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.) exhibiti ng differential sensitivity to chilling. Plants were exposed to a phot operiod of 16:8 L:D for one of three treatments: (a) control (25 degre es 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 d egrees C constant) chilling exposure, Catalase (CAT; EC 1.11.1.6), asc orbate peroxidase (ASPX; EC 1.11.1.11), superoxide dismutase (SOD; EC 1.15.1.1), glutathione reductase (GR; EC 1.6.4.2), and monodehydroasco rbate 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, ASP X, and MDHAR may contribute to limiting chilling tolerance at the earl y stages of development in maize. Changes in levels of sugar and starc h indicated a more rapid disruption of carbohydrate utilization in com parison to photosynthetic rates in the chilling-sensitive line under s hort-term chilling shocks and suggested a greater degree of acclimatio n in the tolerant lines over longer periods of chilling.