CHILLING, OXIDATIVE STRESS AND ANTIOXIDANT RESPONSES IN ARABIDOPSIS-THALIANA CALLUS

Chilling of Arabidopsis thaliana (L.) Heynh. callus tissue to 4 degree s C led to conditions of oxidative stress, as indicated by increased l evels of the products of peroxidative damage to cell membranes. Cellul ar H2O2 was also observed to increase initially upon chilling but by d ay 8 cellular levels had declined to below control levels. Although le vels of catalase activity remained similar to those in unchilled tissu e, activity of ascorbate peroxidase increased between days 4 and 8 of chilling to 4 degrees C. In callus held at 23 degrees C, levels of red uced glutathione remained static whereas they rose in callus held at 4 degrees C. Levels of oxidised glutathione were initially low but incr eased significantly by day 4 in the chilled callus. At 23 degrees C, h owever, levels of oxidised glutathione remained low. Between days 1 an d 3 at 4 degrees C, levels of glutathione reductase activity increased but by day 8 glutathione reductase activity was similar to that in ce lls held at 23 degrees C. Exposure of callus to abscisic acid at 23 de grees C also led to increased activities of ascorbate peroxidase and g lutathione reductase.