Light Quality and Photoreactivation of Plants and Viruses

Visible light of different spectral regions was tested for its ability to reverse three effects of ultra‐violet radiation, namely, injury (glazing) of French bean leaves, increased resistance of French bean leaves to infection by the Rothamsted tobacco necrosis virus, and inactivation of potato virus X. The different spectral regions were obtained with colorimetric filters and the filtered and unfiltered light from fluorescent tubes; all three effects were reversed only by regions of wave‐lengths shorter than 4700 Å. Thirty minutes of illumination at 300–380 f.c. gave substantial photo‐reactivation, but irradiated potato virus X did not become affected by visible light until 30 min. after tobacco leaves were inoculated.