The Role of Light and Nitrate in the Induction of Nitrate Reductase in Radish Cotyledons and Maize Seedlings

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Abstract
The effect of substrate (nitrate), light, temperature and inhibitors of protein synthesis on the induction of nitrate reductase in radish (Raphanus sativus var. Cherry Belle) cotyledons and corn (Zea mays var. Hy2 x Oh7) seedlings was studied. Induction was dependent upon the presence of nitrate in the tissue; neither nitrite nor ammonia would induce the enzyme. The presence of ammonia did not inhibit the induction. Induction was roughly proportional to the amount of nitrate present in the tissue. A higher nitrate content in the induction medium was required for radish than for corn. This difference is attributable to differential rates of uptake. Although illumination during induction caused enhanced induction of enzyme, the role of light is indirect and the effect of light is attributable to enhanced nitrate uptake as a result of increased permeability of the tissue. Induction is temperature-dependent, and maximum induction temperatures were 31[degree]and 38[degree] for radish and corn, respectively. Inhibition of induction of nitrate reductase by actinomycin D, chloramphenicol, and puromycin provides evidence that de novo synthesis is involved.