Effect of NaCl on Growth and Activities of Protective Enzymes in Seedlings of White Clovers(Trifolium repens L.)

The effect of NaCl stress on growth and protective enzymatic activity of White Clover was investigated using seedling grown in pots.Two salt-tolerant varieties(1212,83-160) and two salt-sensitive varieties(83-159,81-1) with different NaCl stress(0%,1%,3%,5% and 7%) were studied here.The survival rate,plant height,electrolyte leakage rate,as well as the activity of Superoxide Dismutase(SOD),Peroxidase(POD) and Catalase(CAT) was tested.Results showed that the survival rate and relative plant height of these four varieties decreased with increased NaCl concentration,while the electrolyte leakage rate increased.The survival rate and relative plant height of salt-tolerant varieties(1212,83-160) were significantly higher than that of salt-sensitive varieties(83-159,81-1);while the electrolyte leakage rate of salt-tolerant varieties(1212,83-160) was significantly lower than that of salt-sensitive varieties(83-159,81-1).This suggests that the cells of salt-sensitive varieties were damaged more seriously under NaCl stress.With the extension of NaCl stress time,the activity of SOD,POD and CAT were all sharply increased,then declined,and then increased again.There are significant differences between salt-tolerant and salt-sensitive varieties.The activities of SOD,POD and CAT in salt-tolerant varieties were lower than salt-sensitive varieties after five to ten days of NaCl stress.The activities of SOD,POD and CAT in salt-tolerant and salt-sensitive varieties were no different after twenty days of NaCl stress.These results suggest that the accumulation of reactive oxygen increased the enzymatic activity in salt-sensitive varieties in the earlier stage of NaCl stress more than that in salt-tolerant varieties.