1Central Potato Research Institute, Shimla, 171 001, (Himachal Pradesh).
2Himachal Pradesh University, Shimla, 171 005, (Himachal Pradesh).
3Institut de rescherche en biologie vegetale, Universite de Montreal, Montreal, Canada, H1X 2B2.
Potato plants grown under tuber inducing and non-inducing conditions were used to study the activities of invertases, sucrose synthase and carbohydrate status in developing potato leaves. Plants grown under non-inducing conditions continued to grow vegetatively and there was starch accumulation in the leaves, and roots. However, under tuber-inducing conditions, vegetative growth slowed down considerably and there was very little starch accumulation in the leaves and roots, indicating that developing tubers acted as strong sinks for photoassimilates. Invertases were the major enzymes acting on the imported sucrose in the young leaves while sucrose synthase was of minor importance. Of the invertases, cell wall invertase activity was 44–110% higher than the soluble invertase in young leaves, indicating apoplastic unloading of imported sucrose as the major route. Reduced growth and leaf expansion under tuber inducing conditions was supported by 27% reduction in the activity of cell wall invertase. As the leaves developed to become net exporters of carbohydrates, the activity of sucrose degrading enzymes declined by 90%.
