Amino acid metabolism in plant leaf

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Abstract
Recent studies have shown that the incorporation of ammonium nitrogen into amino acids in the leaves is strictly dependent on light (1-4). It is speculated that the effect of light on ammonium assimilation may be through the synthesis of the precursors of amino acids, or by the supply of the energy required for amination and amidation with organic acids. In the Vicia faba chloroplasts Givan et al. (1) exhibited that the synthesis of glutamic acid from a-ketoglutarate was linked with the generation of reduced pyridin nucleotide by photosynthetic electron transport. Mitchell and Stocking (2) suggested the direct coupling of glutamine formation with photophosphorylation in the pea chloroplasts. On the other hand. the processes of nitrate assimilation are more indebted to light than those of ammonium assimilation, because the former ones involve the reduction of nitrate to ammonium which is believed to be light-dependent (5). Canvin and Atkins (6). and Atkins and Canvin (7) reported that the incorporation of 15N-labeled ammonium and nitrate into amino acid fractiom was depressed by the dark treatment and by photosystem inhibitors; 3-(3′,4′-dichlrophenyl)-1-1-dimethylurea (DCMU) and carbonyl-cyanide-m-chlorophenyl-hydrazone(CCCP).