Physiological Response of Spartina alterniflora Seedlings to NaCl, CdCl2 and Their Interactions Stress

Pot experiment was conducted to study the change regulation of osmotic adjustment substance and antioxidant enzyme in leaves of Spartina alterniflora seedlings under salt stress and heavy metal stress. When the CdCl2 concentration in the range of 02-08mmol/L, the group under interaction stress with high concentration of NaCl (700, 900mmol/L) were dead. The results indicated that NaCl and CdCl2 interaction stress does not promote salt tolerance mechanism of Salterniflora seedlings, but accelerated its demise. The concentration of Salterniflora seedling growth decreased under the interaction stress, and the maximum NaCl tolerance concentration was 500mmol/L. Under different concentrations of CdCl2 in the 4 groups,the activity of superoxide dismutase (SOD), peroxidase (POD) and soluble protein content (SPC) in leaves of Salterniflora increased, and the three indicators increased first and then decreased, showing a single peak trend with the increase of NaCl concentration. SPC reached the peak at the NaCl concentration of 500-700mmol/L. The maximum of POD activity appeared at the NaCl concentration of 500-900mmol/L. The maximum of SOD activity appeared in the treatment group with low stress concentrations, suggesting that SOD was appeared in the antioxidant process prior to the other two kinds of antioxidant enzymes. SOD activity was negatively correlated with POD activity and CAT activity, but not significant (P > 005). And only free proline of osmotic adjustment substance and POD activity of antioxidant enzyme presented significantly positivecorrelation (P < 005). Comprehensive consideration of the various indicators, the results showed that SPC of osmotic adjustment substance, SOD activity of antioxidant enzyme and POD activity were more sensitive and showed the same change regulations under the stress concentrations of CdCl2 and NaCl at the range of 0-08mmol/L and 0-900mmol/L, respectively.