Dihydroflavonol 4-reductase activity is associated with the intensity of flower colors in delphinium

Abstract

Flower color intensity is largely determined by the amount of accumulated anthocyanins. Delphinium flowers show a wide range of colors from pale pink to deep orange to red to dark blue. Here, we demonstrated that the level of anthocyanin accumulation in dark blue, orange and red varieties was higher than in pale blue and pale pink varieties. Since dihydroflavonol 4-reductase (DFR) is a key enzyme in anthocyanin biosynthesis and accumulation in plants, we investigated the relationship between flower color intensity and the level of DFR gene expression. Six delphinium varieties with different flower colors were analyzed. Varieties that accumulated relatively high levels of anthocyanin also had high levels of DFR expression and enzyme activity in crude protein extracts. By contrast, DFR expression and activity was low in varieties with low anthocyanin accumulation. Alignment of DFR amino acid sequences in the six varieties showed the presence of two types, termed DgDFR and DnDFR. Recombinant DgDFR and DnDFR proteins had similar substrate specificities, but the kinetic turnover rate of the DnDFR enzyme was higher than that of DgDFR. We conclude that DFR expression level is closely correlated with flower color intensity and that DFR is an important factor that determines anthocyanin accumulation and delphinium flower color intensity.