Light and electron microscopy of cells infected with tobacco necrosis and satellite viruses.

Abstract

SUMMARY French-bean leaves inoculated with the stipple streak strain of tobacco necrosis virus alone or mixed with the satellite virus were examined microscopically. Light microscopy showed two types of inclusion in some living epidermal cells, one hyaline, the other granular and containing small crystals. Some cells also contained crystals different in form from those in the inclusions. Light microscopy of parenchymatous cells fixed and stained for electron microscopy showed only one type of inclusion, with smooth appearance. The crystals seen in the living cells were not found, but some cells from leaves infected with the mixture had areas containing both heavily stained amorphous material and bodies 1 to 2 ¼m. across. Electron microscopy of thin sections of the same fixed and stained material showed some cells to contain a structureless, electron-dense material, prominent cytoplasmic membranes and many vesicles, especially from leaves inoculated with the mixture. The electron-dense material often contained satellite virus in crystalline arrays and sometimes rhombic plates 1 to 2 ¼m. long. Whenever satellite virus was identified, tobacco necrosis virus occurred near to it. Cells infected with tobacco necrosis virus alone had well-defined areas in which the virus was concentrated and apparently uncontaminated. These areas corresponded to the inclusions seen in the light microscope. The relative frequency with which particles of the two viruses were detected by electron microscopy of leaf sections differed from the relative concentration of the two estimated by serological assays on sap extracted from leaves inoculated with the mixture.