Effects of ultraviolet radiation on infection by intact and phenol-disrupted red clover mottle virus.

Abstract

Abstract Exposing French bean leaves to ultraviolet radiation after inoculation with red clover mottle virus decreased numbers of infections more than did exposure before inoculation. The decrease produced by a given dose of radiation differed with plants in different physiological states. Treatments that increased susceptibility to infection also increased the effects of the radiation. Irradiation before inoculation affected lesion numbers similarly whether the inoculum was intact or phenol-disrupted virus provided the leaves were in the dark after irradiation, but when leaves were in the light effects were much greater with disrupted virus. Intact virus is apparently better able than disrupted virus to survive while light restores the capacity of leaves to support infection. The effects of photoreactivation depended on the radiation dose; leaves given small doses befor inoculation and then exposed to visible light produced more lesions than the controls when the inoculum was intact virus, but usually fewer when it was disrupted virus. Irradiation immediately after inoculation decreased lesions more with disrupted virus than with intact virus, but infection centers initiated by disrupted virus increased their resistance sooner and more rapidly. Infection centers initiated by intact virus retained their original susceptibility for about 2 hours at 24–28° and 6–8 hours at 16°. At 32° resistance did not increase even after 22 hours; plants placed at 24° after 22 hours at 32° produced about half as many lesions as those kept at 24° continuously after inoculation. At 32°, infection centers initiated by disrupted virus also failed to increase their resistance to inactivation by the radiation, and few survived 4 hours, even in unirradiated leaves. Hence, whatever may happen at lower temperatures, intact virus seems not to dissociate into protein and nucleic acid in leaves at 32°.