Similarities in the soluble protein profiles of leaf tissue following either a hypersensitive reaction to virus infection or plasmolysis

Cucumber cotyledons and cowpea leaves both react hypersensitively to tobacco necrosis virus (TNV) infection. The soluble fractions of these tissues, following virus-elicited necrosis, contained apparently novel proteins. The proteins from the two plant species are dissimilar regarding both molecular weight and chemical nature. The α and β fractions in cowpea are strictly proteinaceous, whilst the γ protein in cucumber, is a glycoprotein. Similar alterations to the soluble proteins in either plant type could be induced following a period of plasmolysis in mannitol at hypertonic concentration (0.5 M). Protoplasts isolated from both cucumber and cowpea tissue, plasmolysed as above, did not contain the induced protein fractions. Thus the proteins may be bound to the cell-wall, plasmalemma or present in the cellular free space. Similarities between the stress situation of plasmolysis or a hypersensitive reaction are discussed with a view to establishing the signal(s) for the synthesis or generation of the proteins, and their role and function in these plants, if any.