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

摘要

When rice seedlings, after the growth for 26 days in water alone, were transferred to nutrient medium contained 1 mM NH4Cl, 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. NH4Cl was effective at concentrations as low as 50μM. A supply of either 1 mM NaNO3or 0.5 mM NH4NO3also caused such increases, but NHa4Cl 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 NH4Cl. Moreover, the mRNA for NADH-GOGAT in rice roots accumulated markedly within 12 h of the start of a supply of NH4Cl. A possible role for the rapid response of NADH-GOGAT to a supply of NH4C1 is discussed