Water deficit is an important exogenous factor that enhances the influx of sucrose into sugarcane (Saccharum spp.) stem internodes during ripening, when photosynthetic ability in supplying sinks is essential. The aim of this study was to test the hypothesis that drought tolerance in sugarcane is associated with an effective antioxidant protection during the ripening phase that might maintain a favorable redox balance in chloroplasts and protect photosynthesis under drought conditions. Two commercial sugarcane varieties, IACSP94-2094 (tolerant) and IACSP96-2042 (sensitive), with contrasting behavior under water deficit, were subjected to water withholding during the ripening stage. Our results revealed that the tolerant variety was less affected by water deficit, maintaining photosynthesis for a longer period and showing a faster recovery after rehydration as compared to the sensitive one. As consequence, the tolerant variety faced lesser excess of light energy at PSII. The maintenance of photosynthesis under water deficit and its fast recovery after rehydration resulted in the lower leaf H2O2 concentration and favorable redox status in the drought-tolerant genotype, which was associated with stimulation of superoxide dismutase during ripening. Our results also revealed that ferric superoxide dismutase isoforms were strongly enhanced under drought conditions, playing an important role in chloroplast redox homeostasis., C. R. G. Sales, P. E. R. Marchiori, R. S. Machado, A. V. Fontenele, E. C. Machado, J. A. G. Silveira, R. V. Ribeiro., and Obsahuje seznam literatury
Insufficient attention has been paid to the physiological responses of sesame to drought and it is unclear if exogenous plant growth regulators are beneficial to drought-stressed sesame. Thus, a field study was conducted on seven Sesamum indicum genotypes affected by two levels of irrigation (60 and 80% depletions in available soil water) and by foliar-applied salicylic acid (SA; 0 and 0.6 mM). Water deficit led to depressions in net photosynthetic rate, stomatal conductance, leaf area index, chlorophyll a, b, and total chlorophyll contents, maximum quantum efficiency of PSII, and plant dry matter and seed yield, despite increases in carotenoid concentration, superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase activities. SA was found beneficial in ameliorating the depressions in all of the above characteristics, indicating that it could be applied for lessening the harmful effects of the drought stress., M. Yousefzadeh Najafabadi, P. Ehsanzadeh., and Obsahuje použitou literaturu
Syntrichia caninervis Mitt. is the dominant species in the moss crusts of the Gurbantunggut Desert, Northwestern China. We experimented with this species under controlled environmental conditions. Modulated chlorophyll (Chl) fluorescence was used to test the speed of recovery as evidenced by the time course of photosynthetic activity following remoistening. Transmission electron microscopy was used to explore the cytological characteristics of the leaf cells. Minimum and maximum fluorescence (F0 and FM) and photosynthetic yield (FV/FM) of photosystem II (PSII) recovered quickly when shoots were remoistened in the dark. This was especially the case of FV/FM; within the first minute of remoistening this reached 90% or more of the value attained after 30 min. These physiological changes were closely paralleled by cytological changes that indicated no damage to membranes or organelles. Correlation analysis showed that Chl fluorescence decreased both above and below a narrow moisture optimum. Our results underline the capability of S. caninervis to photosynthesize after remoistening. Utilizing precipitation events such as dew, fog, rain, and melting snow allows S. caninervis to survive and grow in a harsh desert environment. and J. Zhang ... [et al.].
Water and nitrogen (N) deficiency are two major constraints limiting the yield and quality of many oilseed crops worldwide. This study was designed to assess the response of Camelina sativa (L.) Crantz to the availability of N and water resources on photosynthesis and yield parameters. All the measured variables, which included plant height, root and shoot dry matter, root:shoot ratio, xylem pressure potential (XPP), yield components, photosynthetic parameters, and instantaneous water-use efficiency (WUE) were remarkably influenced by water and nitrogen supply. Net photosynthetic rate (PN) and yield components were significantly decreased more by water deficit than by N deficiency. XPP, stomatal conductance (gs), and intercellular CO2 concentration (C i) decreased substantially as the water deficit increased irrespective of the level of N application. WUE at the high N supply [100 and 150 kg(N) ha-1] dropped in a large degree as the increased water deficit due to a larger decrease in PN than transpiration rate (E). The results of this study suggest that the regulative capacity of N supply on photosynthetic and plant growth response is significantly affected by soil water status and C. sativa is more sensitive to water deficit than N supply. and X. Pan ... [et al.].
Cadmium inhibits photosynthetic capacity of plants by disturbing protein conformations, whereas phytocystatins prevent degradation of target proteins and are involved in abiotic stress tolerance. Two mustard (Brassica juncea L.) cultivars, Ro Agro 4001 and Amruta, were grown with Cd (50 µM) in order to study physiological and biochemical basis of differences in Cd tolerance. Amruta accumulated higher Cd and H2O2 concentrations in leaves than that of Ro Agro 4001. Cd significantly decreased photosynthesis and growth of plants in both cultivars by reducing a chlorophyll content, gas exchange parameters, and activity of Rubisco; the effects were more prominent in Amruta than those in Ro Agro 4001. The greater photosynthesis and growth of Ro Agro 4001 under Cd stress might be attributed to its higher phytocystatin activity together with greater ascorbate peroxidase activity, photosynthetic nitrogen-use efficiency, sulphur assimilation (ATP-sulphurylase activity and S content), and contents of cysteine and reduced glutathione compared to Amruta. In contrast, the activity of superoxide dismutase (SOD) was higher in Amruta than that of Ro Agro 4001 under control conditions, whereas the Cd treatment increased significantly the SOD activity in both cultivars with the greater increase in Ro Agro 4001. The fluorescence spectra of phytocystatin showed a lesser change in Ro Agro 4001 under Cd stress than that in Amruta suggesting higher resistance of Ro Agro 4001 to Cd. The higher phytocystatin activity under Cd stress in Ro Agro 4001 compared to Amruta enabled the plants to protect their proteins more efficiently. This resulted in a greater increase of photosynthetic capacity in Ro Agro 4001 than that of Amruta. Thus, the phytocystatin activity may be considered as a physiological parameter for augmenting photosynthesis and growth of mustard under Cd stress., T. S. Per, S. Khan, M. Asgher, B. Bano, N. A. Khan., and Obsahuje bibliografii
Plant traits of Malcolmia littorea growing at the Botanic Garden of Rome and transplanted from the wild population developing along the Latium coast (Italy) were analyzed. The highest photosynthetic rates [PN, 22.5 ± 0.5 μmol(CO2) m-2 s-1], associated to the highest chlorophyll content (Chl, 60 ± 5 SPAD units), and respiration rates [R, 11.1 ± 0.2 μmol(CO2) m-2 s-1] were reached in spring, when mean air temperature (Tm) was in the range 17°C to 23°C. PN, Chl, and R decreased by 86, 38, and 59% in summer when mean maximum air temperature (Tmax) was 30.3 ± 2.6°C. Leaf water potential decreased by 34% in summer compared to the spring value, and it was associated to a relative water content (RWC) of 74 ± 4%, and to a water-use efficiency (WUE) of 2.15 ± 0.81 μmol(CO2) mmol-1(H2O). Moreover, also low air temperatures determined a significant PN and R decreases (by 52 and 40% compared to the maximum, respectively). Responsiveness of gross photosynthetic rate (Pg) to R was higher than that to PN as underlined by the slope of the regression line between the two variables. The results underlined a low tolerance to both high- and low air temperatures of M. littorea. The selected key traits (R, WUE, Chl) by the discriminant analysis might be used to monitor the M. littorea wild population in the long time. The ex situ cultivated plants could be propagated and used to increase the individuals number of the wild population. and L. Gratani ... [et al.].
Photosynthetic pathways (e.g. C3, C4) and morphological functional types (e.g. trees, shrubs, high perennial grasses, perennial forbs) were identified for the native species from the Saskatchewan mixed prairie, using the data from references published between 1950 and 2003. Of the total 219 identified species in 145 genera and 45 families, 208 species in 137 genera and 44 families were found with C3 photosynthesis, and most of these species are dominants (e.g. Agropyron dasystachyum Hook. and Stipa spartea var. curtiseta Hitchc.). 11 species in 10 genera and 3 families were identified with C4 photosynthesis (e.g. Atriplex argentea Nutt., Andropogon scoparius Michx., Boutelou gracilis Lag., Calamovilfa longifolia Hook.). The amount of total identified C4 species in the region is much less than that from the South Dakota mixed prairie (27 species). Gramineae is the leading family with C4 photosynthesis (8 species), Chenopodiaceae ranks the second (2 species). Relatively less forb types [50 % perennial forbs (PEF) and 12 % annual forbs (ANF)] and more graminoid types (25 %) composition suggested that the rangelands in the region are relatively stable. Lacking of the knowledge on the optimal traits for PFTs classification in the region, further studies (e.g. C3 and C4 plant identification and optimal trait selection) are needed to explore the relationships between PFTs and vegetation variations, as well as land-use and climate changes. and R. Z. Wang, X. Q. Liu, Y. Bai.
Morphological functional types and photosynthetic pathway types were identified for the forage species from steppe communities in Inner Mongolia, China, using the data of both field survey and published papers. Seven typical steppe communities were selected to investigate the morphological functional type and photosynthetic pathway type compositions and plant functional type (PFT) diversity in steppe communities at regional scale. Morphological functional types, based on plant height and leaf type combined with life span, were optimal for comparing the community differences in the region, while photosynthetic pathway types were fairly coarse for such studies. Of the seven morphological functional types in the steppe communities, perennial forbs (PEF) were the dominant type, and 60 % of species belonged to this type. Each of the high perennial grass (HPG), short perennial grass (SPG), and annual grass (ANG) types represented less than 10 % of the total, even though the grass species were dominant in the seven steppe communities. The differences of PFTs between the steppe communities were remarkable, and the PFT richness and diversity increased from the communities with moist conditions to the ones with dry environments.
Two foxtail millet (Setaria italica L.) varieties were subjected to different shading intensity treatments during a grain-filling stage in a field experiment in order to clarify physiological mechanisms of low-light effects on the yield. Our results showed that the grain fresh mass per panicle, yield, photosynthetic pigment contents, net photosynthetic rate, stomatal conductance, effective quantum yield of PSII photochemistry, and electron transport rate decreased with the increase of shading intensity, whereas the intercellular CO2 concentration increased in both varieties. In addition, shading changed a double-peak diurnal variation of photosynthesis to a one-peak curve. In conclusion, the lower yield of foxtail millet was caused mainly by a reduction of grain mass assimilated, a decline in chlorophyll content, and the low photosynthetic rate due to low light during the grain-filling stage. Reduced light energy absorption and conversion, restricted electron transfer, and reduced stomatal conductance might cause the decrease in photosynthesis., X. Y. Yuan, L. G. Zhang, L. Huang, X. Qi, Y. Y. Wen, S. Q. Dong, X. E. Song, H. F. Wang, P. Y. Guo., and Obsahuje bibliografii
Depressions of the photosynthetic and respiration rates, found over a wide range of water stress, were remarkably reversible after resaturation of wheat leaf segments.