Time-Dependent Oxidative Stress Responses of Submerged Macrophyte Vallisneria natans Seedlings Exposed to Ammonia in Combination with Microcystin Under Laboratory Conditions

We studied the antioxidant responses of macrophyte Vallisnerria natans seedlings to combined ammonia (0, 0.21, and 0.85 mg L-1) and microcystin-LR (MC-LR) (0, 10, and 50 mu g L-1) for 7 days. Results showed that superoxide dismutase, catalase (CAT), peroxidase, and glutathione were significantly induced by the mixtures of ammonia and MC-LR, and there were significant interactions between ammonia and MC-LR. Specially, CAT increased about fivefold at ammonia 0.85 mg L-1 and MC-LR 50 mu g L-1 on day 3. Malondialdehyde fluctuated with both ammonia and MC-LR, and significant interactions were detected between the two stressors. Changes in all the measured variables were time-dependent.