EFFECT OF GLUTAMINE SUPPLY ON NITRATE REDUCTASE ISOFORMS IN MAIZE SEEDLINGS

Supply of 1 to 20 mM glutamine in the presence of 5 mM nitrate to the detached roots, scutella or shoots for 24 h from 5-day-old maize seedl ings inhibited NADH:NR activity in light, but increased the same in da rkness. NADPH:NR in roots and scutella however, was inhibited by the a mide both in light and in darkness, the inhibition in light being high er than that of NADH:NR under similar conditions. The in vitro provisi on of glutamine to the enzyme preparation from light grown roots had n o effect, but Mg2+ or ATP inhibited NADH:NR activity, both in the abse nce as well as presence of glutamine. The nitrate content of the excis ed organs was little affected by glutamine supply but for a substantia l decline in roots in light. Nitrite content on the other hand, was in creased substantially in all tissues and in both light and darkness. T he uptake of nitrate by intact seedlings was inhibited by glutamine. T he total protein content of excised organs was unaffected by glutamine supply in dark but in light it declined in scutellum at higher concen trations of the amide and increased at lower concentrations and at eac h concentration in the shoots. The experiments demonstrate that NADPH: NR is more sensitive to glutamine than the NADH:NR and that the amide has a plurality of effects on nitrate uptake and assimilation process. (C) 1998 Elsevier Science Ltd. All rights reserved.