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

Thomas L. Housley, Larry E. Schrader, Marna Miller and Timothy L. Setter
Plant Physiology
Vol. 64, No. 1 (Jul., 1979), pp. 94-98
Stable URL: http://www.jstor.org/stable/4265846
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Partitioning of 14C-Photosynthate, and Long Distance Translocation of Amino Acids in Preflowering and Flowering, Nodulated and Nonnodulated Soybeans
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Abstract

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-Amino-acids 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, γ-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 γ-aminobutyrate-alanine was significantly higher in preflowering plants as compared to flowering plants.

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