Further studies on ultrastructure of plants infected withPetunia ringspot virus

Summary New methods of fixation and embedding have revealed in plants infected withPetunia ringspot some structural features not described before. These include the X-bodies, 80 per cent of which are formed by tubular elements which are responsible for the positive staining specific for Golgi apparatus. The tubular elements are morphologically similar to agranular endoplasmic reticulum as described in some animal cells. The rest of the inclusion is formed by normal cytoplasmic elements in which are embedded long rod-shaped tubules 600 Å wide and more than 7,000 Å long, cross sections of which are formed by 10 subunits. These subunits are arranged in a helical way to form the large tubules. These subunits are probably the actual virus particles, which would be icosahedral and would form tubular crystals. Icosahedral virus particles would also form true crystalline inclusions.It is not known what the role of the agranular endoplasmic reticulum and of some dense osmiophilic bodies found in it may be in the multiplication of the virus. However, these components induced by the virus infection probably result in the manufacture of some proteins or other substances necessary for virus multiplication.