Analysis of the Three Essential Constituents of Oil Bodies in Developing Sesame Seeds

Oil bodies of plant seeds contain a matrix of triacylglycerols surrounded by a monolayer of phospholipids embedded with alkaline proteins termed oleosins. Triacylglycerols and two oleosin isoforms of 17 and 15 kDa were exclusively accumulated in oil bodies of developing sesame seeds. During seed development, 17 kDa oleosin emerged later than 15 kDa oleosin, but it was subsequently found to be the most abundant protein in mature oil bodies. Phosphotidylcholine, the major phospholipid in oil bodies, was amassed in microsomes during the formation of oil bodies. Prior to the formation of these oil bodies, a few oil droplets of smaller size were observed both in vivo and in vitro. These oil droplets were unstable, presumably due to the lack of steric hindrance shielded by the oleosins. The temporary maintenance of these droplets as small entities seemed to be achieved by phospholipids, presumably wrapped in ER. Oil bodies assembled in late developing stages possessed a higher ratio of oleosin 17 kDa over oleosin 15 kDa and were utilized earlier during germination. It seems that the proportion of oleosin 17 kDa on the surface of oil bodies is related to the priority of their utilization.