Sink-source interactions: accumulation of sucrose in the apoplast and symplast of the source leaves as a result of sink strength reduction in Pisum sativum L.

The effect of sink-strength-reduction on the carbohydrate content in apoplast and symplast of source leaves was examined in Pisum sativum L. Sink strength was reduced by removing developing seeds or by means of the ‘open seed coat technique’. After seed removal, an increase in the sucrose content could be observed, especially in the apoplast. Starch content did not change during the course of the experiments. Fixation of 14C02 was not influenced by sink-strengthreduction. The increase in the sucrose content can be explained as a consequence of a change in the balance between production and export of sucrose in the source leaves. Reduction in phloem loading may have caused an increase in sucrose content in the leaf apoplast, followed by an increase in sucrose in the leaf symplast, without a change in photosynthesis.