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Articles

Partitioning of ¹⁴C-Photosynthate, and Long Distance Translocation of Amino Acids in Preflowering and Flowering, Nodulated and Nonnodulated Soybeans ¹

^a Department of Agronomy, University of Wisconsin, Madison, Wisconsin 53706

The influence of stage of development (preflowering versus flowering) in nodulated and nonnodulated soybeans (Glycine max [L.] Merr. cv. Wells) on partitioning of ¹⁴C into assimilates following exposure of a soybean leaf to ¹⁴CO₂ by both steady-state and pulse-labeling techniques was studied. Blades on the second fully expanded leaf from the stem apex were exposed to ¹⁴CO₂. Radioactive assimilates were extracted from source leaf blades, petioles, and stems (both the path up and path down from source leaf), were separated into neutral (sugars), basic (amino acids), and acidic (organic acids, sugar phosphates) fractions by ion exchange chromatography. The basic fraction was further resolved using thin layer chromatography and the percentage of radioactivity recovered in each amino acid was determined.

The distribution of radioactivity in the neutral, basic, and acidic fractions of the source leaf blades was significantly different from that of the transport path (petiole and stems). About 70% of the radioactivity in source leaf blades was recovered in the neutral fraction, whereas about 90% of the recovered radioactivity in the path was in the neutral fraction. ¹⁴C-Aminoacids constituted 8 to 17% and 2 to 7% of the recovered radioactivity in source leaves and paths, respectively. Recovered ¹⁴C in organic acids ranged from 13 to 20% and 2 to 7% in source leaves and paths, respectively. Partitioning of ¹⁴C-assimilates among the neutral, basic, and acidic fractions was not affected by the presence of nodules or flowers. However, when steady-state labeling was compared to pulse labeling, a significantly lower percentage of ¹⁴C was recovered in the neutral fraction with a concomitant increase in the basic fraction. Asparagine-arginine, serine, glutamate, -aminobutyrate-alanine, and aspartate accounted for 69 to 85% of the recovered radioactivity in the basic fraction from the various treatments. [¹⁴C]Serine was significantly higher in pulse-labeling experiments, whereas glutamtate and proline were higher with steady-state labeling. [¹⁴C]Serine was significantly higher in nonnodulated plants than in nodulated plants, whereas -aminobutyrate-alanine was significantly higher in preflowering plants as compared to flowering plants.

³ Present address: Department of Agronomy, Cornell University, Ithaca, New York 14853.

⁴ Present address: Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, Minnesota 55101.

¹ Research supported by College of Agricultural and Life Sciences, University of Wisconsin, Madison; the Department of Agronomy, Purdue University, Agricultural Experiment Station, West Lafayette, Indiana; the National Soybean Crop Improvement Council, USDA-CSRS Grant 616-15-72; and the American Soybean Association Research Foundation Grant 75-ASARF-208-3. Journal Paper 7256, Purdue University.