Selection and characterisation of flavanone 3-hydroxylase mutants ofDahlia, Streptocarpus, Verbena andZinnia

Precursor experiments and chromatographic studies indicate that the hydroxylation of flavanones in the 3-position to dihydroflavonols is blocked in special white-flowering mutants ofDahlia, Streptocarpus, Verbena andZinnia. The result of our investigations was confirmed in as much as the activity of the enzyme flavanone 3-hydroxylase, which catalyses the conversion of flavanones to dihydroflavonols, could readily be detected in flower extracts of cyanic strains of the four plant species. It was found to be, however, completely absent in flower extracts of the corresponding acyanic mutants. Thus, the interruption of the anthocyanin pathway in these mutants is clearly caused by a lack of this enzyme activity. Similar to the enzymes from other sources, the 3-hydroxylases ofDahlia, Streptocarpus, Verbena andZinnia are soluble enzymes; they belong to the 2-oxoglutarate-dependent dioxygenases and the reaction is inhibited by ethylenediaminetetraacetic acid, KCN and diethyldithiocarbamate.