Control of gene action in the synthesis of anthocyanin in maize

Summary R^st is an unstable allele of R that exhibits a mosaic phenotype in the aleurone, consisting of heavily pigmented spots on a colorless background. This variagated phenotype is presumably caused by the frequent somatic reversion of R from an inactive to an active form. Data are presented showing that such a reversion can take place at different times during the plant ontogenesis. Various stippled derivatives have been selected that differ in the number and size of dots formed in the endosperm. The reversion rate of R^st and derivatives toward self-colored (R^sc) has been estimated in the germinal and somatic tissues. This analysis indicates that some of the stippled derivatives differ in their capacity to revert toward R^sc in both the somatic and germ cells. The effect of internal factors on the R^st reversion rate has been measured. On the basis of these data the possible mechanism causing genetic instability of R^st are briefly discussed.This investigation has been partially supported by Consiglio Nazionale delle Ricerche, Roma.