Effect of alleles governing 16 : 0 concentration on glycerolipid composition in developing soybeans

Soybean [Glycine max (L.) Merr.] oil typically contains 11% palmitic acid, but germplasm with recessive alleles at Fap gene loci exhibit from less tha n 4% to about 35% 16:0. Although these alleles are used to develop new cult ivars, little is known about how they influence palmitic acid concentration . One theory suggests that fap alleles may mediate differences in triacylgl ycerol composition through genetic effects on the activity or substrate spe cificity of acyltransferases, such as diacylglycerol acyltransferase (EC 2. 3.1.20). Based on logistic function analysis of developing seed, difference s in fap allele expression are evident in the rate of palmitic acid accumul ation in triacylglycerol, with peak deposition near mid-seed fill. Acetate saturation kinetics also reveal a strong positive relation between the rela tive amount of de novo palmitic acid synthesis and the indigenous palmitic acid concentration in triacylglycerol among fap genotypes. However, no diff erences appear in the kinetics of palmitoyl-CoA metabolism in developing se ed of these genotypes. Therefore, the lap alleles apparently do not en code or regulate the activities of glycerolipid acyltransferase enzymes. Rather , major genetic effects on triacylglycerol composition accrue through regul ation of palmitic acid production in the plastids of developing soybean cot yledons.