Effect of the opaque-2 gene on accumulation of protein fractions in maize endosperm

The weights of proteins and their solubility fractions per endosperm were determined from 6 maize inbreds and their opaque-2 (o2) versions. Endosperms of o2 inbreds compared to those of isogenic wild typed, on average, contained 44% less true proteins (crude nitrogen minus nonprotein nitrogen), 38% more albumins plus globulins, 60% less zeins, 2% more crude (true + residual) glutelins and 7% more nonzeins. Plotting the weights of zeins per endosperm against those of true proteins allowed the relative accumulation rate of zeins to be evaluated to 0.79 and about 0.55 for wild-type and o2 genotyped, respectively. The contents of protein-bound lysine in proteins, calculated from the weight of nonzeins and their lysine content estimated to 7%, were lower than those reported for total lysine in proteins of o2 endosperms, suggesting a notable contribution of free lysine content in proteins of o2 endosperms was related mainly to the drop in the accumulation of zeins, a slight overproduction of albumins plus globulins and the presence of free lysine.