Changes in anthocyanin content and composition of developing storage root of purple-fleshed sweet potato (Ipomoea batatas (L.) Lam)

The changes in the content and composition of anthocyanin in the developing storage root of 10 purple-fleshed sweet potato clones were investigated in order to elucidate the pattern of anthocyanin accumulation between clones with a high and low anthocyanin content. At the 3rd week after transplantin g, in most clones, anthocyanins were detected in the young thick roots that had the potential to develop into storage roots. The pattern of anthocyani n accumulation was characterized into three distinctive phases: (1) an init ial rapid increase during the 3rd to 6th week, (2) no change or a slight de crease during the 6th to 12th week, and (3) a slight increase during the 12 th to 17th week. Northern blot analysis indicated that mRNA levels of dihyd roflavonol 4-reductase (DFR), one of the key enzymes of the anthocyanin bio synthetic pathway, was expressed throughout the stage of storage root devel opment. In addition, DFR mRNA appeared to be the most abundant at the 6th w eek, and reduced at the 9th week, which coincides with the change in anthoc yanin content. These results suggest that anthocyanin is synthesized throug hout the stage of storage root development, but not in a steady manner, and that anthocyanin accumulation in sweet potato could be related to the tran scriptional regulation of anthocyanin biosynthetic genes. The rate of incre ase in anthocyanin content during the 3rd to 6th week was significantly hig her in clones with a high anthocyanin content than in clones with a low ant hocyanin content. It may be possible to screen clones after the 9th week wh en the percentage of peonidin, which is an index for anthocyanin compositio n in purple-fleshed sweet potato, become constant, and the large storage ro ots (more than 20 mm in diameter) are produced in most clones.