A ROLE FOR SUPEROXIDE IN THE NaCl-INDUCED UPREGULATIONOF ANTIOXIDANT ENZYME ACTIVITY

摘要

Physiological stress induced by environmental factors results in an up-regulation of the antioxidant defense system and an increasein tolerance towards salt stress in cotton (Gossypium hirsutum). The mechanism which specifies salt-tolerance to anon-halophyte plant is not well understood. NaCl-induced up-regulation of antioxidant enzymes is thought to be impartedthrough a signal transduction cascade initiated through superoxide (O2-). This hypothesis was tested by using time-coursestudies in which antioxidant enzyme activity was measured in callus tissue from a NaCl-tolerant cell line subjected to NaCland 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 effectivelyscavenged ROS produced during either NaCl stress or paraquat stress in the NaCl-tolerant callus tissue. Pre-treatmentwith NAC also effectively inhibited the NaCl-induced up-regulation of catalase (CAT), general peroxidase (PER), ascorbateperoxidase (APX), and glutathione reductase (GR) during NaCl and paraquat stress. This NAC-driven consumption of ROSproduction strongly suggests that ROS do play a role in the NaCl-induced up-regulation of the stress response in cotton.