Effect of Low Temperature Stress on the Survival and Physiological and Biochemical Indexes of Alfalfa Seedlings

Eleven Alfalfa(Medicago sativa L.) cultivars, which level of fall dormancy is from 2 to 9 were selected and planted in pots in this experiment.Every alfalfa cultivars was divided into six groups(a control and five treatments) randomly.The effect of low temperature stress and alfalfa cultivars on the survival rate,physiological and biochemical indexes of alfalfa seedlings was studied.The results showed that the effect of low temperature stress,alfalfa cultivars and interaction between them on the survival rate and physiological and biochemical indexes of alfalfa seedlings was very significant. For the seedlings having two cotyledons,when they were exposed to the temperature of-7.5 ℃ for about 12 h,the survival rate was only 3.26 %.When they were exposed to the temperature of-5 ℃ about 12 h,the survival rate was 54.73 % and free proline content,peroxide isozyme(POD) activity,membrane relative penetration in the leaves and root vitality showed a significant increase than the control.If the seedlings were exposed to the temperature of-5 ℃ for about 2 h ～3 h per day for 7 days,survival rate would significanttly increase(95 %).Free proline content,(soluble) sugar,soluble protein,superoxide dismutase(SOD),activity,root vitality and membrane relative penetration in the leaves also showed very significant increase.Results also showed that for the survival rate,the cultivars which level of fall dormancy is from 4 to 9 appeared significantly lower than those which level of fall dormancy is from 2 to 3.And the similar results occurred in the free proline content,POD activity and membrane relative penetration.