The expression level of a specific catalase isozyme of maize mutants alters catalase and superoxide dismutase during norflurazon-induced oxidative stress in scutella

The effect of catalase (CAT) levels on antioxidant responses to norflurazon (NF)-induced photooxidative stress was examined in 5-day postimbibition (dpi) scutella of a standard maize (Zea mays) CAT line (W64A) and various CAT mutants. In W64A and CAT-3 null (WI10D), CAT activities decreased at 1 μM NF and increased at 10 μM NF. The CAT activities of CAT-2 null (WA10C) and CAT-2/CAT-3 double null (WDN10) were very low throughout all treatments. The high CAT-2 activity mutant (R6-67) had decreased CAT activity but maintained the highest level among the various CAT lines upon NF treatment, and also had the highest level of SOD activity. Total SOD activity and SOD isozyme patterns were relatively consistent at NF concentrations of 1-10 μM in scutella of all maize CAT lines examined. The mutants lacking the CAT isozyme were capable of maintaining a high level of SOD in response to NF, demonstrating that SOD is the base-level scavenger of NF-mediated photooxidative stress. An increase in Cat1, Cat2, and Cat3 transcript levels occurred in scutella of R6-67, but not W64A following treatment with NF. All Sod transcript levels except the level of Sod1 responded differentially between NF-treated scutella of W64A and R6-67. W64A and maize mutant line expressing strong CAT-2 activity exhibited a different response to NF at the protein and mRNA levels of CAT and SOD. These results indicate that the level of a specific CAT isozyme in the maize mutants affects the levels of CAT and SOD.