Remodelling of triacylglycerols in microsomal preparations from developing castor bean (Ricinus communis L.) endosperm

Microsomal preparations from developing castor bean (Ricinus communis L.) endosperm catalyzed remodelling of in-situ-formed triacylglycerol (TAG) species. Castor bean microsomal membranes synthesized ¹⁴C]TAGs from either glycerol 3-phosphate and ¹⁴C]ricinoleoyl-CoA or ¹⁴C]glycerol 3-phosphate and ricinoleoyl-CoA. Upon repelleting and subsequent incubation of the microsomes a redistribution occurred of both the ¹⁴C]glycerol and ¹⁴C]ricinoleoyl moieties of the in-situ-synthesized ¹⁴C]TAGs. Radioactivity was transferred from TAG species with three (3HO-TAG) or two (2HO-TAG)ricinoleoyl groups into species with two or one (HO-TAG) ricinoleoyl groups. Mass analysis of the lipid and fatty acid movements in the membranes showed that a net synthesis of TAGs with no, one and two ricinoleoyl groups occurred at the expense of 3HO-TAG and polar lipids. Thus, the non-hydroxylated acyl groups from polar lipids were used in the remodelling of TAGs. In-vivo feeding of ¹⁴C]ricinoleic acid to slices of castor bean endosperm demonstrated the presence of two radioactive pools of TAGs one in the oil bodies, which was rich in ¹⁴C]3HO-TAG, and one associated with the microsomal membranes, which was dominated by radioactive 1HO-TAG and 2HO-TAG. The microsomal TAG pool was remodelled in vivo in a similar way as in the in-vitro experiments with microsomal membranes. Received: 8 November 1996 / Accepted: 5 February 1997