Abstract
Diacylglycerol acyltransferase (EC 2.3.1.20) activity was assayed during the maturation of seeds of oilseed rape (Brassica napus L.) and safflower (Carthamus tinctorius L.). Developmental studies were also conducted with microspore-derived embryos of oilseed rape (B. napus L. cv Topas) and an embryogenic microspore-derived cell-suspension culture of winter oilseed rape (B. napus L. cv Jet Neuf). In the maturing seeds, diacylglycerol acyltransferase activity increased to a maximum during rapid accumulation of lipid and declined, thereafter, with seed maturity. In microspore-derived embryos of oilseed rape (cv Topas), high levels of diacylglycerol acyltransferase activity were found throughout the early torpedo to late cotyledonary developmental stages with maximum enzyme specific activity associated with the mid-cotyledonary developmental stage. The cell-suspension culture of winter oilseed rape (cv Jet Neuf) contained 3 to 4% triacylglycerol on a dry weight basis and represented about half of the total lipid. The fatty acid profile of total lipid and triacylglycerol in the cell-suspension culture was similar in samples taken during a 1-year period. The Jet Neuf culture contained diacylglycerol acyltransferase with specific activity similar to that of Topas microspore-derived embryos. Jet Neuf diacylglycerol acyltransferase also displayed an enhanced specificity for erucoyl-CoA over oleoyl-CoA when assayed with 14 [mu]M acyl-coenzyme A in the reaction mixture. The specific activity of diacylglycerol acyltransferase in homogenates prepared from the Jet Neuf culture ranged from 5 to 15 pmol of triacylglycerol min-1 mg-1 of protein when assayed at intervals during a period of 1 year. Thus, the cell-suspension culture may represent an attractive tissue source for purification and characterization of triacyl-glycerol biosynthetic enzymes.