CYTOTOXIC EFFECTS OF P-BENZOQUINONE AND P-HYDROQUINONE ON CULTURED GRAPEVINE CELLS

Exogenous added p-benzoquinone and p-hydroquinone have a cytotoxic eff ect on cultured grapevine cells. IC50 values for loss of cell viabilit y were 0.1 mM for p-benzoquinone and 6.3 mM for p-hydroquinone. The to xicity of p-hydroquinone was probably related with its oxidation to p- benzoquinone by grapevine peroxidases. The cytotoxic effect of p-benzo quinone was not due to intracellular redox cycling of quinones, which would to lead membrane damage and plasma membrane rupture, since level s of the lipid oxidation products (i.e. malonaldehyde) remained below the limit of detection. Likewise, no changes in membrane permeability (electrolyte leakage) were observed after quinone treatment, as may be seen from the absence of changes in the conductivity of the spent med ium and pH. These results discard a possible role for the intracellula r redox cycling of quinones in order to explain quinone toxicity in pl ants.