Abstract: This study investigated the effects of Pb stress on the physiology of seed germination and the antioxidant system and Pb accumulation in seedlings of alfalfa （Medicago sativa）. Six Pb stress concentrations were set to evaluate seed germination physiology， and three Pb stress concentrations were established to assess the activity of the antioxidant system and Pb content in seedlings. The results showed that： （1）Pb stress inhibited seed imbibition and germination， reduced the activities of amylase and protease， and decreased the levels of soluble sugars， reducing sugars， free proline， and free amino acids. （2）The suitable concentration for Pb during seed germination of alfalfa was ≤1.84 mmol·L^-1， with a half lethal concentration and a limit concentration of 3.93 mmol·L^-1 and 7.29 mmol·L^-1， respectively. （3）Under 2.0 mmol·L^-1 Pb stress， the antioxidant system activity in seedling leaves initially increased and then decreased. At 4.0 mmol·L^-1 Pb stress， the antioxidant system collapsed， and oxidative damage intensified. （4）Under Pb stress， Pb content in seedlings significantly increased， with the highest levels in roots， followed by stems and leaves. Only a small amount of Pb translocated from underground to aboveground parts. This indicates that Pb stress inhibited seed germination， exacerbated oxidative damage in seedlings， led to the collapse of the antioxidant system， and caused substantial Pb accumulation in seedling roots. The study provides a theoretical basis for using alfalfa to remediate Pb-contaminated soils.

Key words: Alfalfa, Pb Stress, Germination physiology, Antioxidant system, Enrichment effect

摘要： 为探讨Pb胁迫对紫花苜蓿（Medicago sativa L.）种子萌发生理及幼苗抗氧化系统和Pb富集效应的影响，设置6个Pb胁迫浓度测定种子萌发生理，设置3个Pb胁迫浓度测定幼苗抗氧化系统活性及Pb含量。结果表明：（1）Pb胁迫抑制了种子的吸胀和萌发，淀粉酶和蛋白水解酶活性下降，可溶性糖、还原性糖、游离脯氨酸和游离氨基酸含量降低。（2）种子萌发期耐Pb适宜浓度为≤1.84 mmol·L^-1，半致死浓度和极限浓度为3.93 mmol·L^-1和7.29 mmol·L^-1。（3）2.0 mmol·L^-1 Pb胁迫下，幼苗叶片中抗氧化系统活性先升高后下降，4.0 mmol·L^-1 Pb胁迫导致抗氧化系统崩溃，氧化损伤加剧。（4）Pb胁迫下，幼苗体内Pb含量显著增加，且根系>茎秆>叶片，仅有少量Pb从地下部向地上部转运。Pb胁迫抑制了种子萌发，幼苗氧化损伤加剧，抗氧化系统崩溃，Pb在幼苗根系中大量富集。研究为利用紫花苜蓿修复Pb污染土壤提供了理论依据。

关键词: 紫花苜蓿, Pb胁迫, 萌发生理, 抗氧化系统, 富集效应