PHOTOREACTIVATION OF DNA-CONTAINING CAULIFLOWER MOSAIC VIRUS AND TOBACCO MOSAIC VIRUS RNA ON DATURA

Abstract— Datura stramonium L. is a local lesion host for TMV-RNA and DNA-containing cauliflower mosaic virus (CAMV). Datura can photorepair UV-damaged TMV-RNA and CAMV, giving photoreac-tivation sectors of 0.40 and 0. 33 , respectively. Dose response curves for photoreactivation of TMV-RNA and CAMV show that 4540 min of cool white light (15 W.m^-2) is required for maximum photoreactivation. Blue light and near UV are equally effective in photoreactivating UV-irradiated TMV-RNA, whereas near UV is initially more effective than blue light for the photorepair of UV-inactivated CAMV. Higher doses of near UV apparently inactivate the CAMV photorepair system. In the case of CAMV, photoreactivating light must be applied immediately after inoculation with the virus. Two to three hours of incubation in the dark after inoculation results in complete loss of response to photoreactivating irradiation. In contrast, limited photoreactivation of TMV-RNA occurs even after 4 h of dark incubation after inoculation, although photoreactivating irradiation is most effective when applied immediately after inoculation. Light is required for the maintenance of photoreactivation for both TMV-RNA and CAMV. Daturas placed in the dark for six days lose their ability to photoreacti-vate. Recovery of the TMV-RNA photorepair system is rapid; complete recovery attained with 90 or more min of white light (15 W m-'). Recovery of CAMV photorepair system is slow; 90% recovery attained after only 20 h of light. However, full recovery can be induced by as little as 6h of light when CAMV is inoculated 24 h after the onset of illumination. These results suggest two photorepair systems are present in Datura .