Superoxide dismutase and peroxidase are coordinately regulated in differentiated and transformed tissues of Nicotiana tabacum.

We used a series of normal and Agrobacterium-transformed, bacteria-free tobacco tissue cultures which differ in their levels of histodifferentiation to test the relationship of superoxide dismutase, peroxidase, and catalase to oncogenic transformation and differentiation. When compared with normal callus, tumor callus contained reduced levels of both superoxide dismutase and peroxidase, and a reduced number of isozymes of both enzymes. Teratomas characterized by limited but abnormal differentiation showed increases in superoxide-dismutase activity and isozymes, but levels of peroxidase activity lower than those found in normal callus despite an increase in the number of peroxidase isozymes. A similar disparity between low peroxidase activity and high isozyme number in the shoot suggests that there are increased levels of peroxidase inhibitors or of molecules which interfere with the spectrophotometric assay for peroxidase in more differentiated tissues. As judged by the number of isozymes of both superoxide dismutase and peroxidase in each tissue, the following conclusions are warranted: first, tobacco copper/zinc superoxide dismutases and peroxidases are encoded in several duplicated loci which are regulated independently. Second, transformation is associated with a decrease in both the specific activity and isozyme number of superoxide dismutase. Third, the partial release from the total inhibition of expression of differentiated function exhibited by teratoma is associated with an increase in both the activity and isozyme number of superoxide dismutase. Finally, the expression of superoxide dismutase and peroxidase isozymes appears to be coordinated during differentiation in a manner that is consistent with their role in an integrated mechanism for the removal of reduced oxygen species.