Sb. Settlage et al., RELATION BETWEEN DIACYLGLYCEROL ACYLTRANSFERASE ACTIVITY AND OIL CONCENTRATION IN SOYBEAN, Journal of the American Oil Chemists' Society, 75(7), 1998, pp. 775-781
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.