Antioxidant enzyme responses to chilling stress in differentially sensitive inbred maize lines

Antioxidant enzyme activities were determined at the first, third and fifth leaf stages of four inbred lines of maize (Zea mays L.) exhibiting differential sensitivity to chilling. Plants were exposed to a photoperiod of 16:8 L:D for one of three treatments: (a) control (25 degrees C), (b) control treatment plus an exposure to a short-term chilling shock (11 degrees C 1 d prior to harvesting), and (c) long-term (11 degrees C constant) chilling exposure, Catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (ASPX; EC 1.11.1.11), superoxide dismutase (SOD; EC 1.15.1.1), glutathione reductase (GR; EC 1.6.4.2), and monodehydroascorbate reductase (MDHAR; EC 1.6.5.4) activities were assessed. Reducing and non-reducing sugars and starch concentrations were determined as general metabolic indicators of stress. Reduced activities of CAT, ASPX, and MDHAR may contribute to limiting chilling tolerance at the early stages of development in maize. Changes in levels of sugar and starch indicated a more rapid disruption of carbohydrate utilization in comparison to photosynthetic rates in the chilling-sensitive line under short-term chilling shocks and suggested a greater degree of acclimation in the tolerant lines over longer periods of chilling.