Time-course Study of Translocation of Products of Photosynthesis in Soybean Plants

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Abstract
About 25% of the Cl4 assimilated by the primary leaves of young soybean plants (Glycine max. var. Comet) during 10 minutes of photosynthesis in Cl4O2 was moved out of the leaf during the next 6 hours. Additional translocation during the following 18 hours raised the export to its maximum of about 35%. During the first 2 hours, most of the translocated Cl4 was in ethanol-soluble products, but between 2 and 6 hours a major part of this was converted to ethanol-insoluble forms in the root, stem and top parts of the plant. The gradient of Cl4 concentration per unit length of stem decreased logarithmically from the input node to the base at all time intervals up to at least 44 hours. Although serine and glycine were the first Cl4-labeled compounds to reach the stem, they were soon replaced by the main output of sucrose-C14. After about 2 hours the sucrose-Cl4 was displaced by a group of compounds which persisted in the stem for the remaining 44 hours. These included asparagine, malic, aspartic and glutamic acids, alanine and the hexoses. While some of these compounds may have arrived in the stem by way of the return flow from the root, it is concluded that most of the C14 translocated to the stem from the primary leaf is rapidly withdrawn from the conducting tissue where it accumulates and is metabolized. The logarithmic gradient of Cl4 in the stem arises from this accumulation.