Abstract
The rate of photosynthesis decreases when total non-structural carbohydrate (TNC) increases in the leaves. Glucose accumulation may inhibit the expression of genes for photosynthetic components and thereby reduce the photosynthetic activity. It is hypothesized that the effect of sugar accumulation on photosynthesis changes with leaf development, because the roles of TNC differ in leaf age. To examine this hypothesis, we supplied sucrose solution to the roots of bean plants for 5 days at various developmental stages of the primary leaves, and measured photosynthetic properties.
The TNC in the sucrose-treated leaves were about twice of those in the control leaves. The photosynthetic rate was independent of the sucrose treatment at early developmental stages. However, the photosynthetic rate of sucrose-treated leaves decreased more rapidly than that of control leaves with leaf age. These results suggest that the sugar repression of photosynthesis occurs in the source leaves but not in the sink leaves.
