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Source Pool Kinetics for ¹⁴C-Photosynthate Translocation in Morning Glory and Soybean ^1,2

Department of Botany, University of Georgia, Athens, Georgia 30602

The kinetic behavior of translocation profiles indicates that their shape is determined largely by the rate at which tracer enters the sieve tubes in the source leaf. Confirmation of this relationship was sought by investigating the kinetics of ¹⁴C in the immediate source pool for translocated sucrose in soybean (Glycine max L., cv. Bragg) and morning glory (Ipomea nil Roth, cv. Scarlet O'Hara) leaves. Quantitative microautoradiography was used to follow the water-soluble ¹⁴C contents of the companion cells in minor veins after pulse-labeling with ¹⁴CO₂. In both morning glory and soybean, the observed kinetics in the companion cells matched reasonably well those expected from the shape of the translocation profiles.

Marked compartmentation of sucrose was evident in soybean leaves in that the specific radioactivity of total leaf sucrose was greatest immediately after labeling and quickly declined, whereas labeling in the companion cells was low at first and did not reach a maximum for about 35 minutes. In morning glory leaves, the kinetics of sucrose specific radioactivity and of companion cell-labeling more closely paralleled one another.

⁴ Present address: Department of Agronomy, Purdue University, West Lafayette, Indiana 47907.

⁵ Present address: Monsanto Co., Agricultural Research Dept. T1G, 800 N. Lindbergh Blvd., St. Louis, Missouri 63166.

¹ This work was supported by National Science Foundation Grants GB33905 and PCM75-09357 to D. B. F.

² Portions of this work were presented at the NATO Advanced Studies Institute on Phloem Transport, held in Banff, Alberta, Canada in 1974.

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