Effect of Dimethoate and Chlorfenvinphos on Plasma Membrane Integrity ofSynechocystissp. PCC 6803

The organophosphorus (OP) insecticides dimethoate and chlorfenvinphos, at all selected concentrations (0–500 μmol liter−1), reduced the rate of accumulation of uranine and enhanced fluorescence quenching of 9-amino-6-chloro-2-methoxyacridine (ACMA). There was a significant nonlinear negative correlation between insecticide concentrations and uranine accumulation. The reduction in amount of uranine trapped inside the cells was greater in cultures treated with chlorfenvinphos, whereas quenching of ACMA fluorescence was found to be greater with dimethoate treatment. A marked difference between the effects of dimethoate and chlorfenvinphos on permeability changes in the plasma membrane ofSynechocystiswas also noted. The release of cellular organic carbon was observed at each concentration of chlorfenvinphos, whereas with dimethoate such an effect was noted at ≥200 μmol liter−1. The rate of uptake of substrates like 2-deoxyglucose and 2-aminoisobutyric acid (AIBA) was significantly (negatively) correlated with concentrations of both the insecticides. Chlorfenvinphos was more effective than dimethoate in reducing the active uptake of nonmetabolizable sugar and amino acid analogues.