Plant Physiol. Drug Metab Dispos
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Plant Physiology 71:582-587 (1983)
© 1983 American Society of Plant Biologists

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Articles

Reversible Inactivation of Nitrate Reductase by NADH and the Occurrence of Partially Inactive Enzyme in the Wheat Leaf 1

Arun P. Aryan, Richard G. Batt and William Wallace

Agricultural Biochemistry Department, Waite Agricultural Research Institute, University of Adelaide, Glen Osmond, South Australia 5064, Australia

Nitrate reductase from wheat (Triticum aestivum L. cv Bindawarra) leaves is inactivated by pretreatment with NADH, in the absence of nitrate, a 50% loss of activity occurring in 30 minutes at 25°C with 10 micromolar NADH. Nitrate (50 micromolar) prevented inactivation by 10 micromolar NADH while cyanide (1 micromolar) markedly enhanced the degree of inactivation.

A rapid reactivation of NADH-inactivated nitrate reductase occurred after treatment with 0.3 millimolar ferricyanide or exposure to light (230 milliwatts per square centimeter) plus 20 micromolar flavin adenine dinucleotide. When excess NADH was removed, the enzyme was also reactivated by autoxidation. Nitrate did not influence the rate of reactivation.

Leaf nitrate reductase, from plants grown for 12 days on 1 millimolar nitrate, isolated in the late photoperiod or dark period, was activated by ferricyanide or light treatment. This suggests that, at these times of the day, the nitrate reductase in the leaves of the low nitrate plants is in a partially inactive state (NADH-inactivated). The nitrate reductase from moisture-stressed plants showed a greater degree of activation after light treatment, and inactive enzyme in them was detected earlier in the photoperiod.

1 Supported by a scholarship (A. P. A.) from University of Adelaide Research Grant.






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