A rapid and concentration-dependent generation of superoxide anion （·O2^-）, measured with a superoxide-specific Cypridina luciferin-derived chemiluminescent reagent, was observed when two lanthanide salts （LaCl3 and CdCl3 ） were added to tobacco （ Nicotiana tabacum） cell suspension culture. Addition of superoxide dismutase （480 U·ml^-1） and Tiron （5 μmol·L^-1） to cell culture suspension decreases the level of lanthanide cation-induced ·O2^- generation, suggesting that ·O2^- generation is extra-cellular. Pretreatment of the cell culture suspension with diphenyleneiodonium （10 and 50 μmol·L^-1 ）, quinacrine （ 1 and 5 mmol· L^-1 ） and imidazol （ 10 mmol· L^-1 ）, inhibitors of NADPH oxidase, notably inhibits the generation of superoxide induced by lanthanide cation, implying the possible involvement of activation of NADPH oxidase. In addition, addition of SHAM （1 and 5 mmol· L^-1）, azide （0.2 and 1 mmol· L^-1 ）, inhibitor of peroxidase, has no influence on ·O2^- generation.
