ULTRASTRUCTURE AND CYTOCHEMISTRY OF PHASEOLUS LEAF TISSUES INFECTED WITH AN ISOLATE OF TOBACCO NECROSIS VIRUS INDUCING LOCALIZED WILTING

The cytopathology induced by an isolate of tobacco necrosis virus (TNV-W) causing wilted, non-self-limiting lesions in Phaseolus bean was compared with that of abiotically-induced wilting. The main cell alterations specific to TNV-W infection were ER proliferation and vesiculation, plasmolysis and plasmalemma proliferation. Later there was lysis of most cell membranes, formation of crystalline inclusions in the chloroplasts and development of fibrous structures in the cytoplasm. It is suggested that the chloroplast inclusions consist of ribulose-1,5-bisphosphate carboxylase (Ru-BisCo). TNV-W replicated extensively in infected cells, often forming large crystalline aggregates of virus particles. Tissue wilting, as well as crystallization of the virus and RuBisCo, may have been caused by cell dehydration due to the loss of plasmalemma integrity.