A ROLE FOR SUPEROXIDE IN THE NaCl-INDUCED UP-REGULATION OF ANTIOXIDANT ENZYME ACTIVITY

摘要

Physiological stress induced by environmental factors results in an up-regulation of the antioxidant defense system and an increase in tolerance towards salt stress in cotton (Gossypium hirsutum). The mechanism which specifies salt-tolerance to a non-halophyte plant is not well understood. NaCl-induced up-regulation of antioxidant enzymes is thought to be imparted through a signal transduction cascade initiated through superoxide (O_2). This hypothesis was tested by using time-course studies in which antioxidant enzyme activity was measured in callus tissue from a NaCl-tolerant cell line subjected to NaCl and paraquat stress in the presence and absence of a reactive oxygen species (ROS) scavenger, N-acetyl L-cysteine (NAC). An increase in superoxide anion production was observed in both NaCl- and paraquat-stressed callus tissue, and NAC effectively scavenged ROS produced during either NaCl stress or paraquat stress in the NaCl-tolerant callus tissue. Pre-treatment with NAC also effectively inhibited the NaCl-induced up-regulation of catalase (CAT), general peroxidase (PER), ascorbate peroxidase (APX), and glutathione reductase (GR) during NaCl and paraquat stress. This NAC-driven consumption of ROS production strongly suggests that ROS do play arole in the NaCl-induced up-regulation of the stress response in cotton.