Superoxide anion burst and taxol production induced by Ce in suspension cultures of Taxus cuspidata

Generation of reactive oxygen species (ROS) induced by Ce⁴⁺ in suspension cultures of Taxus cuspidata was investigated. The burst of superoxide anions (O₂√^?) occurred rapidly after the addition of Ce⁴⁺ and reached maximum at 4.3 h, while the total level of the cellular reactive oxygen species maintained unchanged. The intracellular superoxide dismutase (SOD) and catalase (CAT) were activated while the intra/extracellular peroxidases (PODs) were inhibited accompanying the O₂√^? burst. The pretreatment of the suspension cultures with diphenylene iodonium (DPI), a suicide inhibitor of the NADPH oxidase, blocked the O₂√^? burst, inhibiting the cell apoptosis and taxol production induced by Ce⁴⁺. These results show that NADPH oxidase played a key role in O₂√^? burst and O₂√^? served as a mediator of Ce⁴⁺ for cell apoptosis and taxol production. The pretreatments of the suspension cultures with anthracene-9-carboxylate, an ion-channel blocker, nifedipine, a Ca²⁺-channel blocker, neomycin, a phospholipase C (PLC) inhibitor, or suramin, a G-protein inhibitor, decreased O₂√^? burst induced by Ce⁴⁺. It is thus inferred that Ce⁴⁺-induced O₂√^? burst, which mediated cell apoptosis and taxol production by activating the ion-channels, PLC, G-proteins and NADPH oxidase.