Supply of fatty acid is one limiting factor in the accumulation of triacylglycerol in developing embryos

The metabolic factors that determine oil yield in seeds are still not well understood. To begin to examine the limits on triacylglycerol (TAG) product ion, developing Cuphea lanceolata, Ulmus carpinifolia, and Ulmus parvifolia embryos were incubated with factors whose availability might limit oil acc umulation. The addition of glycerol or sucrose did not significantly influe nce the rate of TAC synthesis. However, the rate of C-14-TAG synthesis upon addition of 2.1 mM C-14-decanoic acid (10:0) was approximately four times higher than the in vivo rate of TAG accumulation in C. lanceolata and two t imes higher than the in vivo rate in U. carpinifolia and U. parvifolia. In C. lanceolata embryos, the highest rate of C-14-TAG synthesis (14.3 nmol h( -1) embryo(-1)) was achieved with the addition of 3.6 mM decanoic acid. C-1 4-Decanoic acid was incorporated equally well in all three acyl positions o f TAG. The results suggest that C. lanceolata, U. carpinifolia, and U. parv ifolia embryos have sufficient acyltransferase activities and glycerol-3-ph osphate levels to support rates of TAG synthesis in excess of those found i n vivo. Consequently, the amount of TAG synthesized in these oilseeds may b e in part determined by the amount of fatty acid produced in plastids.