Photosynthesis has walked into the path of evolution for over millions of years. Organisms relying directly on photosynthesis, when subjected to adverse environments for a long duration, experience retardation in their growth and development. Salinity stress is perceived as one of the major threats to agriculture as it can cause an irreversible damage to the photosynthetic apparatus at any developmental stage of the plant. However, halophytes, a special category of plants, carry out all life processes, including photosynthesis, without showing any compromise even under high saline environments. The fascinating mechanism for Na+ exclusion from cytosol besides retaining photosynthetic efficiency in halophytes can provide a valuable genetic resource for improving salt stress tolerance in glycophytes. Understanding how plants stabilize their photosynthetic machinery and maintain the carbon balance under saline conditions can be extremely useful in designing crops for saline and dry lands., S. Wungrampha, R. Joshi, S. L. Singla-Pareek, A. Pareek., and Obsahuje bibliografické odkazy
The microstructure of leaves and ultrastructure of chloroplasts were examined in tomato (Lycopersicon esculentum L.) plants treated with elevated temperature. Plants were exposed to 35°C for 30 d after florescence. The plants grown continuously under 25°C served as controls. Compared with the controls, the net photosynthetic rate (PN) in stressed plants decreased significantly. Stomatal conductance, intercellular CO2 concentrations, the rate of transpiration, and the limitation of stomatal conductance showed that the decrease in PN was caused mainly by nonstomatal restrictions. Meanwhile, stomata density increased significantly in the stressed plants. The stomata status of opening and closing became disorganized with a prolonged 35°C exposure. The damage of chloroplast membrane occurred earlier and was more serious in the plants under elevated temperature. At the same time, the thylakoids were loosely distributed with lesser grana, but the number of lipid droplets increased in chloroplasts. The number of starch grains in chloroplasts increased first and then decreased. In addition, the length of the main nerve in leaves increased and the main vein showed distortion in the plants stressed by 35°C. An increase was observed in the number of cells on the abaxial side of the main vein and these cells were overly congregated. The thickness of a vertical section became thinner in the stressed leaves. The cells of the upper epidermis thinned, and the ratio of palisade tissue to spongy tissue decreased. Generally, the photosynthetic apparatus of tomato changed significantly and the changed chloroplast ultrastructure might be one of the important reasons that caused the decrease of PN under 35°C., J. Zhang, X. D. Jiang, T. L. Li, X. J. Cao., and Obsahuje bibliografii
To evaluate utility of different salt-tolerant lines, three soybean lines with different resistance to salt were planted in the field under control and salt-stress conditions for two years. The results showed that net photosynthetic rate (PN) was significantly different among lines at the anthesis stage and decreased on average by 13.6-34.1% under conditions of salt stress. The stomatal conductance was a primary limiting factor for the reduction of PN under salt stress. Meanwhile, the grain yield (GY) decreased on average by 14.0-35.3% among lines under salt stress. The salt-tolerant lines S111-9 and S113-6 showed higher PN and GY under salt stress in comparison with the salt-sensitive cultivar Melrose. Regression analysis indicated that there was extremely significantly positive correlation between GY and PN under field conditions. Therefore, PN might be used as a physiological index for field resistance of soybean to salt stress., Y. He, Y. Chen, C. L. Yu, K. X. Lu, Q. S. Jiang, J. L. Fu, G. M. Wang, D. A. Jiang., and Obsahuje bibliografii
This study compared the relationship between chlorophyll (Chl) content, gas exchange, Chl fluorescence characteristics, and leaf color, using paired near-isogenic lines (NILs) of a medium-green leaf inbred line SN12 and a yellow-green leaf mutant SN62 to explore the photosynthesis of the yellow-green mutant. The SN62 was found in a female parent, Xianyu 335, which grew normally, although there were small yellow spots on the leaves at the seedling stage and yellow-green leaves appeared from the seedling to the maturation stage. The results indicated that Chl a (b), quantum efficiency of PSII, and maximal quantum yield of PSII photochemistry of SN62 were significantly lower than those of SN12, but there were almost no differences in the net photosynthetic rate (P N). There was no significant correlation between Chl a (b) and P N of inbred lines with different leaf colors. In the reproductive stage, photochemical quenching, effective quantum yield of PSII photochemistry, and the electron transport rate of SN62 increased obviously, and all parameter values exceeded the values of SN12. It explained that increasing the openness of the PSII reaction center was able to compensate for the lower Chl content, which was beneficial for harvesting more light energy for photochemical reactions. It also ensured that P N was not reduced., X. M. Zhong, S. F. Sun, F. H. Li, J. Wang, Z. S. Shi., and Obsahuje seznam literatury
Physiological responses from sensitive (S156) and resistant (R123) genotypes of ozone bioindicator, snap bean, were investigated after exposing the plants to cumulative, phytotoxic ozone amounts. Daily course of gas-exchange parameters showed delayed stomatal response in S156 leaves to environmental changes comparing to the response of R123 leaves. Potential photosynthetic quantum conversion, Stern-Volmer nonphotochemical quenching (NPQ), and maximum photochemical efficiency of PSII (Fv/Fm) values changed differently in the two genotypes between the first and last measuring days. We concluded that the higher ozone sensitivity originated at least partly from inferior regenerating and/or antioxidant capacity. Experimental protocol proved to be determinant on chlorophyll fluorescence parameters: Fv/Fm and NPQ declined at midday, and only the sensitive leaves showed a slight increase in NPQ between 12 h and 16 h. We explained these results by moderately high temperatures and shade-adapted state of our experimental plants under substantial ozone stress. On the base of temperature dependence of minimal fluorescence yield (F0), critical temperature proved to be higher than 32.7°C for Phaseolus vulgaris under these conditions. We found a strong linear correlation between NPQ and nonphotochemical quenching of F0, indicating that NPQ was determined mostly by energy-dependent quenching (qE). The qE is the light-harvesting complex located component of NPQ and depends on the amount of zeaxanthin molecules bound in PSII proteins. Thus, difference between daily courses of NPQ in the two genotypes was probably due to different ways of utilization of the zeaxanthin pool under the interactive effect of ozone and moderate heat stress., V. Villányi, Z. Ürmös, B. Turk, F. Batič, Z. Csintalan., and Obsahuje bibliografii
While photosynthesis of soybean has been enhanced by breeding, it remains to be clarified whether the improvement of root function could bring a further increase of photosynthetic capacity for the development of soybean cultivars. The objective of this grafting experiment was to determine the influence of record-yield soybean cultivars, Liaodou14 (L14) and Zhonghuang35 (Z35), as rootstocks on photosynthetic traits of cultivars released in different decades. Grafting of various soybean cultivars onto L14 or Z35 rootstocks showed a higher root physiological activity, which resulted in significant increases in some photosynthetic traits at the late grain-filling stage compared with the non-grafted and self-grafted plants. The genetic gain for some photosynthetic traits of cultivars released from 1966 to 2006 increased by using L14 and Z35 as rootstocks. It suggested that the photosynthetic traits of the recently released cultivars could increase more if their root functions are improved., S. Y. Li, F. Teng, D. M. Rao, H. J. Zhang, H. Y. Wang, X. D. Yao, C. M. Yu, C. H. Li, M. Z. Zhao, S. K. St. Martin, F. T. Xie., and Obsahuje seznam literatury
Predicting the effects of increased ultraviolet-B (UV-B) radiation due to stratospheric ozone depletion on temperate desert ecosystems requires better knowledge of the ecophysiological response of common moss species. The aim of the current work was to determine whether elevated UV-B radiation affected photosynthetic performance and chloroplast ultrastructure of two moss crusts and whether response differences were observed between the crusts. In laboratory experiments, Bryum argenteum and Didymodon vinealis, which show microdistributions and are dominant in soil crusts at the Tengger Desert, Northern China, were subjected to four levels of UV-B radiation of 2.75 (control), 3.08, 3.25, and 3.41 W m-2 for 10 days, simulating 0, 6, 9, and 12% of stratospheric ozone at the latitude of Shapotou, respectively. The results showed that chlorophyll a fluorescence parameters (i.e., the maximal quantum yield of PSII photochemistry, the effective quantum yield of PSII photochemistry, and photochemical quenching coefficient), pigment contents, soluble protein contents, and the ultrastructure were negatively influenced by elevated UV-B radiation and the degree of detrimental effects significantly increased with the intensity of UV-B radiation. Moreover, results indicated that B. argenteum was probably more sensitive to supplementary UV-B radiation than D. vinealis. Therefore, we propose the use of B. argenteum crusts as a bioindicator of responses to elevated UV-B radiation., R. Hui, X. R. Li, R. L. Jia, L. C. Liu, R. M. Zhao, X. Zhao, Y. P. Wei., and Obsahuje bibliografii
Monitoring some parameters would help to overcome the difficulties that can affect in vitro-grown plants during the crucial step of their acclimatization. Thus, after the determination of net photosynthesis and other parameters during acclimatization of in vitro-grown olive plantlets, we concluded that three months after the transfer to ex vitro, the in vitro-grown olive plants become well acclimated. In fact, even though the net photosynthesis, relatively high in vitro, recorded low values after 15 d from the transfer, it reverted back to its standard rates after 180 d of acclimatization. Transpiration and stomatal conductance first increased significantly with a maximum of 6.22 mmol(H2O) m-2 s-1 and 1.8 mmol(H2O) m-2 s-1, respectively, but they regressed to very low values after 180 d of acclimatization. Some changes in the leaf anatomy were also observed; the reduction of stomata density and inversely, the increase of trichome density, especially on the abaxial side of the leaves, were observed., A. Chaari-Rkhis, M. Maalej, A. Chelli-Chaabouni, L. Fki, N. Drira., and Obsahuje seznam literatury
Glyphosate herbicide caused oxidative stress and exhibited negative effects on photosynthesis and gas exchange of peanut [Arachis hypogaea L. cv. Giza (G) 5 and 6] leaves. We demonstrated that glyphosate caused various morphological symptoms, such as chlorosis, yellowing, and appearance of curly edges in leaves treated with high doses of herbicide in both cultivars; however, the G5 cultivar was more sensitive and showed severer symptoms. Glyphosate lowered photosynthesis and reduced contents of pigments and proteins as well as free amino acids in both cultivars. The gas-exchange parameters, such as photosynthetic (P N) and transpiration rate (E), were highly altered by the glyphosate application. For example, P N and E were reduced by 65 and 61%, respectively, in G5 treated with high dose of glyphosate compared with control. Antioxidant enzymes, such as peroxidase, catalase, ascorbate peroxidase, and superoxide dismutase were induced by both low and high concentrations in the glyphosate-treated leaves. Moreover, the level of lipid peroxidation, indicated by a malondialdehyde content, as well as the hydrogen peroxide content increased in the glyphosate-treated leaves. However, an increase in total antioxidant activity was detected in leaves and this reflected changes in the antioxidant status and accumulation of antioxidants as a defense mechanism against glyphosate toxicity in peanut., D. E. M. Radwan , K. A. Fayez., and Obsahuje seznam literatury
Alkalies are important agricultural contaminants complexly affecting plant metabolism. In this study, rice seedlings were subjected to alkaline stress (NaHCO3:Na2CO3 = 9:1; pH 8.9) for 30 days. The results showed that stress mightily reduced net photosynthetic rate (PN), but slightly decreased transpiration rate and stomatal conductance. This indicated that decline of PN might be a result of nonstomatal factors. Alkaline stress caused a large accumulation of Na+ in leaves up to toxic concentration, which possibly affected chloroplast ultrastructure and photosynthesis. We found that alkaline stress reduced chlorophyll fluorescence parameters, such as ratios of Fv′/Fm′, Fv/Fm, photosystem (PS) II efficiency, and electron transport rates in rice plants, i.e. it influenced the efficiencies of photon capture and electron transport by PSII. This might be a main reason for the decrease of PN under such conditions. Deficiency of minerals could be another reason for the decline of PN. Alkaline stress lowered contents of N, K, Cu, Zn, P, and Fe in rice plants. In addition, the stress strongly affected metabolism of amino acids. This might be caused by imbalance in carbon metabolism as a result of photosynthesis reduction., Z.-H. Wu, C.-W. Yang, M.-Y. Yang., and Obsahuje bibliografii