Increases of Unsaturated Fatty Acids in Membrane Lipids Protects Photosystem II from Photoinhibition under Salinity in Different Halophytes

For the purpose of testing the function of unsaturated fatty acids in different halophytes in the process of photosynthesis under salt stress, the impact of saline stress on plant development, content of chlorophyll, the PSII photochemistry efficiency, content of membrane lipid and composition of fatty acid were investigated in the three halophytes Thellungiella halophila, Limonium bicolor and Suaeda salsa and non-halophyte Arabidopsis thaliana. Salinity (200 mM NaCl) did not reduce the value of Fv/Fm, ØPSII, and chlorophyll content in the halophytes. While all of them decreased by 200 mM NaCl treatment in A. thaliana. In the non-halophytic, A. thaliana, when treated with NaCl, the content of unsaturated fatty acid and the DBI of membrane lipids MGDG, SQDG, PG and PC decreased. While the unsaturated fatty acid content and the DBI of T. halophila, L. bicolor and S. salsa increased. The DBI of total lipids increased in all halophytes but decreased in the non-halophyte, A. thaliana. The proportion of PG increased in T. halophila and S. salsa. It decreased in L. bicolor and A. thaliana. The DGDG (digalactosyldiacylglycerols)/MGDG (monogalactosyldiacylglycerols) ratio of S. salsa increased from 1.20 to 1.35, while it decreased in T. halophila, L. bicolor and A. thaliana under salt stress. These results suggest that unsaturated fatty acid levels increase in the halophytes under salt stress relative to the non-halophyte A. thaliana. The proportion of membrane lipids and unsaturated fatty acids is related to different levels of salt tolerance among different halophytes.