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Ammonia Regulation of Carbon Metabolism in Photosynthesizing Leaf Discs ¹

Zvi Plaut^b,3 and James A. Bassham^b

^a Western Regional Research Center, Agricultural Research Service, United States Department of Agriculture, Berkeley, California 94710, ^b Laboratory of Chemical Biodynamics, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720

Alfalfa (Medicago sativa L., var. El Unico) leaf discs, floating on buffer containing NH₄Cl and photosynthesizing with ¹⁴CO₂, produced more labeled amino acid and less sucrose than did control discs (no added NH₄Cl). The level of pyruvate increased and that of phosphoenolpyruvate decreased. These and other changes in levels of labeled compounds led us to conclude that pyruvate kinase was activated by ammonia, resulting in increased transfer of photosynthetically incorporated carbon to synthesis of amino acid skeletons at the expense of sucrose synthesis. Carbon flow through enzymes catalyzing the anaplerotic reactions was apparently stimulated.

³ Present address: Agricultural Research Organization, Bet-Dagan, Israel.

¹ This work was carried out at the Laboratory of Chemical Biodynamics, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720. It was supported in part by the Division of Biomedical and Environmental Research of the U.S. Energy Research and Development Administration, and in part by the U.S. Department of Agriculture.

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