Abstract: In order to study the effect of exogenous calcium chloride on the physiological and biochemical indexes of alfalfa (Medicago Sativa L.) seedlings under drought stress,exogenous calcium chloride(5,10,15,20 mmol·L^-1)was applied to alfalfa seedlings under simulated drought stress with 20%PEG (Polyethylene glycol) in this study. We analyzed the effects of exogenous calcium chloride on the contents of osmotic adjustment substances,chlorophyll,membrane permeability substances and antioxidant enzyme activities of alfalfa seedlings under drought stress. The optimal relieve concentration of exogenous calcium chloride was evaluated by the membership function method. The results showed that when no exogenous calcium chloride was applied,with the increase of PEG concentration,the content of soluble protein,soluble sugar and proline in alfalfa leaves increased first and then decreased,the content of malondialdehyde and relative conductivity increased gradually,and the content of chlorophyll decreased gradually. The changes of peroxidase activity,catalase activity and superoxide dismutase activity increased first and then decreased. According to the comprehensive analysis of 9 indexes,PEG stress concentration of 20% could effectively simulate the response of alfalfa seedlings to drought stress. When 10 mmol·L^-1 CaCl₂ was applied to alfalfa seedlings under 20%PEG stress,the content of soluble protein,proline and chlorophyll,the activity of peroxidase and catalase increased by 32.40%,31.10%,69.41%,21.39% and 6.87% respectively,and the relative conductivity decreased by 27.37%. When 15 mmol·L^-1 concentration of CaCl₂ was applied under 20% PEG stress,the content of soluble sugar increased by 14.17% and the content of malondialdehyde decreased by 36.36%. The activity of superoxide dismutase was the highest at 5 mmol·L^-1 concentration of CaCl₂. The comprehensive evaluation of subordinate function showed that suitable CaCl₂ concentration could alleviate the damage of drought to alfalfa seedlings and CaCl₂ concentration of 10 mmol·L^-1was the best in the study herein.

Key words: Alfalfa, PEG osmotic stress, Calcium Chloride, Physiological indexes, Antioxidant enzymes, Membership function analysis

摘要： 为探讨外源氯化钙对干旱胁迫下苜蓿（Medicago Sativa L.）幼苗生理生化指标的影响，本研究对20%聚乙二醇（Polyethylene glycol，PEG）模拟干旱胁迫下的苜蓿幼苗分别施加5，10，15，20 mmol·L^-1外源氯化钙，分析外源氯化钙对干旱胁迫下苜蓿幼苗叶片的渗透调节物质、叶绿素、细胞膜透性以及抗氧化酶活性的影响，并利用隶属函数法综合评价最佳外源氯化钙缓解浓度。研究结果表明：未施加外源氯化钙时，随着PEG胁迫浓度（10%，15%，20%，25%）的增加，苜蓿叶片的可溶性蛋白、可溶性糖和脯氨酸含量均呈先升后降的趋势，丙二醛含量和相对电导率逐渐增加，叶绿素含量逐渐降低，过氧化物酶、过氧化氢酶和超氧化物歧化酶活性均呈先升后降的趋势；综合分析显示，20% PEG胁迫浓度可以有效模拟苜蓿幼苗对干旱胁迫的反应；苜蓿幼苗在20% PEG胁迫下施加10 mmol·L^-1 CaCl₂后，幼苗叶片的可溶性蛋白含量、脯氨酸含量、叶绿素含量，过氧化物酶活性、过氧化氢酶活性最高分别增加了32.40%，31.10%，69.41%，21.39%和6.87%，相对电导率最低降低了27.37%；20% PEG胁迫下施加15 mmol·L^-1 CaCl₂后，可溶性糖含量最高增加了14.17%，丙二醛含量最低降低了36.36%；超氧化物歧化酶活性在20% PEG胁迫下施加5 mmol·L^-1 CaCl₂浓度为最高；隶属函数法综合评价显示，适宜CaCl₂浓度可以缓解干旱对苜蓿幼苗造成的伤害，本试验中以浓度为10 mmol·L^-1 CaCl₂缓解效果最佳。

关键词: 苜蓿, PEG渗透胁迫, 氯化钙, 生理指标, 抗氧化酶, 隶属函数