PHENOTYPIC EFFECTS OF OPAQUE2 MODIFIER GENES IN NORMAL MAIZE ENDOSPERM

The opaque2 modifier genes convert the soft, chalky endosperm, as foun d in maize opaque2 mutants, to a hard, vitreous phenotype. Modified op aque2 genotypes, also known as Quality Protein Maize (QPM), have incre ased levels of the essential amino acid lysine and a normal appearing kernel. The development of vitreous endosperm in QPM is associated wit h a two-to-threefold increase in the gamma-zein storage protein. To de termine whether an increase concentration of gamma-zein can influence hardness and the formation of vitreous endosperm in normal genotypes, we derived 13 modified normal inbreds from a cross of the normal line W64A with Pol 34 QPM. Analysis of protein content, kernel density and hardness revealed variation among the 13 inbreds. The modified normal inbreds show an increase content of gamma-zein in the endosperm, simil ar to that of QPM. But the high level of gamma-zein did not increase h ardness and density above a threshold level. The modified normal inbre ds did not have an increase lysine content, suggesting modifier genes, per se, do not improve the nutritional quality of maize endosperm.