Enzymatic conversion of dihydroflavonols to flavan-3,4-diols using flower extracts of Dianthus caryophyllus L. (carnation)

Abstract

Flavonoid analysis and supplementation experiments with dihydroflavonols and leucocyanidin on two cyanic, two acyanic and one white/red-variegated flowering strain of Dianthus caryophyllus (carnation) showed that in the acyanic strains recessive alleles (aa) of the gene A interrupt the anthocyanin pathway between dihydroflavonols and leucoanthocyanidins. The instability in the variegated strain involves the same step and is obviously caused by the multiple allele a ^var. In confirmation of these results, dihydroflavonol 4-reductase activity could be demonstrated in enzyme extracts from cyanic flowers and cyanic parts of variegated flowers but not in preparations from acyanic flowers or acyanic parts. The enzyme catalyzes the stereospecific reduction of (+)dihydrokaempferol to (+)-3,4-leucopelargonidin with NADPH as cofactor. A pH optimum around 7.0 and a temperature optimum at 30° C was determined, but the reduction reaction also proceeded at low temperatures. (+)Dihydroquercetin and (+)dihydromyricetin were also reduced to the respective flavan-3,4-cis-diols by the enzyme preparations from carnation flowers, and were even better substrates than dihydrokaempferol.