Sequence of cytological events during the process of local lesion formation in the tomato bushy stunt virus-Gomphrena globosa hypersensitive system.

The ultrastructure of necrotic local lesions induced by tomato bushy stunt virus in Gomphrena globosa was studied during the first stages of development (24–64 hr postinoculation), in an attempt to define a sequence of cytological events possibly correlated with the mechanism of localization. The main cell alterations observed in the infection center were seen to appear in this order: swelling of the chloroplast thylakoids, alterations in shape of the chloroplasts and appearance of multivesicular bodies, appearance of virus particles, cell plasmolysis with callose deposits, necrosis. No deposition of lignin or suberin was observed in the infection stages examined. These results indicate that, at least in this virus—host combination, no “barrier substance” appears soon enough to be considered effective in preventing virus spread.