Abstract: To investigate the effects of exogenous melatonin (MT) solution on seed germination and seedling growth of Medicago sativa L. under aluminum stress,‘WL525HQ’ (aluminum resistant) and ‘Suntory’ (aluminum sensitive) alfalfa were used as materials. The seeds were soaked with MT solution of different concentrations (0,100,200,400,800 μmol·L^-1),and the seed germination,seedling growth,and antioxidant physiology of seedlings were measured under aluminum stress (1 mmol·L^-1). The results showed that aluminum stress inhibited the seed germination and seedling growth of alfalfa. MT seed soaking alleviated the oxidative damage caused by aluminum stress by increasing the activity of antioxidant enzymes and reducing the accumulation of H₂O₂ and MDA. With the increase of MT solution concentration,alfalfa seed germination rate,germination potential,root length,plant height,biomass and root antioxidant enzyme activity increased first and then decreased,while H₂O₂ and MDA contents decreased first and then increased. The variation range of ‘WL525HQ’ was higher than that of ‘Suntory’. The effects of different concentrations of MT on alfalfa aluminum toxicity were evaluated by combining germination indexes,growth indexes,antioxidant enzyme activities,H₂O₂ and MDA contents. The results showed that 200 μmol·L^-1 treatment had the best effect,400 μmol·L^-1 was the second,and 800 μmol·L^-1 was the worst.

Key words: Melatonin, Alfalfa, Aluminum stress, Seed germination, Seedling growth

摘要： 为探明外源褪黑素（Melatonin，MT）溶液浸种对铝胁迫下紫花苜蓿（Medicago sativa L.）种子萌发及幼苗生长的影响，本试验以‘WL525HQ’（耐铝）和‘三得利’（敏铝）紫花苜蓿为材料，使用不同浓度MT溶液（0，100，200，400，800 μmol·L^-1）浸种，测定铝胁迫（1 mmol·L^-1）下种子萌发、幼苗生长、幼苗抗氧化生理等指标。结果表明，铝胁迫抑制了紫花苜蓿种子萌发及幼苗生长，MT浸种通过提高抗氧化酶活性、减少H₂O₂和丙二醛的积累来减轻铝胁迫给紫花苜蓿带来的氧化伤害；且随着MT溶液浓度的增加，紫花苜蓿种子发芽率、发芽势、根长、株高、生物量及根系抗氧化酶活性呈先升后降趋势，H₂O₂和丙二醛含量呈先降后升趋势，‘WL525HQ’的变化幅度高于‘三得利’。综合发芽指标、生长指标、抗氧化酶活性、H₂O₂和丙二醛含量评价不同浓度MT对苜蓿铝毒害的缓解效果表明：200 μmol·L^-1处理效果较好，400 μmol·L^-1次之，800 μmol·L^-1最差。

关键词: 褪黑素, 紫花苜蓿, 铝胁迫, 种子萌发, 幼苗生长