Effects of Ammonia Stress on Metabolic and Antioxidant Enzyme Activities in Panulirus ornatus

Abstract:

In this study, in order to explore the effects of acute ammonia stress on the antioxidant and ammonia-nitrogen metabolism systems of Panulirus ornatus, lobsters were exposed to different concentrations of ammonia (0.24±0.07, 1.04±0.08, 9.75±0.21, and 19.87±0.46 mg/L) for up to 48 h. The activity of antioxidant and ammonia-nitrogen metabolizing enzymes and related gene expression were assessed in the gills and hepatopancreas at 0, 6, 12, 24, and 48 h after ammonia stress. From 6 to 12 h, total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) activity in the gills and hepatopancreas of P. ornatus under ammonia nitrogen stress increased to varying degrees, and was significantly higher than that of the control group (P<0.05). In the high-concentration group, T-AOC and SOD activity was inhibited for 48 h. The LPO content gradually increased with prolonged stress and was significantly higher than that of the control group (P<0.05) at 48 h. The activities of the ammonia metabolism enzymes glutamine synthetase (GS), glutamate dehydrogenase (GDH), glutamic-oxalacetic transaminase (GOT), and xanthine oxidoreductase (XOD) were all up-regulated to varying degrees under ammonia stress compared with those of the control group, indicating that they are jointly involved in the metabolic transport of NH4+. Additionally, from 12 to 24 h, the expression of GDH and GOT genes in the hepatopancreas was significantly higher than that of the control group (P<0.05); the same trend was identified in gill tissue. In brief, different concentrations of ammonia stress induce different levels of antioxidant enzyme activity. Panulirus ornatus mainly synthesizes glutamine under the combined action of hepatopancreas GS, GDH, and other metabolic enzymes to avoid excessive ammonia in the body.