A Comparison of the Metabolic Fate of Fatty Acids of Different Chain Lengths in Developing Oilseeds

Abstract

To determine if medium and long chain fatty acids can be appropriately metabolized by species that normally produce 16 and 18 carbon fatty acids, homogenates of developing Cuphea wrightii, Carthamus tinctorius, and Crambe abyssinica seeds were incubated with radiolabeled lauric, palmitic, oleic, and erucic acids. In all three species, acyl-CoA synthetase showed broad substrate specificity in synthesis of acyl-coenzyme A (CoA) from any of the fatty acids presented. In Carthamus, two-to fivefold less of the foreign FAs, lauric, and erucic acid was incorporated into acyl-CoAs than palmitic and oleic acid. Lauric and erucic acid also supported less glycerolipid synthesis in Carthamus than palmitic and oleic acid, but the rate of acyl-CoA synthesis did not control rate of glycerolipid synthesis. In all species examined, medium and long chain fatty acids were incorporated predominantly into triacylglycerols and were almost excluded from phospholipid synthesis, whereas palmitic and oleic acid were found predominantly in polar lipids. However, the rate of esterification of unusual fatty acids to triacylglycerol is slow in species that do not normally synthesize these acyl substrates.

Triacylglycerol Bioassembly in Microspore-Derived Embryos of Brassica napus L. cv Reston

“…These data are consistent with oleoyl incorporation into TAGs via the Kennedy Pathway, as well as into membrane lipid components (e.g. PCs, PEs), as is known for zygotic oilseeds (7,28,30,44,45). In particular, the rates of incorporation of 18:1 moieties into LPA, PA, and in developing safflower (25) and cultured rat hepatocytes (15,26), respectively.…”

Medium-chain fatty acid biosynthesis and utilization in Brassica napus plants expressing lauroyl-acyl carrier protein thioesterase

“…In leaves, almost all fatty acids are directed toward membrane production. Because membrane acyl-chain composition is a critical component of membrane function, cells apparently have evolved strict mechanisms to prevent substantial incorporation of unusual fatty acids such as 12:0 (Battey and Ohlrogge 1989). Such mechanisms include acyltransferase specificities which exclude unusual fatty acids (Oo and Huang 1989) and phospholipases which remove unusual fatty acids if incorporated into phospholipids (Banas et al 1992).…”

“…However, in some plant species unusual fatty acids may occur as the major fatty acids of storage triacylglycerols in seed oils. Despite extensive accumulation of such unusual fatty acids in seeds they generally do not occur in leaf tissue and leaf plastids do not express the unique proteins necessary for their synthesis (Battey and Ohlrogge 1989;Somerville and Browse 1991). For example, seeds of the California bay produce predominantly laurate (12:0) and decanoate (10:0) (Hilditch and Williams 1964).…”

“…Leaves synthesize long-chain fatty acids predominantly to support galactolipid and phospholipid production, and the resultant lipids are then used as building blocks for membranes (Harwood 1988;Battey and Ohlrogge 1989;Somerville and Browse 1991). The physical properties of cellular membranes are influenced by both the chain length and the degree of unsaturation of component fatty acids (Lynch and Thompson 1984).…”

Biosynthesis of Acyl Lipids Containing Very-Long Chain Fatty Acids in Microspore-Derived and Zygotic Embryos of Brassica napus L. cv Reston

“…Although it is clear that in higher plants, C16 and C18 fatty acids are incorporated into TAGs via the G-3-P pathway according to Kennedy (5,24), the mechanism involved in the biosynthesis of TAGs containing VLCFAs is not fully understood, despite a number of studies to elucidate the pathway in various developing oilseeds (4,6,7,13,18,25). Recently, however, it was suggested that the biosynthesis of TAGs containing VLCFAs in L. annua and S. alba occurs via a mechanism involving rapid elongation of 18:1-CoA in the presence of malonyl-CoA to yield 20:1, 22:1, and 24:1 moieties, which are subsequently incorporated into TAGs via the Kennedy pathway (14).…”