The a2m(r-Pa-Pu) Allele of the En-Controlling Element System in Maize

The Enhancer (En) controlling element system in maize includes numerous alleles, one of which, a2m(r-pa-pu), was recovered as a derivative of the a2m(1 1511) allele. The behavior and composition of this allele is described. In the presence of the independently inherited regulatory element, En, the a2m(r-pa-pu) allele mutates and expresses in the aleurone purple, pale and colorless sectors within a colorless background. In the absence of En, the pigmentation is uniformly pale. Colored and colorless germinal mutations of the a2m(r-pa-pu) allele were recovered, although the derivative alleles tested did not respond to En. Uniformly colored derivatives, designated A2', arise only from states of a2m(r-pa-pu) that respond to an active En at relatively early stages in plant development, suggesting that somatic and germinal mutations may arise through similar events. Mutations to A2-expressing alleles appear to occur relatively late in plant development, that is, at or near meiosis, since recognizable mutant sectors do not appear on testcross ears. Kernels exhibiting such mutants are randomly distributed over the ear. The resulting A2' alleles express pigmentation ranging in a continual sequential series from dark pale to intense purple.