| As an important cash crop, tomato (Lycopersicon esculentum mill.) is a world-wide distribution. Salt stress can damage the structure and function of thylakoid membrane, causing the decrease of photosynthesis, but the increase of unsaturated fatty acid of thylakoid membrane can enhance the ability of photosynthesis of plants. The dominant factor determining the level of cis-unsaturated fatty acids in PG is the substrate selectivity of glycerol-3-phosphate acyltransferase(LeGPAT)in tomato chloroplasts, which prefers 18:1-ACP to 16:0-ACP as a substrate. Therefore, a large proportion of oleic acid (18:1) occurs at the sn-1 position of PG in tomato, and under salt stress, oleic acid (18:1) of sn-1 position desaturates further into cis-polyunsaturated fatty acids of linoleic acid (18:2) and linolenic acid (18:3) by acyl-fatty acid desaturase in thylakoid membranes.In order to investigate the relationship of fatty acid composition of PG in thylakoid membrane and the tolerance to salt stress, WT, sense transgenic lines T2-19(+), T2-5(+) and antisense transgenic lines T2-16(-), T2-2(-) of tomato were used to determine the fatty acid composition of thylakoid membrane, the fatty acid composition of PG, photosynthetic and chlorophyll fluorescence parameters, the production of chloroplastic reactive oxygen species (ROS) and activities of antioxidase in chloroplasts, and the repair of D1 under salt stress.The results showed as follows:1. The results showed that there was no significant difference about the unsaturated fatty acids composition of digalactosyldiacylglycerol (DGDG), monogalactosyldiacylglycerol (MGDG) and sulfoquinovosyldiacylglycerol (SQDG) in wild type (WT) and transgenic plants, but the content of fatty acids of PG changed markedly. Compared with WT, a higher content of 18:2 and 18:3 in PG was detected in sense transgenic plants. In contrast, the decreased unsaturation of PG in antisense transgenic plants was observed. And compared with WT, unsaturated fatty acids of PG increased in sense lines slightly, whereas decreased in WT and antisense ones lightly.2. In order to investigate the correlation of fatty acid composition in thylakoid membrane and the tolerance of photosystem to salt stress, photosynthetic rate (Pn) and the maximal photochemical efficiency of PSII (Fv/Fm) in WT and transgenic plants decreased under salt stress, but compared with WT, Fv/Fm and Pn decreased more obviously in antisense lines, while more slowly in sense ones. It is indicated that the increase of unstaurated fatty acid in PG can stabilize the structure of photosynthetic apparatus, and alleviate the photoinhibition of PSII.3. Compared with WT, the sense transgenic lines could maintain higher activities of chloroplastic SOD and APX, and produce lower content of O2 and H2O2 under salt stress. In contrast, the activities of chloroplastic SOD and APX were lower and the content of ROS was higher in the antisense transgenic plants. Relative to other lines, the higher activities of chloroplastic SOD and APX can scavenge more ROS, and mitigate the extent of lipid peroxidation caused by the accumulation of ROS, and maintain the integrity of the cytomembrane.4. The analysis of western blot indicated that salt stress affected the repair of D1 protein. During short-time salt stress, the total content of D1 protein changed slightly among five lines. During salt stress for a long time, the content of D1 protein decreased in WT and transgenic plants. Compared with WT, there was a higher content of D1 protein in sense transgenic lines and lower level of D1 in antisense ones. After the treatment of streptomycin (SM), the net degradation of D1 was faster in sense trangenic plants and the most slowly in antisense ones. It is demonstrated that the rate of D1 turnover in sense lines was faster than other ones. These results suggested that the increase of unsaturation in PG can enhance the salt tolerance in tomato plants by accelerating the repair of D1 protein and improving the activities of antioxidase in chloroplasts.
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