Genetic instability of anthocyanin production in Impatiens balsamina.

It is established that in a naturally occurring variegated Impatiens balsamina the phenotype is determined by a mutable allele p (m), of an anthocyanin-governing gene P (r). The special allele produces an acyanic phenotype like the stable recessive p but undergoes frequent changes to P (r) in somatic and germinal cells (causing a variegated phenotype in the former) when a controlling element M is also present in the genome. It is suggested that p (m) is a repressed p (r) and M acts either by removing or inactivating whatever causes that repression. Such changes proceed in a unique fashion: either p (m) changes to p (r) or to an intermediate labile condition P' which then changes to p (r), resulting either in dark or pale, or dark super-imposed on pale, sectors; a reverse situation was not observed. Colourless plants which occasionally appear in unstable lines seem to be due to loss of M although changes ofp (m) itself cannot be ruled out at present.