Nucleic acid and protein synthesis associated with the induction of nitrate reductase activity in radish cotyledons.

1. RNA and protein synthesis was studied during the incubation of excised radish cotyledons in nitrate, conditions that induced nitrate reductase activity in the tissue. 2. Synthesis of total RNA and protein, as measured by the incorporation of radioactive precursor, was significantly stimulated in the presence of nitrate (compared with chloride control), but was decreased in the presence of ammonium nitrate, which induced higher enzyme activity. 3. Synthesis of RNA and protein was required for induction of enzyme activity, as determined by using the inhibitors actinomycin D, puromycin and cycloheximide. 4. On the basis of 5-fluorouracil inhibition, the synthesis of only DNA-like RNA was required for induction, but no differences, either quantitative or qualitative, were observed in DNA-like RNA synthesis in the presence or absence of induction. 5. A 100-fold purification of the nitrate reductase activity showed no increase in nitrate reductase protein, nor any increased incorporation of radioactive precursor into nitrate reductase protein in the induced versus the control system. Such results suggested that the protein synthesis required for induction may be for a protein other than nitrate reductase.