Changes in activity and transcription of antioxidant enzymes and heat shock protein 90 in the water flea, Daphnia magna - exposed to mercury

Abstract

Mercury (Hg) has adverse effects in aquatic organisms but mechanisms underlying the effects of Hg in aquatic invertebrates are unclear. To investigate the oxidative stress response in the water flea Daphnia magna to Hg, intracellular reactive oxygen species (ROS) level, glutathione (GSH) content, and glutathione S-transferase (GST) and superoxide dismutase (SOD) activities were measured. Subsequently, transcriptional profiles of antioxidant enzyme-related genes (three GST isoforms, glutaredoxin, glutathione peroxidase and thioredoxin) and stress protein (HSP90) were examined at different developmental stages, concentrations and exposure times. The intracellular ROS level decreased at 48 h, whereas the total GSH content was greatly increased at 48 h. A significant increase in GST and SOD activities was also observed at 48 h. All the antioxidant-related genes were upregulated in juveniles more than neonates at 24 h exposure to Hg (0.08 μg/L), and their expression pattern was differently modulated according to the developmental stage at 48 h. The expression of HSP90 mRNA was observed at 24 h exposure to Hg in neonate (0.08-2 μg/L) and in juvenile (2 μg/L). These findings imply that these antioxidant enzymes and stress protein may be involved in cellular protection to Hg-induced toxicity. This study would be helpful in understanding the molecular mode of action of Hg in D. magna.