Rapid Changes in Translocation Patterns in Soybeans following Source-Sink Alterations

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Abstract
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 2/3 of the leaf area of the leaf at the node below. In control experiemnts both pulses exhibited identical time-course patterns at both nodes. Shading the lower leaf during the 1st half of the experiment and illuminating during the 2nd reduced the distribution of 14C-assimilate to the lower node''s pods from the source leaf by approximately 30-50% while having no effect at the source node. Illuminating the lower leaf during the 1st half of the experiment followed by excision of 2/3 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 < 30 minutes with no apparent change in the source leaf net photosynthesis or in the rate of movement to the pods. Any alterations in the source-sink balance may quickly produce a change in the distribution patterns to the pods.