A Supply of Nitrogen Causes Increase in the Level of NADH-Dependent Glutamate Synthase Protein and in the Activity of the Enzyme in Roots of Rice Seedlings : GROWTH AND DEVELOPMENT : PROTEINS, ENZYMES AND METABOLISM

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When rice seedlings, after the growth for 26 days in water alone, were transferred to nutrient medium contained 1 mM NH_4Cl, the level of NADH-dependent glutamate synthase (GOGAT) protein and the activity of the enzyme increased more than 10-fold in root, but not in shoots. Both the level of the protein and the activity reached a maximum within 24 h. NH_4Cl was effective at concentrations as low as 50μM. A supply of either 1 mM NaNO_3 or 0.5 mM NH_4NO_3 also caused such increases, but NH_4Cl was most effective. A supply of glutamine or glutamate was less effective. The increase was specific to NADH-GOGAT and little change was observed in the levels of ferredoxin-GOGAT and glutamine synthetase isoproteins in roots. These inducible increases in the levels of NADH-GOGAT protein and in its activity were greater in the root-tip region than at the base of the root. Both 6-methylpurine and cycloheximide completely inhibited the effects of NH_4Cl. Moreover, the mRNA for NADH-GOGAT in rice roots accumulated markedly within 12 h of the start of a supply of NH_4Cl. A possible role for the rapid response of NADH-GOGAT to a supply of NH_4Cl is discussed.
日本植物生理学会の論文