Involved in the biosynthesis of condensed tannins. Converts cyanidin into (-)-epicatechin as the major product. a (2R,3R)-flavan-3-ol + 2 NAD(+) = an anthocyanidin with a 3-hydroxy group + 2 H(+) + 2 NADH a (2R,3R)-flavan-3-ol + 2 NADP(+) = an anthocyanidin with a 3-hydroxy group + 2 H(+) + 2 NADPH Inhibited by (+)-catechin, quercetin and (+)- and (-)-dihydroquercetin. Not inhibited by salt. Positive cooperativity with NADPH acting as cosubstrate and modulator. cannot use NADH as cosubstrate. Optimum pH is 8.0. Optimum temperature is 55 degrees Celsius. Secondary metabolite biosynthesis; flavonoid biosynthesis. Homo- or heterodimer. Flowers and young siliques. Detected specifically in the endothelium of seed coat. From fertilization until pre-globular embryo stage. Regulated by TRANSPARENT TESTA 2, TRANSPARENT TESTA 8 and TRANSPARENT TESTA GLABRA 1. Belongs to the NAD(P)-dependent epimerase/dehydratase family. Dihydroflavonol-4-reductase subfamily.