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

Abstract

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

Figure 1

TAG accumulation and percentage of decanoic acid in TAG in developing embryos of C. lanceolata, U. carpinifolia, and U. parvifolia. Twenty embryos at each stage were analyzed for TAG content. The left scale represents the TAG content (♦), and the right scale represents the percent of decanoic acid in TAG (▴).

Figure 2

Rate of ¹⁴C-TAG synthesis under different conditions. A, Ten pairs of cotyledons incubated in 0.2 mL of phosphate buffer (pH 7.2) with ¹⁴C-decanoic acid at the concentrations indicated. B, Ten pairs of cotyledons incubated in 2.1 mm ¹⁴C-decanoic acid plus 0.2 mL of phosphate buffer ranging in pH from 6 to 8.