Differential response of antioxidant genes in maize leaves exposed to ozone.

Antioxidant enzymes function to eliminate reactive oxygen species (ROS) produced as a consequence of normal metabolic functions as well as environmental stress. In these studies, the responses of catalase (Cat), superoxide dismutase (Sod) and glutathione S-transferase (Gst), as well as D-ribulose-1,5-bisphosphate carboxylase/oxygenase (RbcS) genes were analyzed in 9- and 15-day postimbibition maize seedlings exposed to various ozone (O3) concentrations and time periods. After a single (acute) 6 h exposure, or 3, 6 and 10 consecutive days (chronic) exposure to O3, Cat1, Cat3, Gst1, Sod3, Sod4 and Sod4A transcript levels generally increased, while Cat2, RbcS and Sod1 levels decreased. Such changes in mRNA levels do not necessarily reflect parallel changes in the protein products of these genes. Changes in transcript levels seemed to be correlated with the spatial location of the isozymes encoded by the genes. The results are discussed with respect to gene regulation and expression, and the localization and function of these antioxidant enzymes during ozone-mediated oxidative stress.