Kinetics of C-14 Translocation in Soybean

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Abstract
The kinetics of 14C-assimilates in the soybean leaf were studied in pulse labeling and steady state labeling experiments. 14C-Sucrose apparently served as the ultimate source, at least, of translocated 14C-sucrose. However, since the specific activity of leaf sucrose reached a maximum within 5 minutes after pulse labeling, whereas that of exported sucrose did not reach a maximum until at least 20 minutes, it appeared that there were two sucrose compartments in the leaf. A possible physical basis for the two compartments may be the mesophyll (a photosynthetic compartment) and a specialized “paraveinal mesophyll” (a nonphotosynthetic compartment), through which photosynthate must pass on its way to the veins.