Exogenous application of gibberellic acid participates in up-regulation of lipid biosynthesis under salt stress in rice

Alterations in membrane lipid composition lead to improved plant salt tolerance. Gibberellic acid (GA(3)) has also been widely reported to reduce growth inhibition induced by increased salinity. However, little is known about whether exogenous application of GA(3) participates in up-regulation of lipid biosynthesis under salt stress. In this study, one of the major lipid biosynthesis genes in rice (Oryza sativa L. cv. Nipponbare), monogalactosyldiacylglycerol synthase (OsMGD) was found to be significantly up-regulated by GA(3) treatment. Lipid analysis showed that after salt disturbance, the concentrations of all the measured lipids, including monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG) and phospholipid lipids+sulfoquinovosyl diacylglycerol (PL+SQDG) were decreased significantly. However, GA(3) treatment prior to salt disturbance caused those lipids to remain at high levels, as well as preserving a high DGDG/MGDG ratio. The desaturation of DGDG (DBI) was also increased in GA(3) pre-treatment plants as compared with no GA(3) pre-treatment, primarily due to a decrease of 16:0 fatty acids and an increase of 18:3 fatty acids in DGDG. Plants pre-treated with GA(3) prior to salt disturbance had higher dry weights than those without pre-treatment. The chlorophyll concentration was also higher in GA(3) treated plants than in untreated plants under salt disturbance. Taken together, these results indicate that exogenous application of GA(3) participates in up-regulation of chloroplast lipid biosynthesis under salt disturbance in rice.