Abstract
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 transplanting, in most clones, anthocyanins were detected in the young thick roots that had the potential to develop into storage roots. The pattern of anthocyanin accumulation was characterized into three distinctive phases: (1) an initial rapid increase during the 3rd to 6th week, (2) no change or a slight decrease during the 6th to 12th week, and (3) a slight increase during the 12th to 17th week. Northern blot analysis indicated that mRNA levels of dihydroflavonol 4-reductase (DFR), one of the key enzymes of the anthocyanin biosynthetic pathway, was expressed throughout the stage of storage root development. In addition, DFR mRNA appeared to be the most abundant at the 6th week, and reduced an the 9th week, which coincides with the change in anthocyanin content. These results suggest that anthocyanin is synthesized throughout the stage of storage root development, but not in a steady manner, and that anthocyanin accumulation in sweet potato could be related to the transcriptional regulation of anthocyanin biosynthetic genes. The rate of increase in anthocyanin content during the 3rd to 6th week was significantly higher in clones with a high anthocyanin content than in clones with a low anthocyanin content. It may be possible to screen clones after the 9th week when the percentage of peonidin, which is an index for anthocyanin composition in purple-fleshed sweet potato, become constant, and the large storage roots (more than 20 mm in diameter) are produced in most clones.
