Effects of Na(2)SO(3) on the activities of antioxidant enzymes in geranium seedlings.

This study investigated the effects of Na(2)SO(3), which releases SO(2) in apoplastic water, on the growth of geranium seedlings and on the activities of various antioxidant enzymes including peroxidase. Sodium sulfite (Na(2)SO(3)) addition both inhibited primary root growth and stimulated lateral root growth of the seedlings respectively. In addition, the contents of chlorophyll and Rubisco protein of the seedlings were greatly reduced with Na(2)SO(3) treatment. Total peroxidase activities of the seedlings also increased proportionally with the amount of Na(2)SO(3), this presumably correlating with oxidative stress levels. Notably, about an 8-fold enhancement of total peroxidase activity occurred in seedlings treated with 60 nM Na(2)SO(3) at pH 4.0. This enhancement of total peroxidase activity was mainly due to the increase of a strong cationic isoperoxidase, strong anionic isoperoxidase and neutral isoperoxidase activities. The strong cationic isoperoxidase from geranium seedlings was found to be the same enzyme as PC3 from geranium callus in terms of its physicochemical and catalytic properties. Moreover, the activities of superoxide dismutase and glutathione reductase were greatly enhanced with Na(2)SO(3) treatments at pH 4.0 without significant alteration of catalase activity. These results suggest that Na(2)SO(3) exposure, activities the plants defense mechanism against the reactive oxygen species generated.