The B-ring hydroxylation pattern of intermediates of anthocyanin synthesis in pelargonidin-and cyanidin-producing lines of Matthiola incana

In flowers of Matthiola incana, the B-ring hydroxylation pattern of anthocyanins is controlled by the locus b. Recessive genotypes produce pelargonidin and genotypes with wild-type alleles cyanidin as the aglycone. Supplementation experiments on acyanic flowers using extracts of pelargonidin-and cyanidin-producing flowers, respectively, showed not only the presence of compounds with a precursor function for anthocyanin synthesis in the cyanic flowers but also differences in the B-ring hydroxylation pattern of these compounds. Chromatographic investigations proved that flavanones and dihydroflavonols occur in extracts of cyanic flowers. Naringenin, dihydrokaempferol, and their 7-glucosides could be demonstrated in all flower extracts, but in extracts of cyanidin-producing flowers, dihydroquercetin and a further 3′, 4′-hydroxylated dihydroflavonol, tentatively identified as dihydroquercetin 3-glycoside, were additionally found. In no case, however, could eriodictyol be detected. From these results and from the ready hydroxylation of dihydrokaempferol to dihydroquercetin in a white mutant line of Matthiola incana, it can be concluded that introduction of the 3′-hydroxyl group of anthocyanins is not achieved by specific incorporation of caffeic acid during synthesis of the flavonoid skeleton, but by hydroxylation at the dihydroflavonol stage.