Flavonol Synthase Activity and the Regulation of Flavonol and Anthocyanin Biosynthesis during Flower Development in Dianthus caryophyllus L. (Carnation)

Flavonol synthase (FLS) was demonstrated in crude extracts from flower buds o f Dianthus caryophyllus (carnation). The enzyme catalyzed the conversion o f dihydrokaempferol and dihydroquercetin to kaempferol and quercetin, respectively. The reaction required 2-oxoglutarate, ferrous ion and ascorbate as co-factors and had a pH optimum at about 7.4. The demonstration o f FLS activity allowed comparative studies on flavonol and anthocyanin biosynthesis during bud and flower development. Besides FLS the flavonoid enzymes chal­ cone synthase (CHS), flavanone 3-hydroxylase (FHT) and dihydroflavonol 4-reductase (D FR ) were measured. D FR is specifically involved in anthocyanin synthesis, while CHS and FHT provide dihydroflavonol, the comm on substrate for both FLS and D FR . Maximum ex­ pression o f CHS, FHT and FLS activity was already observed in small buds, whereas DFR activity started to increase much later and reached its highest level in opened flowers. A sub­ stantial correlation was observed between the time courses o f FLS and D FR activity and the accumulation o f flavonols and anthocyanins, respectively. The competition o f FLS and DFR for dihydroflavonols was found to be largely circumvented by different substrate specificities and by the sequential expression o f the two enzymes. Both flavonols and anthocyanins are obviously not, or only to some extent, subject to degradation.