Abstract: In order to explore the physiological mechanism of exogenous spermidine (Spd) to improve drought resistance and drought mitigation in alfalfa (Medicago Sativa L.),'Longmu No.807’cultivated by nutrient solution was used as the experiment material and 20% polyethylene glycol (PEG-6000) was used to simulate osmotic stress. The effects of spermidine with different concentrations (0,0.3,0.6，0.9,1.2 mmol·L-1)on membrane permeability substances,antioxidant enzyme activities,contents of osmotic adjustment substances and chlorophyll were analyzed. The optimal relieve concentration of exogenous Spd was evaluated by the membership function method.The results showed that when 0.9 mmol·L^-1Spd was applied to alfalfa seedlings under 20% PEG stress,the content of MDA and H₂O₂，O^-_2· production rate decreased by 37.29%，46.84% and 39.00%,respectively. The antioxidant enzyme activities of SOD and CAT increased by 65.75% and 60.21%,respectively. The contents of soluble protein,proline and chlorophyll increased by 93.27%，52.30% and 76.54%;respectively,when 0.6 mmol·L^-1Spd was applied to alfalfa seedlings under 20% PEG stress. The activity of POD increased by 26.07%. The contents of soluble sugar increased by 77.62% when 1.2 mmol·L^-1Spd was applied. The comprehensive evaluation of subordinate function showed that suitable Spd concentration could alleviate the damage of drought to alfalfa seedlings and Spd concentration of 0.9 mmol·L^-1 was the best in the study herein. Therefore,exogenous Spd could stabilize the cell membrane system,enhance the antioxidant capacity,maintain the osmotic balance,and alleviate the damage of drought to alfalfa seedlings.

Key words: Spermidine, Drought stress, Alfalfa, Physiological indexes

摘要： 为探讨外源亚精胺(Spd)提高苜蓿(Medicago sativa L.)抗旱的生理机制并为干旱缓解提供理论依据，本研究以'龙苜807’为材料，采用营养液法培养苜蓿幼苗，以20% PEG-6000模拟干旱胁迫，研究不同浓度的Spd (0，0.3，0.6，0.9，1.2 mmol·L^-1)对苜蓿幼苗叶片细胞膜透性、抗氧化酶活性、渗透调节物质及叶绿素的影响，利用隶属函数法综合评价外源Spd最佳缓解浓度。发现0.9 mmol·L^-1Spd 使干旱胁迫下苜蓿幼苗叶片丙二醛(MDA)含量、H₂O₂含量和O^-_2·产生速率降低37.29%，46.84%和39.00%；超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性增大65.75%和60.21%；可溶性蛋白和脯氨酸含量增加93.27%和52.30%；叶绿素含量增加76.54%；0.6 mmol·L^-1Spd 使干旱胁迫下苜蓿幼苗POD活性增加26.07%。1.2 mmol·L^-1Spd处理可溶性糖含量增加了77.62%。适宜Spd浓度可有效缓解干旱对苜蓿幼苗的伤害，以0.9 mmol·L^-1Spd为最佳。因此，外源Spd浓度可稳定苜蓿生物膜系统，增强抗氧化能力，维持细胞渗透平衡，有效缓解干旱对苜蓿幼苗的伤害。

关键词: 亚精胺, 干旱胁迫, 苜蓿, 生理指标