Expression level of specific isozymes of maize catalase mutants influences other antioxidants on norflurazon-induced oxidative stress

Abstract

The combined action of catalase (CAT) and superoxide dismutase (SOD) is critical in mitigating the effects of oxidative stress. The standard maize ( Zea mays) CAT line (W64A), CAT-2/CAT-3 double null mutant (WDN), and high CAT-2 activity mutant (R6-67) were used to examine whether absent or high expression of specific CAT isozymes influences the levels of SOD isozymes or non-enzymic antioxidant carotenoids, in response to norflurazon (NF)-induced oxidative stress. In leaves and mesocotyls of NF-treated W64A, there was a significant reduction in carotenoid, chlorophyll, and total CAT activity, but an increase in total SOD activity in leaves and an increase in anthocyanin in mesocotyls. W64A and WDN showed a great decrease in carotenoids and chlorophylls, while R6-67 sustained carotenoid level high and remained dark green at low NF concentrations. WDN had a lower CAT activity than W64A in control tissues and its CAT activity decreased further in response to NF, whereas R6-67 showed a smaller decline in CAT activity. These results suggest the critical role of CAT-2 isozyme in NF-induced oxidative stress. Total SOD activity increased slightly in response to NF in leaves of W64A, but remained almost constant in leaves of other lines and in mesocotyls of all the maize lines examined. Chloroplastic SOD-1, a dominant pathway during NF-induced enzymatic scavenging in W64A, did not increase in leaves of NF-treated WDN and R6-67. These results demonstrate that absent or high CAT activity influences the levels of photoprotective carotenoids and SOD in response to NF-induced oxidative stress.