Some effects of photosensitizing dyes on three plant viruses

Abstract

In light the number of lesions of tobacco mosaic virus (TMV), cucumber mosaic virus (CMV), and alfalfa mosaic virus (AMV) developing in the presence of 1:10,000 neutral red was reduced to 43–65% of the control without dye, depending on the virus involved. No reduction occurred with the dye in the dark. At a higher dye concentration, the number of TMV lesions was reduced in the dark. Photosensitized inhibition of TMV became maximal 4 hours after infection and persisted at that level for at least 16 hours. Infectivity and total virus content curves of TMV grown in Havana 38 tobacco in the presence of neutral red and light had about the same slope. A differential response of the three viruses to photosensitization in vitro was noted. Infectivity of TMV and CMV incubated for 30 minutes with 1:50 neutral red was not changed significantly, whereas infectivity of AMV was greatly reduced. Inhibition of TMV in vitro, however, was achieved by fixing virus preparations in methanol prior to staining. Infectious ribonucleic acid (RNA) of TMV, CMV, and AMV was readily inactivated in the presence of 1:50 neutral red. These results, and those obtained with acridine orange staining of TMV in vivo and in vitro, point to viral RNA as the site of the inhibitory action of dyes.