Activation of nitrate reductase by extracts from corn scutella

NADH-nitrate reductase (NR) from the primary leaves and root tips of corn seedlings (var. W64A x W182E) were activated by extracts from corn scutella. The activator extracted in potassium phosphate buffer (pH 7.5) or 80% (v/v) ethanol and fractionated by Dowex 1 (acetate) and Dowex 50 (H(+)) resins was recovered in the cationic fraction. The activator was not detected in extracts from shoots, roots, or endosperm of the seedlings. It activated the nitrate-induced cytochrome c reductase of NR complex but had slight inhibitory effects on the activities of FMNH(2)-NR and reduced methylviologen-NR. In addition the activator inhibited the activities of purified NR-inactivating proteins from corn roots (var. Wf9 x 38-11) and rice cell cultures.