GRAPEVINE FANLEAF NEPOVIRUS P38 PUTATIVE MOVEMENT PROTEIN IS LOCATED ON TUBULES IN-VIVO

In Chenopodium quinoa cells infected with grapevine fanleaf virus, tub ular structures are formed which protrude from or penetrate the cell w all and which contain virus-like particles. These structures are thoug ht to be involved in cell-to-cell spread of the virus. Immunogold cyto chemistry using immunoaffinity-purified antibodies permitted the locat ion of the P38 putative movement protein: of grapevine fanleaf virus ( GFLV) in or on these tubular structures. We have shown by light and el ectron microscopy that similar structures are formed at the surface of C. quinoa protoplasts, in the absence of cell wall and consequently o f plasmodesmata. These tubules, although not abundant, measured 40 to 60 nm in diameter and up to 30 mu m in length. By immunofluorescence a nd immunogold-silver staining, P38 was localized along these structure s, Together with P38 involvement in tubule formation in planta, this s upports the idea that P38 protein has a role in the cell-to-cell sprea d of GFLV. These studies also revealed that P38 is very abundant in th e cytoplasm of infected protoplasts. This subcellular location, althou gh unusual for a movement protein, is, however, in agreement with prev ious subcellular fractionation experiments with P38 protein in C. quin oa plants.