Photosystem II (PSII) photochemistry was examined by chlorophyll (Chl) a fluorescence analysis in high-yield rice LYPJ flag leaves during senescence. Parameters deduced from the JIP-test showed that inhibition of the donor side of PSII was greater than that of the acceptor side in hybrid rice LYPJ. The natural senescence process was accompanied by the increased inactivation of oxygen-evolving complex (OEC) and a lower total number of active reaction centers per absorption. It indicated that the inhibition of electron transport caused by natural senescence might be caused partly by uncoupling of the OEC and/or inactivation of PSII reaction centers. Chl fluorescence parameters analyzed in this study suggested that energy dissipation was enhanced in order to protect senescent leaves from photodamage. Nevertheless, considerably reduced PSI electron transport activity was observed at the later senescence. Thus, natural senescence inhibited OEC-PSII electron transport, but also significantly limited the PSII-PSI electron flow., Y. W. Wang, C. Xu, C. F. Lv, M. Wu, X. J. Cai, Z. T. Liu, X. M. Song, G. X. Chen, C. G. Lv., and Seznam literaruty
Under optimal conditions, most of the light energy is used to drive electron transport. However, when the light energy exceeds the capacity of photosynthesis, the overall photosynthetic efficiency drops down. The present study investigated the effects of high light on rice photooxidation-prone mutant 812HS, characterized by a mutation of leaf photooxidation 1 gene, and its wild type 812S under field conditions. Our results showed no significant difference between 812HS and 812S before exposure to high sunlight. However, during exposure to high light, shoot tips of 812HS turned yellow and their chlorophyll (Chl) content decreased. Transmission electron microscopy showed that photooxidation resulted in significant damage of chloroplast ultrastructure. It was confirmed also by inhibited photophosphorylation and reduced ATP content. The decreased coupling factor of ATP, Ca2+-ATPase and Mg2+-ATPase activities also verified these results. Further, significantly enhanced activities of antioxidative enzymes were observed during photooxidation. Malondialdehyde, hydrogen peroxide, and the superoxide generation rates also increased. Chl a fluorescence analysis found that the performance index and maximum quantum yield of PSII declined on August 4, 20 days after high-light treatment. Net photosynthetic rate also decreased and substomatal CO2 concentration increased in 812HS at the same time. In conclusion, our findings indicated that excessive energy triggered the production of toxic reactive oxygen species and promoted lipid peroxidation in 812HS plants, causing severe damage to cell membranes, degradation of photosynthetic pigments and proteins, and ultimately inhibition of photosynthesis., J. Ma, C. F. Lv, B. B. Zhang, F. Wang, W. J. Shen, G. X. Chen, Z. P. Gao, C. G. Lv., and Obsahuje seznam literatury
Drought impacts severely crop photosynthesis and productivity. Development of transgenic rice overexpressing maize phosphoenolpyruvate carboxylase (PEPC) is a promising strategy for improving crop production under drought stress. However, the molecular mechanisms of protection from PEPC are not yet clear. The objective of this study was: first, to characterize the response of individual photosynthetic components to drought stress; second, to study the physiological and molecular mechanisms underlying the drought tolerance of transgenic rice (cv. Kitaake) over-expressing maize PEPC. Our results showed that PEPC overexpressing improved the ability of transgenic rice to conserve water and pigments during drying as compared to wild type. Despite the fact that drought induced reactive oxygen species and damaged photosystems (especially, PSI) in both lines, higher intercellular CO2 concentration protected the photosynthetic complexes, peptides, and also ultrastructure of thylakoid membranes against the oxidative damage in transgenic rice. In conclusion, although photosynthetic apparatus suffered an inevitable and asymmetric impairment during drought conditions, PEPC effectively alleviated the oxidative damage on photosystems and enhanced the drought tolerance by increasing intercellular CO2 concentration. Our investigation provided critical clues for exploring the feasibility of using C4 photosynthesis to increase the yield of rice under the aggravated global warming., W. J. Shen, G. X. Chen, J. G. Xu, Y. Jiang, L. Liu, Z. P. Gao, J. Ma, X. Chen, T. H. Chen, and C. F. Lv., and Obsahuje seznam literatury