Characterization of oil body microstructure, accumulation level and chemical composition in walnut fruit during growth

Oil body (OB) is composed of phospholipids, proteins and neutral lipids. However, the changes of these components in walnut OB (WOB) during walnut growth have not been studied. In this paper, CLSM, TEM and LC-MS/MS were used to observe and quantify the microstructure, accumulation level and biochemical composition of WOB during the growth of walnut (Wen 185 cultivar). The results showed that WOB accumulated near the cell wall on day 60 and then toward the center of cell until it occupied the entire cell on day 88. Afterwards, the WOB began to grow and fuse. Analysis of the chemical composition of WOB indicated that phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, and phosphatidylserine and oleosins, caleosins, and steroleosins made up the WOB membrane. The core of the WOB consisted of 22 free fatty acids and monoacylglycerol, diglyceride, triglyceride. Phosphatidylcholine, triglyceride and oleosin contents continued to increase. The contents of phosphatidylglycerol, unsaturated fatty acids, caleosins and steroleosins continued to decline. The content of phosphatidylethanolamine, phosphatidylinositol and phosphatidylserine remained basically unchanged. These findings provided a basis for understanding the dynamic pattern of WOB bioaccumulation in walnut kernel at different developmental stages. [Display omitted] •WOB began to form at 60–88 DAP and accumulate at 102–130 DAP.•WOB were first formed near cell wall, and gradually occupied cell as they accumulate.•WOBs might grow by mutual fusion within cells.•WOB mainly comprised five phospholipids, three proteins, three neutral lipids and 22 FFA.•PC, TG and oleosin contents continued to increase. PG, UFA, caleosins and steroleosins contents continued to decline.