KMS Institute of soil and water conservation Chinese Academy of Sciences
|Place of Conferral||北京|
|Keyword||单半乳糖甘油二酯 光保护 叶黄素循环 膜脂|
|Other Abstract||Monogalactosyldiacylglycerol (MGDG) is an important component of the thylakoid membrane, accounting for approximately 50% of the thylakoid membrane lipid content, and is essential for plant photosynthesis. Illumination is an indispensable condition for photosynthesis. Photosynthesis systems' multi-level photoprotection and repair mechanism is a response of plants to high-light stress. There are two defense lines in this mechanism: heat dissipation suppression mechanism and phototoxic product removal mechanism. At present, there are many studies on the role of MGDG in salt stress, drought stress and chilling stress. However, the role of MGDG in photoprotection under high-light stress is not clear. In this experiment, rice MGD (OsMGD) gene tobacco (M2, M5) and wild-type tobacco (SR) were used as experimental materials. The light intensity of the two groups was selected according to the measurement of the early photosynthetic curve, and the phenotypic parameters of the tobacco before and after high-light treatment were determined. The photosynthetic parameters, the formation of phototoxic products, xanthophyll cycle efficiency, and membrane lipid content were used to explore the photoprotective mechanism of MGDG on two defense lines. The experimental results are as follows:|
(1) When the light response curve was analyzed, the net photosynthetic rate of the transgenic lines M2 and M5 was increased by 28% and 29%, respectively, and the light saturation point was increased by 38% and 25%, respectively, compared with the wild-type SR tobacco. After one day of high-light treatment, the leaf fresh weights of M2 and M5 were 19% and 21% higher than those of SR respectively. The fresh weight of the whole plant was 11% and 11% higher than that of SR, respectively; the chlorophyll content was 23% and 18% higher than SR, respectively; the net photosynthetic rate are 173% and 172% higher than SR, respectively. From the phenotype, it can be seen that after the high-light treatment, the SR leaves have bleaching spots, the leaves become smaller and thinner, and the color is yellowish, while the leaves of the M2 and M5 lines are less damaged. In summary, the high-light treatment caused photoinhibition of SR, M2, and M5, but the transgenic strain had a stronger high-light tolerance.
(2) After analyzing the fluorescence parameters of tobacco after high-light treatment, the heat dissipation of SR, M2 and M5 after high-light treatment increased by 37%, 81% and 75% respectively; however, the photosynthetic electron transfer rate of SR decreased by 30%. M2 and M5 increased by 23% and 25%, respectively; the photochemical quenching coefficient of SR decreased by 32%, while that of M2 and M5 increased by 24% and 18%. The content of superoxide anion radicals in SR, M2, and M5 increased by 239%, 99%, and 71%, respectively, and the hydrogen peroxide content increased by 57%, 25%, and 33%, respectively, and the malondialdehyde content increased by 27%. 3% and 3%. The above results indicate that the relative electron transfer efficiency and photochemical quenching coefficient of the transgenic strains under high-light stress increase the energy to be converted into assimilating force for dark reaction more quickly through light reaction, and the transgenic strain has higher heat on the other hand. The dissipative ability can quickly convert excess excitation energy into heat loss, thereby reducing the formation of phototoxic products.
(3) Study on the xanthophyll circulation found that the content of violaxanthin in SR, M2, and M5 decreased by 11%, 41%, and 43% after high-light stress, and the content of antheraxanthin decreased by 27%, 32%, and 56% respectively, zeaxanthin content increased 5311%, 26945% and 19916% respectively, and the xanthophyll cycle efficiency increased by 2008%, 5874% and 4658%, respectively. It shows that over-expression of OSMGD in high-light stress enhances the xanthophyll cycle efficiency, and enhances heat dissipation capacity in the first line of defense. The massive production of zeaxanthin scavenges active oxygen at the second line of defense, enhancing the high-light tolerance of transgenic lines.
(4) The difference in high-light tolerance results from the overexpression of the MGD gene. We subsequently studied membrane lipids. The results showed that the MGDG content of SR, M2, and M5 after high-light treatment decreased by 34%, 19%, and 18%, respectively; the DGDG content increased by 11%, 38%, and 24%, respectively, and the PL content decreased by 42%, 15%, and 19%, respectively. The total lipid content decreased by 10%, 2.4%, and 3.9%, respectively; MGDG fatty acid unsaturation decreased by 9%, 4%, and 4%, respectively, and DGDG fatty acid unsaturation decreased by 26%, 11%, and 15%, respectively. PL fatty acid unsaturation decreased by 28%, 7%, and 10%, respectively; MGDG/chlorophyll increased by 28%, 19%, and 12%, DGDG/chlorophyll increased by 9%, 6%, and 4%, respectively; PL/chlorophyll increased by 22%, 16%, and 8%. DGDG/MGDG increased, but the transgenic version was higher than the wild type. The results showed that the high-light treatment resulted in the degradation of membrane lipids, the unsaturation of membrane lipids, and the decrease in thylakoid protein packing density, but the transgenic lines performed better than the wild type
In summary, the increase in monogalactosyl diacylglycerol content in high-light stress increases the xanthophyll cycle efficiency, increases energy dissipation in the first line of defense, and enhances the plant's high-light tolerance; The massive synthesis of zeaxanthin removes the active oxygen, so that the generated reactive oxygen species are eliminated at the second line of defense, and the plant's high light tolerance is improved; the heat dissipation efficiency is increased, the pressure of the photosynthetic system is reduced, and the photosynthetic electron transfer rate and CO2 are promoted. The assimilation rate makes the energy fixed by photosynthesis, reduces the damage of the excess excitation energy to the photosynthetic structure, and improves the plant's high-light tolerance.Photoinhibition caused membrane lipid degradation, membrane fluidity and permeability were destroyed; thylakoid membrane structure and function were impaired, and photosynthetic function of the leaf was destroyed. The conversion of monogalactosyl diglyceride to digalactosyl diglyceride is one of the biofilm response to high-light stress. The double-galactose diglyceride double structure partially compensates for membrane damage and maintains the structure and function of the membrane, increased plant tolerance to high-light stress.
|李倩. 单半乳糖甘油二酯的光保护机理[D]. 北京. 中国科学院大学,2018.|
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