Growth of Chlorella sorokiniana in the presence of sulfite elevates cell content of superoxide dismutase and imparts resistance towards paraquat.

1. Growth of Chlorella sorokiniana in the presence of 7.5 mM sulfite, which halved the growth rate while doubling the superoxide dismutase (SOD; EC 1.15.1.1) content per cell, rendered the cells resistant to the toxic effects of 30 μM paraquat. 2. While increasing total SOD content, sulfite increased the relative amount of the H2O2-resistant manganese-containing SOD. 3. It appears that O2 (-) may be involved in mediating the toxicity of SO2 in this green alga.