Genetic and biochemical studies on flavonoid 3'-hydroxylation in flowers of Petunia hybrida

In flower extracts of defined genotypes of Petunia hybrida, an enzyme activity was demonstrated which catalyses the hydroxylation of naringenin and dihydrokaempferol in the 3'-position. Similar to the flavonoid 3'-hydroxylases of other plants, the enzyme activity was found to be localized in the microsomal fraction and the reaction required NADPH as cofactor. A strict correlation was found between 3'-hydroxylase activity and the gene Ht1, which is known to be involved in the hydroxylation of flavonoids in the 3'-position in Petunia. Thus, the introduction of the 3'-hydroxyl group is clearly achieved by hydroxylation of C15-intermediates, and the concomitant occurrence of the 3',4'-hydroxylated flavonoids quercetin and cyanidin (paeonidin) in the presence of the functional allele Ht1 is due to the action of one specific hydroxylase catalysing the hydroxylation of common precursors for both flavonols and anthocyanins.