Differential antioxidant responses to norflurazon-induced oxidative stress in maize.

This study examined the contribution of catalase (CAT) and superoxide dismutase (SOD) in the overall antioxidant response to norflurazon (NF)-induced oxidative stress in leaves, mesocotyls and scutella of maize (Zea mays). Maize catalase null mutants were used to provide insights into the role(s) of these isozymes. A substantial increase in Cat1 and Cat2 transcript levels occurred in NF-treated leaves in all maize lines examined. However, these two transcripts did not show a particular pattern of change in NF-treated scutella from 5-day postimbibition (dpi) and 18-day postpollination (dpp) maize. The NF-induced increase in Cat1 appeared to be dependent on excessive light energy caused by a lack of photoprotectant carotenoids. especially in leaves. In NF-treated leaves, the chloroplastic Cu/Zn-SOD-1 isozyme responded strongly compared to the cytosolic Cu/Zn-SOD and mitochondrial Mn-SOD-3 isozymes, suggesting the critical role of SOD-1 as a major component in chloroplastic antioxidant defenses. All SOD isozymes in the NF-treated scutella of various maize lines were consistent in their response to NF. The most significant increase was observed with Sod1 in NF-treated leaves; however, no significant Sod1 changes were observed in similarly treated scutella at 5 dpi and 18 dpp. These results suggest that the response of the Cat and Sod genes to NF is likely developmental and tissue-specific.