VIEW ARTICLE

Light and Electron Microscopy of Potato Virus M Lesions and Marginal Tissue in Red Kidney Bean. C. Hiruki, Associate Professor, Department of Plant Science, University of Alberta, Edmonton, Canada; J. C. Tu, Former postdoctoral Fellow, Department of Plant Science, University of Alberta, Edmonton, Canada, Present address of junior author: Electron Microscope Laboratory, University of Alberta. Phytopathology 62:77-85. Accepted for publication 2 August 1971. DOI: 10.1094/Phyto-62-77.

Local lesions and marginal tissue in potato virus M (PVM)-infected Phaseolus vulgaris ‘Red Kidney’ bean were studied by light and electron microscopy. Three zones, from the margin toward the central zone of lesions, were represented by non-necrotic cells, “seminecrotic” cells which were discolored but not disintegrated, and necrotic cells. Callose, stained with aniline blue, was detectable by the fluorescent method 3 to 4 days after inoculation, and was deposited in a zone of non-necrotic cells at the lesion margin as the lesions expanded. Thickening, due to callose deposition, was observed on the inner wall of non-necrotic cells immediately adjacent to seminecrotic ones. Such thickening, as determined by electron microscopy, was structurally less complicated than that of seminecrotic cells. Seminecrotic cells surrounding the necrotic zone were characterized initially by roughening of the plasmalemma and accumulation of membrane-bounded vesicles and tubules in the area between the cell walls and the protoplast. Callose deposition formed secondary wall thickening which sealed off the plasmodesmata. It is suggested that these changes in cell wall structure are related to a series of events of localization. The cell-to-cell spread of PVM may be restricted by blocking of plasmodesmata connections initially by deposition of callose and later, more extensive secondary wall thickening involving boundary formation.