Photoreactivation of nitrate reductase production in Nicotiana tabacum var. Xanthi.

Ultraviolet (254 nm) irradiation of liquid-cultured tobacco cells inhibited the production of nitrate reductase; subsequent illumination with white light allowed a partial restoration of the synthesis of the enzyme (photoreactivation). Ultraviolet irradiation of these same cells also inhibited their ability to incorporate labeled uridine and labeled amino acids. Subsequent illumination with white light gave a partial restoration of the ability of the cells to incorporate uridine while a similar post-ultraviolet-irradiation treatment failed to restore the amino acid incorporation. The system in tobacco known to repair ultraviolet-damaged viral RNA thus does not seem to repair ultraviolet damage to the protein-synthesizing system of the cell. The photoreactivation of nitrate reductase production is best explained by the action of a DNA photorepairing system.