Ammonia Regulation of Carbon Metabolism in Photosynthesizing Leaf Discs

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Abstract
Alfalfa (Medicago sativa L. variety 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 indicate that pyruvate kinase was activated by ammonia, resulting in increased transfer of photosynthetically incorporated C to synthesis of amino acid skeletons at the expense of sucrose synthesis. C flow through enzymes catalyzing the anaplerotic reactions was apparently stimulated.