Ca2+-calmodulin-stimulated superoxide generation by purified plasma membrane from wheat roots

Abstract Highly purified plasma membranes were isolated by aqueous two-phase partitioning from wheat roots. The superoxide generation was studied by EPR technique with Tiron as the spin trap. Ca 2+ -calmodulin could stimulate the TH· signal, while SOD and several calmodulin antagonists, La 3+ , EGTA and CPZ could inhibit the TH· signal. Stimulation of TH· signal by Ca 2+ -calmodulin was dependent on NADH and calmodulin. The above results provided direct evidence for the connection of calmodulin to the redox system of plasma membranes. Similarly, catalase and KCN could also inhibit TH· signal. No stimulation of superoxide production was observed when Ca 2+ and calmodulin were added separately. NADPH could not elicit TH· signal in the study of the stimulation of superoxide by Ca 2+ -calmodulin. Triton X-100 (0.05%) could not cause a significant increase in TH· signal.