Abstract
Leaves of bright tobacco NC 95 infected with tobacco vein mottling virus (TVMV) and tobacco mosaic virus (TMV) were fractionated into subcellular fractions for protein quantitation and enzyme assay. Both viruses increased soluble proteins in the nuclear, chloroplastic and ribosomal fractions, whereas TMV infection lowered cytoplasmic protein content. Leaves infected with TVMV significantly increased total soluble proteins. Virus infection enhanced peroxidase activity in the cytoplasm but decreased activity in the chloroplastic and mitochondrial fractions. Polyphenol-oxidase concentrated in the chloroplast and its activity were not altered by virus infection. Ribosomal fraction was rich in protease in both virus-infected leaves. In the chloroplasts, protease increased in activity in the TMV-infected leaves but maintained a level as low as the control in leaves showing TVMV symptom. The accumulation of soluble proteins in the TVMV-infected leaves is possibly, in part, attributed to a low concentration of protease.