Effects of exogenous injection of different sugars on leaf photosynthesis,dry matter production and adenosine 5 '-diphosphate glucose pyrophosphorylase (AGPase) activity in sweet potato, Ipomoea batatas (Lam.)

Solutions of sucrose, glucose and fructose were artificially injected into the stems of sweet potato plants. The effects of solution injection on both dry matter production and the activity of adenosine 5'-diphosphate glucose pyrophosphorylase (AGPase) in tuberous roots were investigated and compare d. The total weight of carbon (Tc) artificially and photosynthetically supp lied to a plant during the treatment period of 40 days was 0.987-1.869 time s the weight of photosynthetically assimilated carbon alone. At the final s ampling time, the dry matter weight of tuberous roots in the plants injecte d with sugar solutions showed a 2.73-9.13-fold increase over that of the co ntrol plant. The root weight linearly increased with Tc. The activity of AG Pase was also enhanced by solution injections, with 27-63 % increases compa red to the control, but was not significantly related to Tc The injection o f sugar solutions is concluded to have a dual effect on root production in sweet potato. One effect is that the increased sugar concentration in the p lant increases AGPase and sink activities, and the other effect is that the increased carbon supply quantitatively promotes starch synthesis and accum ulation in roots.