FATTY-ACID DISTRIBUTION AND LIPID-METABOLISM IN DEVELOPING SEEDS OF LAURATE-PRODUCING RAPE (BRASSICA-NAPUS L.)

The fatty acid composition and content of membrane and storage lipids of two transgenic laurate-producing rape (Brassica napus L.) lines wer e monitored during seed development. The two lines, the medium-laurate (ML) line and the high-laurate (HL) line, accumulated 34 mol% and 55 mol% of laurate in their seed triacylglycerols, respectively. The diac ylglycerols contained about 17 and 33 mol% of laurate in the ML- and H L-lines, respectively, from the mid-stage of seed development up to se ed maturity. The ML-line showed a maximal relative laurate content in phosphatidylcholine (17 mol%) at the mid-stage of seed development whe reafter the content decreased to 2.7 mol% with seed maturity. The laur ate content in phosphatidylcholine was observed to remain high (26 mol %) in the HL-line from the mid-stage to the end of triacylglycerol dep osition. Thereafter, the relative content decreased and reached 6.6 mo l% in the mature seeds. There was an enhanced activity of lauroyl-phos phatidylcholine-metabolizing enzymes in the seed membranes from laurat e-producing lines compared with control lines, which might explain the decrease seen in laurate content in phosphatidylcholine during seed m aturation. A comparison of the laurate distribution in the lipids from developing laurate-producing rape seeds and developing seeds from thr ee species naturally accumulating laurate at similar levels revealed d ifferences in laurate metabolism compared with these species. The resu lts suggest that phospholipids and triacylglycerols are synthesized fr om the same diacylglycerol pool in rape seeds and that rape lysophosph atidic acid acyltransferase and diacylglycerol acyltransferase do not have the same preference for laurate substrates as the corresponding e nzymes in seed tissues naturally accumulating this acyl group. III add ition, the mechanisms that specifically remove or exclude laurate from membrane lipids appear less effective in rape seed than in tissues na turally evolved to synthesize laurate-rich oils.