Nucleolar and cytoplasmic uridine 3H incorporation in virus-infected plants virus-infected plants

Abstract

A marked difference was found in the site of virus-directed uridine- 3H incorporation in Vicia faba root tips infected with broad bean mottle virus (20 mμ sphere; BBMV) and clover yellow mosaic virus (flexuous rod). These comparisons were made with light microscope autoradiography and grain counts and electron microscope autoradiography. Actinomycin D (AMD) was used to inhibit normal RNA synthesis. As reported previously, clover yellow mosaic virus-infected cells showed a striking and highly localized incorporation of uridine- 3H in the nucleoli. Broad bean mottle virus infections, however, showed no such nucleolar incorporation. Grain counts over nucleoli of healthy or BBMV-infected cells showed no significant differences whether AMD was used or not. There was a significantly greater cytoplasmic incorporation of uridine- 3 in BBMV-infected cells than in healthy cells. Electron microscope autoradiograms of BBMV-infected cells often showed incorporation in Golgi zones and endoplasmic reticulum. This was seen only rarely in healthy cells. In addition, clusters of grains appeared frequently in the BBMV-infected cells whereas in healthy cells they were seen primarily as individual grains. It is concluded that different viruses trigger different sites in cells to produce some form of virus-dependent RNA. Preliminary studies with tomato ringspot virus and tomato spotted wilt virus gave results similar to those seen with BBMV.