Résumé
A genetic locus, Anp, controls anthocyanin accumulation in the epidermal cell layers of bean (Phaseolus vulgaris L.) pods and pulvini, and in the standard petals of bean flowers. The expression of the Anp-dependent phenotype requires normal purple pigmentation of the hypocotyl and of the cotyledons. In the Anp-deficient bean genotype, La Victoire, the mRNA transcripts of chalcone synthase and chalcone isomerase accumulated to levels comparable to those of the Anp-carrying genotype AFN. The two genotypes had similar amounts of chalcone synthase enzyme in the epidermal cells where anthocyanins are accumulated in AFN, as shown by immunocytolocalization. The genotype La Victoire accumulated low levels of flavones, flavonols and proanthocyanins but absolutely no anthocyanins in the organs in which pigmentation is controlled by Anp. The data indicate that Anp represents a locus involved in the organ-specific expression of the late steps of the anthocyanin pathway.