Ferricyanide restores nitrate reductase activity in leaf extracts of water stressed wheat seedlings

Nitrate reductase (EC 1.6.6.1) activity declined rapidly in leaves of wheat seedlings following polyethylene glycol-induced water stress. The decrease in NADH-nitrate reductase was accompanied by a concomitant loss of FMNH2- and reduced benzyl viologen-linked nitrate reductase activities. Incubation of dialysed leaf extracts with potassium ferricyanide restored the enzyme activity almost to the same level as that in non-stressed plants. The decline in nitrate reductase, at least during the initial stages of water stress, hence seems to be primarily due to redox-mediated inactivation rather than diminished synthesis of the enzyme.