THE INTESTINE IS A SITE OF PASSAGE FOR POTATO LEAFROLL VIRUS FROM THEGUT LUMEN INTO THE HAEMOCOEL IN THE APHID VECTOR, MYZUS-PERSICAE SULZ

Four detection techniques, three of which gave reliable identification of the virus particles, were used to locate potato leafroll virus (PL RV) in the alimentary canal of its main aphid vector, Myzus persicae S ulz: immunofluorescence on cryostat sections, conventional transmissio n electron microscopy on ultrathin sections and immune electron micros copy with gold labeling, either prior to or after fixation-embedding. Each method clearly showed the presence of the virus in the intestine epithelium and its absence in cells of the other parts of the alimenta ry canal. Under the experimental conditions used, the intestinal cells seemed to be the pathway for PLRV transport from the gut lumen into t he haemocoel. Electron microscopy examinations showed many virus parti cles close to the apical plasmalemma of the epithelial cells in the gu t lumen of the intestine. Other particles were seen in shallow pit-lik e regions or surrounded by coated vesicles in the apical part of these cells. Thus the virus particles seemed to enter the epithelial cells of the intestine by a mechanism of endocytosis. In the cytoplasm of th ese cells, virions were also frequently observed in isolated - or more often aggregated - tubular vesicles. The latter could be involved in PLRV transport through the cell since they were observed fusing with d ifferent cell organelles. A few viral particles were also detected in lysosomes as well as in multivesicular bodies. Virus particles were ob served between the plasmalemma and basal lamina of the intestine cells but not in the haemocoel, where probably they were quickly dispersed. Our results are discussed in relation to other reports which have sho wn hindgut and stomach as sites of passage from the gut lumen into the aphid's body cavity for PLRV and other circulative viruses.