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.