Abstract
Using immunogold cytochemistry, plasmodesmata have been identified as subcellular locations of the protein product (P1) of cauliflower mosaic virus gene 1 in infected turnip tissue. Thin sections, from tissue adjacent to chlorotic local lesions on systemically infected fully expanded leaves, were probed with antiserum to a protein product derived from a lacZ-gene 1 fusion, and with control sera. Modified plasmodesmata between infected mesophyll cells, and plasmodesmata in the end walls of phloem parenchyma cells were specifically labelled with anti-P1 serum. In the former case, the position of the label suggested that P1 was extracellular and had formed a structural component of the modified plasmodesmata. Cell walls at the corners of cells in both healthy and infected tissue were also labelled. Anti-P1 serum also reacted with nuclei and the leaf cuticle, in both healthy and infected tissue. These observations provide strong circumstantial evidence that P1 is involved in the cell-to-cell movement of cauliflower mosaic virus.