Quantitative dissection of lipid degradation in rice seeds during accelerated aging

Aging during storage negatively affects rice seed viability and nutrition quality. Lipid degradation caused by phospholipase D (PLD) activity is known to be responsible for seed deterioration in Arabidopsis, but the mechanisms of this process in monocotyledonous plant rice remain unclear. In this study, we carried out lipid profiling analysis for rice seeds, and found that the main membrane lipids phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylglycerol (PG) declined during accelerated aging. In contrast, phosphatidic acid (PA), a hydrolysis product produced by PLD, increased. Interestingly, the degree of PA increase induced by accelerated aging (at 2 days) was much higher in rice than that in Arabidopsis (200% vs. 30%). Moreover, the decreased molecular species in PC and PE were well fit with those that were increased in PA, suggesting that PA may be derived from PLD-mediated lipid hydrolysis. OsPLDα1 and α3 were the major PLDαs in rice seeds, and their transcription increased significantly during the aging process. The aging treatment induced OsPLDα protein expression and activation. Three lipoxygenases (LOXs) were analyzed, and OsLOX2 transcription was induced significantly during seed aging. Our results reveal detailed information regarding lipid degradation during rice seed aging, and we go on to discuss the relationship between lipid degradation and peroxidation during seed aging.