Immunogold Localization of Parsnip Yellow Fleck Virus Particle Antigen in Thin Sections of Plant Cells

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Abstract
The distribution of parsnip yellow fleck virus particle antigen in infected cells of Nicotiana clevelandii or Spinacia oleracea was examined by immunogold labelling of ultrathin sections. Best results were obtained by pretreating sections with Decon 75 followed by long incubation times on antiserum (16 h) and gold probe (6 h). The cytoplasmic inclusions induced by infection have three main components: accumulations of 20 to 30 nm diameter tubules, granular bodies and amorphous matrix material. Much gold label was located over the area of amorphous matrix material whereas the other components of the inclusions were not labelled. Specific but less dense labelling was observed over virus-induced cell wall outgrowths, and over other areas of cell wall and some nuclei in infected cells. Virus-like particles found in 45 nm diameter tubules within the cell wall outgrowths were not labelled, perhaps because they were inaccessible to the antibody. The results indicate that large amounts of virus particle antigen are present in cells. However, the number of recognizable virus particles was considerably less than expected from the amount of virus extracted from leaves.