Studies on seeds. IV. Lipid composition of bean cotyledon vesicles

Lipid content has been determined for two types of lipid-rich vesicles isolated from bush bean cotyledon at 24 hr of germination. The larger, nonassociating vesicles are four to six times richer in triglyceride than the smaller vesicles which associate strongly among themselves, as well as with smooth membranes in the cell. The larger vesicles contain about 640 micromoles of phospholipid per gram of protein, while the smaller vesicles have only one-half to two-thirds as much phospholipid per gram of protein. The ratio of individual phospholipids in both kinds of vesicles is close to 20% phosphatidylethanolamine, 60% phosphatidylcholine, and 20% phosphatidylinositol. The fatty acid composition of all phospholipids is similar, and quite different from that of triglyceride, which contains twice as much linolenic acid and less than one-fourth as much palmitic acid. Pea cotyledon has quantitatively the same lipid content as bean cotyledon.