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Articles

Kinetics of C-14 Translocation in Soybean

III. Theoretical Considerations ¹

^a Department of Biochemistry and Biophysics, Iowa State University, Ames, Iowa

Based largely on data from soybean, some mathematical models are derived to describe the transport kinetics of ¹⁴C-photosynthate. The effects of leaf size, leaf shape, and translocation velocity on the rate of tracer efflux from the leaf are considered, and it is shown that the duration of these effects will approximate the time required for tracer to reach the petiole from the farthest point of the leaf. This duration is designated as the "kinetic size" of the leaf. Although its effect will be slight in the case of soybean (about 2 to 3 minutes), a considerable effect of the kinetic size will be found in the case of large leaves, or when the translocation velocity is low.

Source pool kinetics in soybean are described by a two-compartment model, one compartment representing a photosynthetic compartment and the second (the source pool) a nonphotosynthetic compartment next to the veins. The kinetics in the petiole are approximated by a two-compartment model representing the translocation stream and tissues outside the translocation stream. A combination of the models predicts fairly accurately the translocation kinetics observed in soybean.

The models are compared with others in the literature. Although the assumptions are in substantial agreement with those made by Evans, Ebert, and Moorby, they are inconsistent with the model based on the movement of transcellular strands presented by Canny and Phillips.

¹ This work was supported in part by United States Public Health Service Fellowship 1-F1-GM-22,031, to the author, and in part by National Science Foundation Grant GB-114, to Dr. Sam Aronoff.