Electron microscopic study of the chitosan effect on the intracellular accumulation and the state of tobacco mosaic virus particles in tobacco leaves
Influence of chitosan on the accumulation and state of tobacco mosaic virus (TMV) in the mesophyll cells of <i>Nicotiana tabacum </i>L. var Samsun leaves in early period of infection development (3 days after infection of leaves) has been studied. The virus accumulated in the cells of the leaves treated for 24 h before infection with chitosan to a leser degree than in the control cells. The chitosan affected the formation of TMV-specific granular and tubular inclusions which are known to consist of the viral replicase components. Three days after infection of the leaves treated with the chitosan, a typical sign of the infection development was the predominant formation of granular inclusions which are known to appear at the early stages of TMV replication. The infected cells of the leaves untreated with chitosan contained mainly tubular inclusions which had been shown previously to be formed from granular ones at the last stages of the infection process. This indicates that chitosan treatment of the leaves leads to a delay of the development of infection. In phosphotungstic acid-stained suspensions obtained from the infected leaves, abnormal (swollen and «thin») TMV particles were observed along with normal ones. The appearance of abnormal virus particles seems to be caused by virus-induced activation of intracellular lytic processes. The most lytic activity in the infected cells as well as the highest number of abnormal viral particles was observed under the chitosan action. Therefore, it appears that chitosan-mediated stimulation of lytic processes causing destruction of TMV particles may be one of the protective mechanisms limiting virus accumulation in cells.