Biosynthesis of triacylglycerols by developing sunflower seed microsomes

In order to elucidate the biochemical pathway involved in the formation of plant triacylglycerols rich in C-18 polyunsaturated fatty acids, microsomes from developing sunflower cotyledons were incubated with [1-C-14]oleate or [1-C-14]linoleate. Total lipids were extracted and separated into lipid cl asses. The molecular species of phosphatidylcholine, diacylglycerols and tr iacylglycerols were analyzed. After [C-14]oleate feeding differences were f ound in the labelling of phosphatidylcholine and diacylglycerols labelled m olecular species, whereas distribution of these molecules was the same when [C-14]linoleate was supplied. The role of phosphatidylcholine-diacylglycer ol interconversion that may be catalysed by CDP choline:diacylglycerol phos photransferase (EC 2.7.8.2) in generating triacylglycerols rich in linoleat e is discussed. All the results obtained corroborate previous studies invol ving phosphatidylcholine in the biosynthesis of such triacylglycerols and a llowed us to suggest reactional mechanisms for the formation of the differe nt triacylglycerols molecular species in sunflower seeds. (C) 1999 Elsevier Science Ltd. All rights reserved.