Effect of glutamine supply on nitrate reductase isoforms in maize seedlings
1998
Shankar, N. | Srivastava, H.S.
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 seedlings inhibited NADH: NR activity in light, but increased the same in darkness. NADPH:NR in roots and scutella however, was inhibited by the amide both in light and in darkness, the inhibition in light being higher than that of NADH:NR under similar conditions. The in vitro provision of glutamine to the enzyme preparation from light grown roots had no effect, but Mg2+ or ATP inhibited NADH:NR activity, both in the absence as well as presence of glutamine. The nitrate content of the excised organs was little affected by glutamine supply but for a substantial decline in roots in light. Nitrite content on the other hand, was increased substantially in all tissues and in both light and darkness. The uptake of nitrate by intact seedlings was inhibited by glutamine. The total protein content of excised organs was unaffected by glutamine supply in dark but in light it declined in scutellum at higher concentrations of the amide and increased at lower concentrations and at each 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.
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