Effects of two strains of tobacco mosaic virus on growth and RNA content of tobacco leaves

Abstract

Tobacco leaves 1.5 to 18 cm long were infected with tobacco mosaic virus (TMV) strains vulgare or flavum. Nucleic acids were extracted, and fractionated and assayed by gel electrophoresis. Leaf growth and contents of DNA, ribosomal RNA, chloroplast ribosomal RNA, transfer RNA, and TMV-RNA were measured at various times after infection. The younger the leaf infected, the longer the duration of synthesis of TMV-RNA, and the higher the final virus concentration reached. Synthesis of flavum-RNA was as great as that of vulgare-RNA in young leaves, but was much less than that of vulgare-RNA in old leaves. The growing, healthy leaf accumulated ribosomal RNA, chloroplast ribosomal RNA, and transfer RNA. The maximum contents of these per leaf were reached as or just before the leaf reached its maximum length of 15–20 cm. Thereafter there was a loss of these components. TMV-infection of a 1.5 cm-long leaf inhibited its growth and nucleic acid accumulation. Infection of a 5 cm-long leaf had no effect on the subsequent rises in ribosomal RNA and transfer RNA contents, but chloroplast ribosomal RNA accumulation was inhibited. The effects of TMV-strains vulgare and flavum on young leaves were similar. Infection of older leaves, at or later than the time of maximum ribosomal RNA content, led to contents of ribosomal and transfer RNA higher than in control leaves, as the rate of loss of these two components was reduced, especially by strain flavum. Under no conditions was a degradation of cytoplasmic ribosomal RNA found as a result of viral infection, but chloroplast ribosomal RNA was quickly degraded in flavum-infected leaves.