RELATION BETWEEN DIACYLGLYCEROL ACYLTRANSFERASE ACTIVITY AND OIL CONCENTRATION IN SOYBEAN

Diacylglycerol acyltransferase (EC 2.3.1.20; DGAT) catalyzes synthesis of triacylglycerol from acyl-CoA and diacylglycerol. Activity of this enzyme and developmental changes in oil accumulation were estimated a t various stages of seed growth in soybean germplasm with phenotypic d ifferences in oil content. Oil deposition in seed of these genotypes f ollowed a sigmoid pattern that was modeled to predict incremental rate s of oil accumulation during seed development. A strong positive corre lation was found between the estimated peak rate of oil deposition (ne ar the mid-term of seed development) and oil concentration in mature s eed. At saturating substrate levels, DCAT activity measured near the p eak rate of oil deposition also was correlated positively with oil phe notype. In the latter stages of seed development, a positive correlati on between estimates of enzyme activity at or below the apparent K-m f or diolein and comparable oil accumulation rates was attributed to red uced synthesis of substrates and/or potential change in affinity for s ubstrate as suggested by an increase in apparent K-m for diolein in ol der seed. These data indicated that DCAT activity may be a rate-limiti ng step in triacylglycerol synthesis. However, it is difficult to acce pt the idea of a single rate-limiting step at the end of a complex met abolic pathway. Because oil is a quantitatively inherited trait, sever al genes determine genotypic differences in oil content among soybeans . Hence, DCAT activity may be an indicator of coordinated genetic expr ession of gene-products in the entire glycerolipid synthetic pathway f or a given genotype. In any case, results of this investigation demons trated that genotypic differences in DGAT activity contributed to expr ession of genetic variation in oil content among soybean germplasm.