Abstract: To explore the impact of melatonin pretreatment on the drought resistance of alfalfa (Medicago sativa L.) seedlings,this experiment used ‘Zhonglu No.1’ alfalfa as the material,and set up 4 concentrations of polyethylene glycol and 5 concentrations of melatonin for germination experiments. Select the optimal concentrations of PEG and melatonin to treat alfalfa seedlings,and observe the phenotype and physiological indicators of alfalfa seedlings before and after treatment. The results showed that the seed germination rate,fresh weight and root length of seedlings were improved with 50 μmol·L^-1 and 100 μmol·L^-1 melatonin pretreatments under drought stress simulated by 10% PEG. Pretreatment with 50 μmol·L^-1 melatonin significantly increased the leaf water content,soluble sugar content and proline content of alfalfa seedlings under drought stress. Additionally,the electrolyte leakage and malondialdehyde content were significantly decreased,and the expression levels of genes related to antioxidant enzyme synthesis were significantly upregulated,leading to enhanced antioxidant enzyme activity. In this study,we verified that melatonin pretreatment at appropriate concentrations could effectively alleviate the damage caused by drought stress on alfalfa seedlings and enhance the drought resistance of alfalfa seedlings,which might provide a certain reference for the rational use of melatonin in drought-tolerant cultivation of alfalfa.

Key words: Melatonin, Drought stress, Alfalfa, Physiological response

摘要： 为探究褪黑素预处理对紫花苜蓿(Medicago sativa L.)幼苗抗旱性的影响，本试验以‘中苜一号’紫花苜蓿为材料，设置4个聚乙二醇(Polyethylene glycol，PEG)浓度和5个褪黑素浓度进行发芽试验，分别筛选出最佳的PEG和褪黑素浓度来处理紫花苜蓿幼苗，观测处理前后紫花苜蓿幼苗的表型及生理指标。结果表明，50 μmol·L^-1和100 μmol·L^-1褪黑素预处理能有效提高10% PEG模拟干旱胁迫下紫花苜蓿种子的发芽率、幼苗鲜重及根长；50 μmol·L^-1褪黑素预处理显著提高了干旱胁迫下紫花苜蓿幼苗的叶片含水量、可溶性糖含量和脯氨酸含量，另外，电解质渗透率和丙二醛含量均显著降低，抗氧化酶合成相关基因的表达水平显著上调，抗氧化酶活性增强。本研究验证了适宜浓度的褪黑素处理能有效缓解干旱胁迫对紫花苜蓿幼苗造成的损伤，增强紫花苜蓿幼苗的抗旱性，为褪黑素在紫花苜蓿耐旱栽培中的合理使用提供了一定的参考。

关键词: 褪黑素, 干旱胁迫, 紫花苜蓿, 生理响应