Tobacco rosette disease: An ultra-structural study

Abstract Electron microscopy of tobacco leaves infected with the rosette disease revealed isometric virus particles of about 25 nm dia. in the phloem cells of the vein distortion areas. Vesicles with granular and fibrillar networks, enclosed singly or in groups within a second membrane, occurred in the cytoplasm as well as in the distended portions of the nuclear envelope and in almost empty sieve tubes. Tubular structures were present in parenchymatic phloem cells mixed with the isometric virus particles, containing cytoplasm vacuoles in the chloroplasts of the mesophyll and epiderm in an advanced stage of infection. The ultra-structural changes are discussed in relation to a proposal that the virus observed might belong to the luteoviruses and be one of the two viral components of the disease.