DEVELOPMENTAL PROFILE OF DIACYLGLYCEROL ACYLTRANSFERASE IN MATURING SEEDS OF OILSEED RAPE AND SAFFLOWER AND MICROSPORE-DERIVED CULTURES OF OILSEED RAPE

Diacylglycerol acyltransferase (EC 2.3.1.20) activity was assayed duri ng the maturation of seeds of oilseed rape (Brassica napus L.) and saf flower (Carthamus tinctorius L.). Developmental studies were also cond ucted with microspore-derived embryos of oilseed rape (B. napus L. cv Topas) and an embryogenic microspore derived cell-suspension culture o f winter oilseed rape (B. napus L. cv let Neuf). In the maturing seeds , diacylglycerol acyltransferase activity increased to a maximum durin g rapid accumulation of lipid and declined, thereafter, with seed matu rity. In microspore-derived embryos of oilseed rape (cv Topas), high l evels of diacylglycerol acyltransferase activity were found throughout the early torpedo to late cotyledonary developmental stages with maxi mum enzyme specific activity associated with the mid-cotyledonary deve lopmental stage. The cell-suspension culture of winter oilseed rape (c v Jet Neuf) contained 3 to 4% triacylglycerol on a dry weight basis an d represented about half of the total lipid. The fatty acid profile of total lipid and triacylglycerol in the cell-suspension culture was si milar in samples taken during a 1 -year period. The let Neuf culture c ontained diacylglycerol acyltransferase with specific activity similar to that of Topas microspore-derived embryos. let Neuf diacylglycerol acyltransferase also displayed an enhanced specificity for erucoyl-CoA over oleoyl-CoA when assayed with 14 mum acyl-coenzyme A in the react ion mixture. The specific activity of diacylglycerol acyltransferase i n homogenates prepared from the Jet Neuf culture ranged from 5 to 15 p mol of triacylglycerol min-1 mg-1 of protein when assayed at intervals during a period of 1 year. Thus, the cell-suspension culture may repr esent an attractive tissue source for purification and characterizatio n of triacylglycerol biosynthetic enzymes.