Ultrastructural changes in leaf cells of poplar naturally infected with poplar mosaic virus

In poplar (Populus x euramericana cv. Robusta) infected with poplar mosaic virus, rod-shaped, virus-like particles (c. 13 nm in diameter) occurred singly or in loose bundles in the cytoplasm of cells in palisade and mesophyll tissue and in vascular parenchyma. The cell walls had local overgrowths consisting of membranous elements (vesicles and/or tubules) in a loosely fibrillar matrix. Accumulations of endoplasmic reticulum with enlarged cisternae occurred near cell nuclei. We are indebted to Mr A. G. Mackay, Bryant and May (Forestry Ltd) for supplying the poplar material and we acknowledge technical assistance from Mrs D. McCall. The work was supported financially by the Natural Environment Research Council.