Does triacylglycerol biosynthesis require diacylglycerol acyltransferase (DAGAT)?

Microsomal membrane preparations from the developing seeds of sunflower (Helianthus annuus L.) catalyse the conversion of sn-glycerol-3-phosphate and acyl-CoA to triacylglycerol via phosphatidic acid and diacylglycerol. The formation of diacylglycerol from phosphatidic acid was Mg2+ dependent and in the presence of EDTA phosphatidic acid accumulated. This property was used to generate large quantities of endogenous radioactive phosphatidic acid in the membranes. On addition of Mg2+ the phosphatidic acid was used in triacylglycerol formation. Acyl-CoA had little effect on the label which accumulated in triacylglycerol from phosphatidic acid. Diacylglycerol acyltransferase, therefore, may not play a major role in oil formation as originally envisaged and other enzymes, including diacylglycerol:diacylglycerol transacylase [Stobart, Mancha, Lenman, Dahlqvist and Stymne (1997) Planta 203, 58-66] may have important biosynthetic functions.