VIRUS PARTICLES IN CHLOROPLASTS OF PLANTS INFECTED WITH U5 STRAIN OF TOBACCO MOSAIC VIRUS

Electron microscopy revealed clusters of tubular particles in most of the chloroplasts in Turkish tobacco leaves infected with the U5 strain of tobacco mosaic virus. The tubular morphology corresponded to that of the axial coil of RNA in virions of TMV. Labeling experiments with ferritin antibodies indicated the presence of a capsid of viral protein around the clearly stained RNA. When chloroplasts were extracted from plants infected with U5-TMV and induced to swell in a hypotonic medium, their loss of virions as seen with the electron microscope was correlated with an increase in the infectivity of the ambient medium. No equivalent clusters of virions were seen in chloroplasts of plants infected with the U1 strain of TMV. The infectivity recovered from subcellular fractions composed predominantly of chloroplasts was markedly higher from plants infected with U5-TMV than from plants infected with U1-TMV. © 1968.