Drought significantly constrains higher yield of alfalfa (Medicago sativa L.) in arid and semiarid areas all over the world. This study evaluated the responses of leaf cuticular wax constituents to drought treatment and their relations to gas-exchange indexes across six alfalfa cultivars widely grown in China. Water deficit was imposed by withholding water for 12 d during branching stage. Cuticular waxes on alfalfa leaves were dominated by primary alcohols (41.7-54.2%), alkanes (13.2-26.9%) and terpenes (17.5-28.9%), with small amount of aldehydes (1.4-3.4%) and unknown constituents (4.5-18.4%). Compared to total wax contents, the wax constituents were more sensitive to drought treatment. Drought decreased the contents of primary alcohol and increased alkanes in all cultivars. Alkane homologs, C25, C27, and C29, were all negatively correlated with photosynthetic rate, transpiration rate, stomatal conductance, and leaf water potential. Under drought conditions, both stomatal and nonstomatal factors were involved in controlling water loss from alfalfa leaves. No direct relationship was observed between wax contents and drought resistance among alfalfa cultivars. An increase in alkane content might be more important in improving drought tolerance of alfalfa under water deficit, which might be used as an index for selecting and breeding drought resistant cultivars of alfalfa., Y. Ni ... [et al.]., and Obsahuje bibliografii
Five decades ago, a novel mode of CO2 assimilation that was later described as C4-photosynthesis was discovered on mature leaves of maize (Zea mays L.) plants. Here we show that 3- to 5-day-old developing maize leaves recapitulate the evolutionary advance from the ancient, inefficient C3 mode of photosynthesis to the C4 pathway, a mechanism for overcoming the wasteful process of photorespiration. Chlorophyll fluorescence measurements documented that photorespiration was high in 3-day-old juvenile primary leaves with non-specialized C3-like leaf anatomy and low in 5-day-old organs with the typical "Kranz-anatomy" of C4 leaves. Photosynthetic gas (CO2)-exchange measurements on 5-day-old leaves revealed the characteristic features of C4 photosynthesis, with a CO2 compensation point close to zero and little inhibition of photosynthesis by the normal oxygen concentration in the air. This indicates a very low photorespiratory activity in contrast to control experiments conducted with mature C3 sunflower (Helianthus annuus L.) leaves, which display a high rate of photorespiration. and U. Kutschera ... [et al.].
The effects of water stress on leaf surface morphology (stomatal density, size, and trichome density of both adaxial and abaxial surfaces) and leaf ultrastructure (chloroplasts, mitochondria, and cell nuclei) of eggplant (Solanum melongena L.) were investigated in this study. Higher stomata and trichome densities were observed on abaxial surface compared with the adaxial surface. Compared with well watered (WW) plants, the stomata and trichome density of the abaxial surface increased by 20.39% and 26.23% under water-stress condition, respectively. The number of chloroplasts per cell profile was lesser, the chloroplasts became round in a shape with more damaged structure of membranes, the number of osmiophilic granules increased, and the number of starch grains decreased. The cristae in mitochondria were disintegrated. The cell nuclei were smaller and the agglomerated nucleoli were bigger than those of WW plants. Our results indicated that the morphological and anatomical responses enhanced the capability of plants to survive and grow during stress periods., Q. S. Fu ... [et al.]., and Obsahuje bibliografii
Nondestructive methods to estimate individual leaf area (LA) accurately, by leaf length (L) and/or width (W), is helpful for the in situ and successive LA measurements. However, leaf shape and size may covary with environment and thus alter the coefficients of LA estimation models. To test such hypothesis, we carried out an experiment by measuring Saussurea stoliczkai C. B. Clarke leaves along an altitudinal transect in Damxung county, central Tibet. In July 2011, we selected seven sites at about every 150 m in altitude from 4,350 m to 5,250 m a.s.l. A total of 1,389 leaves (182 to 203 leaves for each site) were measured. For each site, models developed by two leaf dimensions [LA = a (L×W) + b] could estimate LA more accurately than those by single dimension. L, W, LA and leaf shape index (L:W ratio) all decreased with increasing altitude, leading to significant differences in coefficients of two-dimension model between almost every two sites. Accordingly, a common
two-dimension model is unlikely to occur for S. stoliczkai across the whole altitudinal transect, indicating that the varying leaf shape may alter the coefficient of LA estimation models., Z. Wang, L. Zhang., and Obsahuje bibliografii
The ability of plants to increase their net CO2 assimilation rate in response to increased irradiance is due to morphological and physiological changes, which might be related to their shade tolerance and leaf ontogeny, but few studies have considered morphology and physiology. Two sympatric oak species (the shade-tolerant Q. petraea and the comparatively shade-intolerant Q. pyrenaica) were grown in hydroponic solution in low-light (LL) and high-light (HL) conditions. 5 months after leaf expansion under these conditions, half of the LL plants were transferred to high light (TLH). Transfer of Q. pyrenaica, from low- to high light led to photoinhibition and after 21 days in higher light there was little acclimation of the maximum rate of carboxylation (VCmax) or the maximum rate of electron transport (Jmax). Q. pyrenaica TLH plants showed lower stomatal conductance at all times compared to plants growing in LL. Stomatal closure was the main limitation to photosynthesis after transfer in Q. pyrenaica. The increase in evaporative demand upon TLH did not affect hydraulic conductivity of Q. pyrenaica. In contrast, the more shade-tolerant Q. petraea showed a greater degree of acclimation of gas exchange in TLH than Q. pyrenaica and two weeks after transfer gas-exchange rates were as high as in LL plants. In Q. petraea, the most important changes occurred at the level of leaf biochemistry with significant increase in VCmax that decreased the Jmax/VCmax ratio below values recorded in HL plants. However, this potential increase in photosynthesis was at least partially hamstrung by a decrease in internal conductance, which highlights the importance of internal conductance in acclimation to higher light in mature leaves. Neither oak species reached the photosynthetic rates of HL plants; however a trend towards leaf acclimation was observed in Q. petraea while the transfer was harmful to the leaves of Q. pyrenaica developed in the shade. and F. J. Cano ... [et al.].
The impact of a heterogeneous distribution of actinic light within a leaf chamber for photosynthetic measurements by gas exchange on the photosynthesis-irradiance relationship was investigated. High-resolution light distributions were measured over the area of a commercially available clamp-on leaf chamber equipped with build-in red and blue LEDs, as well as over the area of a custom-made leaf chamber with external light source, using a low-cost digital camera and freely available software. The impact of the measured heterogeneity on the photosynthesis-irradiance response curve was calculated for two realistic scenarios. When the average light intensity over the leaf chamber area was estimated accurately, heterogeneity had minor effects on the photosynthesis-irradiance response curve. However, when the irradiance was measured in the chamber centre, which is common practice, and assumed to be homogeneous, for both leaf chambers the photosynthesis-irradiance response curve was subject to considerable error and led to serious underestimation of the light-limited quantum yield of photosynthesis. Additionally, mixed light sources with different heterogeneity patterns per light source, such as in the clamp-on leaf chamber, potentially increase errors due to heterogeneous physiological responses to light spectrum. High-resolution quantification of the leaf-chamber light distribution enables calculation of the correct average light intensity and already resolves the most pressing problems associated with heterogeneity. To exclude any light-distribution related errors in
gas-exchange measurements a leaf chamber and actinic irradiance source design with a homogeneous light distribution is an absolute requirement. and S. W. Hogewoning ...[et al.].
In the present studies, we have found a fragment of amino acid sequence, called TFT motif, both in light-dependent protochlorophyllide oxidoreductase (LPOR) and in the L subunit of dark-operative (light-independent) protochlorophyllide oxidoreductases (DPOR). Amino acid residues of this motif shared similar physicochemical properties in both types of the enzymes. In the present paper, physicochemical properties of amino acid residues of this common motif, its spatial arrangement and a possible physiological role are being discussed. This is the first report when similarity between LPOR and DPOR, phylogenetically unrelated, but functionally redundant enzymes, is described., M. Gabruk ... [et al.]., and Obsahuje bibliografii
Dark-grown seedlings of Pinus mugo Turra and Pinus sylvestris L. accumulate chlorophyll (Chl) and its precursor protochlorophyllide (Pchlide). Pchlide reduction is a key regulatory step in Chl biosynthesis. In the dark, Pchlide is reduced by light-independent Pchlide oxidoreductase (DPOR) encoded by three plastid genes chlL, chlN, and chlB (chlLNB). To investigate the differences in chlLNB gene expressions, we compared the dark-grown and 24-h illuminated seedlings of P. mugo and P. sylvestris. Expression of these genes was found constitutive in all analyzed samples. We report light-independent accumulation of important proteins involved in Chl biosynthesis (glutamyl-tRNA reductase) and photosystem formation (D1 and LHCI). Chl and Pchlide content and plastid ultrastructure studies were also performed. and K. Breznenová ... [et al.]
In this article, the effects of drought stress (DS) on gas exchange, chlorophyll (Chl) a fluorescence and Calvin cycle enzymes in Phaseolus vulgaris are evaluated. Three-week-old plants were exposed to DS by receiving only so much water every evening to ensure 30% field capacity water content overnight. After three days under these conditions, we observed that DS induced a decline of the CO2 assimilation. Gas-exchange data showed that the closure of stomata during DS did not lead to a concomitant decline in calculated intercellular CO2 concentration. Moreover, DS plants showed a reduction of the photochemical Chl fluorescence quenching, photosystem II quantum yield and electron transport rate and a higher pH gradient and more heat dissipation as compared to controls. The activity of Calvin cycle enzymes, Rubisco, sFBPase, and Ru5PK, decreased strongly in DS plants as compared to controls. Data analysis suggest that the decrease of CO2 assimilation under drought conditions is not related to a diminished capacity of the use of NADPH and ATP but probably to the decline of enzyme activity involved in RuBP regeneration (Ru5PK). and M. C. Dias, W. Brüggemann.
The aim of this study was to evaluate the effects of low air temperature during nocturnal (TN) and diurnal (TD) periods as well as the substrate temperature (TS) on photosynthesis of 'Valencia' orange tree grafted on Rangpur lime rootstock. The experiment was carried out in a growth chamber with seven-month-old plants. The plants were exposed to the following temperature regimes: low substrate temperature (LTS, with: TD = 28°C, TN = 20°C,
TS = 10°C); low air temperature during night (LTN, with: TD = 28°C, TN = 10°C, TS = 26°C); low temperature during nighttime and also low substrate temperature (LTSN, with: TD = 28°C, TN = 10°C,
TS = 10°C); low air temperature during both diurnal and nocturnal periods (LTND, with: TD = 17°C, TN = 10°C, TS = 26°C); and finally to low air temperature (night and day) and low substrate temperature (LTSND, with: TD = 17°C, TN = 10°C, TS = 10°C). As reference (control), plants were subjected to TD = 28°C, TN = 20°C, and TS = 26°C. Measurements of leaf gas exchange, photochemical activity and carbohydrate concentrations were performed after six days of exposure to each thermal treatment. Compared to the control, all thermal regimes caused reductions in photosynthesis due to diffusive and metabolic limitations. The photoinhibition was transient in plants exposed to night and substrate low temperatures, whereas it was severe and chronic in plants subjected to chilling during the diurnal period. However, the lowest photosynthesis was observed in plants with low substrate temperature of 10°C (in LTS, LTSND and LTSN treatments), regardless of air temperature. The occurrence of cold night and/or its combination with low substrate temperature caused accumulation of starch in leaves. When considering carbohydrate concentrations in stems and roots, it was not possible to establish a clear response pattern to chilling. In conclusion, the low substrate temperature causes a greater reduction of CO2 assimilation in citrus plants as compared to the occurrence of low air temperature, being such response a consequence of diffusive and biochemical limitations. and C. M. A. Santos ... [et al.].