Indian cassava mosaic virus: ultrastructure of infected cells

Ultrastructural examination of leaf tissue of Nicotiana benthamiana infected with Indian cassava mosaic virus (ICMV) revealed abnormalities in phloem and, occasionally, xylem cells. Nuclei contained granular inclusion bodies which seemed to be largely composed of virus-like particles and were shown by immunogold labelling (IGL) to be rich in ICMV coat protein. Later in infection, hollow spheres made up of fibrillar material were produced. Virus coat protein was not a necessary component of these structures but was sometimes found in their hollow centres. Cytoplasmic abnormalities were uncommon but a few vascular parenchyma cells contained paracrystalline aggregates which seemed to be made up of hollow tubes 30 to 40 nm in diameter. Some of these same cells also had large areas of cytoplasm which contained numerous randomly orientated tubules about 20 nm in diameter. No ICMV coat protein could be detected by IGL in either the paracrystalline or the tubule-containing inclusions. The ultrastructural effects of ICMV resemble those of other whitefly-transmitted geminiviruses, but with some differences of detail, and they also include types of abnormality not previously recorded.