Electron microscopy of crystalline inclusions of tobacco mosaic virus in leaf tissue.

Abstract

By use of short fixation in potassium permanganate, it has been possible to demonstrate the internal organization of crystalline TMV inclusions in leaf and epidermal hair cells of tobacco plants. Virus particles first are seen in the ground cytoplasm of infected cells as small aggregates of parallel rods with ends aligned. These aggregates increase in size and become monolayers and three-dimensional crystals. Monolayers are formed most abundantly in the apical cells of epidermal hairs. They consist of plates of parallel particles, the length of one particle in thickness, with particle ends aligned, and are variable in length and width. Three-dimensional crystals (hexagonal crystals) are formed in the cytoplasm of vacuolate cells and are composed of several to many parallel monolayers joined into a single crystal. Paracrystals (“needle crystals,” spindlelike inclusions) are elongate, and are made up of linear aggregates of virus particles united end to end. The virus particles, in monolayers, in three-dimensional crystals, and in paracrystals, appear to be arranged with hexagonal two-dimensional regularity at right angles to their lengths. Observations on paracrystalline inclusions suggest that these may be secondary aggregation products of the breakdown of crystalline aggregates.