Leucocyanidin reductase activity and accumulation of proanthocyanidins in developing legume tissues

Proanthocyanidin (PA) and anthocyanin accumulation and location in developing leaves, flowers, and seeds of the legumes Medicago sativa, Lotus japonicus, Lotus uliginosus, Hedysarum sulfurescens, and Robinia pseudacacia were investigated by quantitative measurements and by histological analysis after staining with 1% vanillin/HCl, butanol/HCl, or 50% HCl. M. sativa leaves and flowers, L. japonicus leaves, and R. pseudacacia flowers do not contain PAs, but seeds of all investigated species contain PAs. Anthocyanins are absent in the seed coats of all five species and in leaves of L. japonicus. PA content generally increases as a function of development in leaves, but declines in flowers. With the exception of H. sulfurescens, flower PAs are synthesized in the parenchyma cells of the standard petal, while anthocyanins are located in the neighboring epidermal cells. Leucocyanidin reductase (LCR) catalyzes the conversion of 2,3-trans-3,4-cis-leucocyanidin to (+)-catechin and is the first enzyme in the PA-specific pathway. LCR activity was only detected in PA-containing tissues and generally declined during tissue development.