Distinct Substrate Specificity of Dihydroflavonol 4-Reductase from Flowers of Petunia hybrida

D ihydroflavonol 4-reductase from Petunia flowers ca ta ­ lyzes the reduction of d ihydroquercetin to leucocyanidin and , in particular, of dihydrom yricetin to leucodelphinid in , w hereas reduction of the simple dihydroflavonol dihydrokaem pferol to leucopelargonidin could not be observed. This special substra te specificity o f d ihydroflavonol 4-re­ ductase is most p robably the reason for the observations th at delphinidin derivatives are the m ain end products of anthocyanin biosynthesis in Petunia flowers, w hereas anthocyanins based on pelargonidin are rarely found and, if p resen t, are only form ed in very small am ounts.