Temporal changes in oxidative stress and antioxidant activities in Ulva pertusa Kjellman

Abstract

Temporal changes in the oxidative stress and antioxidant system in Ulva pertusa Kjellman collected in July, September, and November was evaluated. The lipid peroxidation was decreased in September and re-increased in November. Glutathione, the major thiol antioxidant molecule, was mostly in reduced form in September, but the glutathione was more oxidized and the content was significantly decreased in November. Glutamylcysteine ligase (GCL), the rate limiting enzyme for glutathione synthesis, activity was increased in September and November. Among the enzymes for glutathione recycling, the glutathione peroxidase (GPx) activity was highest in September, while the glutathione reductase (GRd) activity was highest in November. The superoxide dismutase (SOD) activity was significantly increased after September. The results suggest that reduced oxidative stress in September was due to the increased ROS scavenging capacity. The elevated oxidative stress in November indicates that the ROS generation should be exceedingly high despite the adaptively increased GCL, GRd, and SOD activities in cold season. Catalase activity was decreased after September, which might be relevant to the control of hydrogen peroxide concentration as a signaling molecule to modulate intrinsic seasonal changes in the algal metabolism rather than to the antioxidant function.