Differences in corn endosperm proteins in developing seeds of normal and opaque-2 corn

The effects of the opaque-2 (o2) mutation on the composition of corn endosperm proteins and their relative rates of synthesis during seed development were investigated by sodium dodecyl sulfate polyacrylamide electrophoresis (SDS-PAGE) and two-dimensional electrophoresis. Nonprotein nitrogen, albumins and globulins, zeins, alcohol-soluble reduced glutelins (ASG), and alcohol-insoluble reduced glutelins (AIG) were sequentially extracted from ground endosperm dissected from corn kernels harvested at 18, 22, 30, and 48 days after pollination. In early stages of normal genotype, nonprotein nitrogen, albumins, and globulins were present at high levels. These components declined in amount, and levels of zein, ASG, and AIG were elevated during maturation. In the o2 grain, the level of zein did not rise as high, and the final amount of AIG was higher than that of normal endoserpm. Compositions of albumin and globulin proteins, as shown by SDS-PAGE, were similar at the same signs of grain development in normal and o2 corns, except that albumins of normal endosperm contained, at all stages, a protein absent in o2 albumins. Zein, upon SDS-PAGE, showed less of the higher molecular weight protein in the o2 genotype. Two-dimensional electrophoresis (isoelectric focusing in the first direction, pH 3.5 aluminum lactate PAGE in the second) showed that o2 corn lacked several zeins present in normal and other mutant genotypes. SDS-PAGE indicated that certain albumins and globulins diminished during maturation of both normal and o2 kernels. ASG, like zein, did not change in SDS-PAGE pattern during maturation. AIG patterns of certain components became more intense during kernel development, indicating that these proteins are synthesized mainly during maturation. These changes were discussed with respect to effects of the o2 genes on kernel composition and structure.