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 classes. The molecular species of phosphatidylcholine, diacylglycerols and triacylglycerols were analyzed. After [C-14]oleate feeding differences were found in the labelling of phosphatidylcholine and diacylglycerols labelled molecular species, whereas distribution of these molecules was the same when [C-14]linoleate was supplied. The role of phosphatidylcholine-diacylglycerol interconversion that may be catalysed by CDP choline:diacylglycerol phosphotransferase (EC 2.7.8.2) in generating triacylglycerols rich in linoleate is discussed. All the results obtained corroborate previous studies involving phosphatidylcholine in the biosynthesis of such triacylglycerols and allowed us to suggest reactional mechanisms for the formation of the different triacylglycerols molecular species in sunflower seeds. (C) 1999 Elsevier Science Ltd. All rights reserved.