THE ISOLATION OF DEFECTIVE TOBACCO MOSAIC VIRUS STRAINS

Abstract

Two strains of TMV, PM1, and PM2, which are defective in their capacity to induce the formation of complete virus particles have been isolated. The infective principle behaves in a manner similar to that of infectious nucleic acid isolated from ordinary strains of TMV both in its instability and in its manner of fractionation from leaf homogenates. The strain PM1 apparently has lost the capacity to induce the formation of a protein which would appear similar to virus protein by our methods of analysis. The PM2 strain does induce the formation of such a protein, but why complete virus is not formed in the host tissue remains a problem for further investigation. Possibly "proteinless" viruses can spread in the host plant only from cell to cell, probably through the plasmodesmata, and either are incapable of entering or are rapidly inactivated in the conducting elements of the vascular system. These peculiar strains of TMV may prove useful as a model system for study of infection induced by "proteinless" virus. It should be noted that there is no viral antigen associated with the infectious entity. The consequences of this feature for animal virus infection might be quite drastic because the infective agent would be immune to antibody neutralization.