Genetic Control of Flavanone 3-Hydroxylase Activity and Flavonoid 3-′Hydroxylase Activity in Antirrhinum Majus (Snapdragon)

In flower extracts of defined genotypes of Antirrhinum majus, two different hydroxylases were found catalysing the hydroxylation of naringenin and eriodictyol in the 3-position and of naringenin in the 3′-position. The 3-hydroxylase is a soluble enzyme and belongs according to its cofactor requirement to the 2-oxoglutarate-dependent dioxygenases. Investigations on different genotypes revealed a clear correlation between block of the anthocyanin pathway by recessive alleles of the gene inc and a complete lack of 3-hydroxylase activity. Chemogenetic studies on different genotypes suggested that the 3′-hydroxyl group of the B-ring of flavonoids is introduced at the stage of C₁₅ intermediates. The corresponding 3′-hydroxylase was found to be localized in the microsomal fraction and required NADPH as cofactor. In confirmation of the chemogenetic studies, a strict correlation was found between 3′-hydroxylase activity and the gene eos which is known to control the hydroxylation of flavones, flavonols and anthocyanins in the 3′-position. These results are similar to those previously obtained with Matthioia incana.