Origin of cadmium-induced reactive oxygen species production: mitochondrial electron transfer versus plasma membrane NADPH oxidase

Cadmium (Cd²⁺) is an environmental pollutant that causes increased reactive oxygen species (ROS) production. To determine the site of ROS production, the effect of Cd²⁺ on ROS production was studied in isolated soybean (Glycine max) plasma membranes, potato (Solanum tuberosum) tuber mitochondria and roots of intact seedlings of soybean or cucumber (Cucumis sativus). The effects of Cd²⁺ on the kinetics of superoxide ( [graphic removed] ), hydrogen peroxide (H₂O₂) and hydroxyl radical ( OH) generation were followed using absorption, fluorescence and spin-trapping electron paramagnetic resonance spectroscopy. In isolated plasma membranes, Cd²⁺ inhibited [graphic removed] production. This inhibition was reversed by calcium (Ca²⁺) and magnesium (Mg²⁺). In isolated mitochondria, Cd²⁺ increased [graphic removed] and H₂O₂ production. In intact roots, Cd²⁺ stimulated H₂O₂ production whereas it inhibited [graphic removed] and OH production in a Ca²⁺-reversible manner. Cd²⁺ can be used to distinguish between ROS originating from mitochondria and from the plasma membrane. This is achieved by measuring different ROS individually. The immediate (