Rapid changes in translocation patterns in soybeans following source-sink alterations

The effects of source-sink alterations on the translocation patterns to soybean ("Fiskeby V") pods were studied using a pod leakage technique. The distribution of assimilates from a source leaf using double pulse experiments was followed at the pods at the source node and the node immediately below. Alterations were made by shading, illuminating, or excising two-thirds of the leaf area of the leaf at the node below. In control experiments both pulses exhibited identical time-course patterns at both nodes. Shading the lower leaf during the first half of the experiment and illuminating during the second reduced the distribution of 14C-assimilate to the lower node's pods from the source leaf by approximately 30 to 50% while having no effect at the source node. Illuminating the lower leaf during the first half of the experiment followed by excision of two-thirds of that leaf's area and shading increased the import from the source leaf by 4- to 33-fold relative to the control while reducing the distribution to the source node by up to 40%. The change in distribution pattern took place in less than 30 minutes with no apparent change in the source leaf net photosynthesis or in the rate of movement to the pods. The results indicate that any alterations in the source-sink balance will quickly produce a change in the distribution patterns to the pods.