Three Dimensional Reconstruction of Tobacco Mosaic Virus Induced Structural Changes in Nicotiana tabacum

Infection of Nicotiana tabacum by Tobacco mosaic virus (TMV) induces severe ultrastructural changes in leaves such as the accumulation of virions in the cytosol. Even though these changes have been investigated in detail on the two dimensional level, three dimensional (3D) changes induced by TMV-infection remained unclear. This study was aimed to investigate 3D changes during TMV-infection in leaves and to correlate such changes with fine structural changes in chloroplasts by transmission electron microscopy (TEM) and image analysis. TMV-infection induced typical ultrastructural changes in leaves such as the accumulation of virions aligned in parallel form throughout the cytosol. 3D reconstruction revealed that they form spherical viral inclusion bodies that either occur as single structures or are associated with each other and cover about 13% of the cell. These structures were closely associated with other cell compartments such as chloroplasts, vacuoles, peroxisomes, mitochondria and nuclei. TMV-infection strongly increased the area of starch (815%) in chloroplasts which is most probably caused by increased photosynthesis in these plants. Plastoglobuli area was increased in TMV-infected cells by about 100% whereas the area of thylakoids remained unchanged when compared to control plants. Summing up, the results of this study clearly demonstrate that TMV infection induced the accumulation of virions in the form of spherical inclusion bodies in the cytosol. These inclusion bodies were closely associated with other organelles.