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

Abstract

Abstract 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.