The distribution of caprylate, caprate and laurate in lipids from developing and mature seeds of transgenic Brassica napus L.

The composition and positional distribution of lipids in developing and mat ure transgenic Brassica napus seeds accumulating up to 7 mol% of caprylate (8.0), 29 mol% caprate (10:0) or 63 mol% of laurate (12:0) were examined. T he accumulation of 8:0 and 10:0 resulted from over-expression of the medium -chain-specific thioesterase (Ch FatB2) alone or together with the respecti ve chain-length-specific condensing enzyme (Ch KASIV). Seeds containing hig h levels of 12:0 were obtained from plants expressing bay thioesterase (BTE ) alone or crossed with a line over-expressing the coconut lysophosphatidic acid acyltransferase (LPAAT), an enzyme responsible for the increase in ac ylation of 12:0 at the sn-2 position. In all instances, 10:0 and 12:0 fatty acids were present in substantial amounts in phosphatidylcholine during se ed development with a drastic decrease of 80-90% in mature seeds. Ar all st ages of seed development however, 8:0 was barely detectable in this membran e lipid. Altogether, these results indicate that these transgenic seeds exc lude and/or remove the medium-chain fatty acids from their membrane and tha t this mechanism(s) is more effective with the shorter-chain fatty acids. F urthermore, seeds of 8.0- and 101:0-producing lines had only negligible lev els of these fatty acids present in the sn-2 position of the triacylglycero ls. In contrast, all 12:0-producing seeds had a substantial amount of this fatty acid in the sn-2 position of the triacylglycerols, suggesting that th e endogenous LPAAT is able to acylate 12:0 if no other acyl-CoA species are available.