• cadmium (Cd);
  • calcium (Ca);
  • mitochondrial electron transport chain;
  • NADPH oxidase;
  • plasma membrane;
  • reactive oxygen species (ROS)


  • • 
    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 (inline image), 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 inline image production. This inhibition was reversed by calcium (Ca2+) and magnesium (Mg2+). In isolated mitochondria, Cd2+ increased inline image and H2O2 production. In intact roots, Cd2+ stimulated H2O2 production whereas it inhibited inline image 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 (≤ 1 h) consequence of exposure to Cd2+ in vivo is stimulation of ROS production in the mitochondrial electron transfer chain and inhibition of NADPH oxidase activity in the plasma membrane.