses studied and to evaluate the long-term effect of the stress applied on the growth dynamics, the subsequent dark relaxation dynamics should also be investigated. and S. Devacht ... [et al.].