Photosynthetic Apparatus Response To Heat Stress And The Mechanisms In Two Different Cotton With Various Leaf Colours

As the basis of plant growth and development, photosynthesis provides matter and energy for plant growth and development. High temperature condition, however, severely restricts photosynthesis which then influences crops yield and quality. Therefore, the research on the mechanism of the influence of high temperature stress on photosynthesis is of great significance.In this study, the differences in photosynthetic pigment contents in the leaves, photosynthesis rates, and chlorophyll fluorescence parameters between the two cotton cultivars, Jianyang Huangmiao and Sumian 16, were examined. The results demonstrated that, the ratio of carotenoids to chlorophylls in Jianyang Huangmiao cotton cultivar was far higher than that in Sumian 16 cotton cultivar, which was why Jianyang Huangmiao cotton cultivar was characterized by the leaf appearance of yellow-green color. Besides, both the maximum net photosynthesis rate and the efficiency of excitation energy capture by open PSII reaction center in Jianyang Huangmiao were higher than those in Sumian 16. Although the differences in electron transport rate downstream QA and quantum yield between the two cotton cultivars were not significant, non-photochemical quenching, density of active PSII reaction center, efficiency of capture per unit area, electron transport rate and energy dissipated in heat in Jianyang Huangmiao cotton cultivar were all lower than those in Sumian 16, indicating that despite the lower chlorophyll content, photosynthetic efficiency in Jianyang Huangmiao cotton cultivar was higher than that in Sumian 16 cotton cultivar.Under high temperature stress the instantaneous net photosynthetic rate in both cotton cultivars decreased significantly. Besides, the electron-involved photorespiration in both cotton cultivars increased markedly. Photorespiration may be the important mechanism of protecting photosynthetic function in cotton under high temperature. High temperature stress caused the decrease in photochemical efficiency of PSII reaction center, activity of reaction center and electron transport rate, meanwhile, the mechanisms of xanthophyll cycle-dependent quenching and state-transition quenching were weakened while the mechanism of reversible inactivation of PSII reaction center was intensified. The mechanism of non-photochemical quenching would be damaged as the temperature rose to some extent. High temperature influenced the initial photochemical reaction in cotton leaves, caused the inactivation of PSII reaction center and damaged the function of both receptor and donor sides of PSII. Furthermore, photosynthetic apparatus were affected greater cell membrane in the two cotton cultivars under high temperature condition. As shown above, the photosynthetic apparatus in Jianyang Huangmiao cotton cultivar was more tolerant than that in Sumian 16 under high temperature stress.