CHILLING, OXIDATIVE STRESS AND ANTIOXIDANT RESPONSES IN SHOOT CULTURES OF RICE

Chilling of shoot cultures from Oryza sativa L. cv, Taipei 309, to 4 d egrees C leads to conditions of oxidative stress. Tissue H2O2 was obse rved to increase more than fourfold by 8d of chilling, and levels of r educed glutathione, which normally rise in growing shoot cultures at 2 5 degrees C, were considerably repressed in chilled cultures. Whilst t he activity of ascorbate peroxidase in chilled shoots remained similar to the activities in control cultures at 25 degrees C, the most notab le effects of chilling to 4 degrees C were the very significant loss o f catalase and glutathione reductase activity. Although prior exposure of shoot cultures to abscisic acid (ABA) at 25 degrees C increased le vels of catalase activity, such increased levels were not sustained wh en the pre-treated cultures were placed at 4 degrees C. Moreover such pre-treatment with ABA did not increase the subsequent ability of shoo t cultures to grow at 4 degrees C.