An electron microscope study of hypersensitive tobacco infected with tobacco mosaic virus at 32 °C

Two tobacco species, Nicotiana glutinosa and N. tabacum cv. "Samsun NN" which react hypersensitively to tobacco mosaic virus (TMV), were inoculated at 32 °C and either maintained at this temperature or transferred to 22 °C after 7 days. An electron microscope study revealed that, after temperature transfer, there were large packets of crystal-like virus particles in collapsed cells, whereas in non-collapsed cells, at both temperatures, particles were randomly distributed. The nuclei of infected cells of plants maintained both at 32 °C and at 22 °C possessed large, centrally placed electron-translucent zones containing rod-shaped particles, possibly TMV. Since these were also found in cells of "Samsum" tobacco infected at 32 °C they are not features of the expression of the N gene. The dark-staining nucleoli in nuclei of both "Samsum NN" and N. glutinosa cells infected with TMV at 32 °C comprised two distinct zones, which may be associated with a switching-off of the N gene. A few chloroplasts in the ring of infected tissue surrounding green islands in plants carrying the N gene contained vesicular bodies. Generally, chloroplasts in this tissue became swollen, and displayed swelling of the thylakoids, followed by loss of the surrounding envelope. © 1976.