A rapid and concentration-dependent generation of superoxide anion （·O-2）, measured with a superoxide-specific Cypridina luciferin-derived chemiluminescent reagent, was observed when two lanthanide salts （LaCl3 and GdCl3） 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 ·O-2 generation, suggesting that ·O-2 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 ·O-2 generation.
