Abstract: In order to clarify the promoting effect of zinc oxide nanoparticles（ ZnO NPs ）on seed germination and seedling growth of alfalfa under drought stress，Zhongmu No. 1 was used as the test material，and 10% PEG6000 solution was used to simulate drought stress. The effects of foliar spraying of different concentrations（ 0，5，10，20，50，100，200 mg/L） of ZnO NPs on seed germination and seedling growth were studied. The optimal concentration of ZnO NPs was used for seedling spraying test，and the effect of spraying ZnO NPs on the growth and physiological characteristics of alfalfa seedlings under drought stress was studied. The results showed that drought stress inhibited seed germination and seedling growth of alfalfa. Spraying ZnO NPs could promote the germination of alfalfa seeds under drought stress，the effect of 50 mg/L ZnO NPs was the best，and the germination rate，germination potential，germination index，vigor index，root length and fresh weight of seeds significantly increased by 73.91%，128.57%，108.25%，203.06%，45.54% and 60.81%，respectively，compared with drought stress treatment. Spraying ZnO NPs could alleviate the inhibition of drought stress on the growth of alfalfa seedlings，and 20 mg/L ZnO NPs had the best effect. Spraying 20 mg/L ZnO NPs on alfalfa seedlings showed that compared with drought stress treatment，the plant height，stem diameter，leaf area and aboveground fresh weight of seedlings treated with 20 mg/L ZnO NPs under drought stress significantly increased by 9.48%，30.53%，5.98% and 43.78%，respectively；the contents of chlorophyll a，chlorophyll b，total chlorophyll and carotenoid significantly increased by 21.14%，21.71%，23.66% and 24.00%，respectively；the relative conductivity and malondialdehyde（MDA）content decreased by 9.17%（p≥0.05） and 26. 22%（p<0.05），respectively；the contents of hydrogen peroxide（H_₂O_₂）and superoxide anion（O2·-）significantly decreased by 14. 38% and 14.11%，respectively；the activities of superoxide dismutase（SOD），peroxidase（POD），catalase（CAT），and ascorbic peroxidase（APX）significantly increased by 16.77%，8.12%，8.90%，and 23.70%，respectively；the proline content significantly increased by 13. 08%，while the soluble sugar content significantly decreased by 16.48%. In summary，ZnO NPs can effectively enhance plant tolerance to drought stress by improving the photosynthesis，antioxidant capacity，and osmotic regulation of alfalfa.

Key words: Alfalfa, Zinc oxide nanoparticles, Drought stress, Germination, Growth, Physiological characteristics

摘要： 为阐明纳米氧化锌（ZnO NPs）对干旱胁迫下紫花苜蓿种子萌发、幼苗生长的促进作用，以中苜1号紫花苜蓿为供试材料，采用10% PEG6000溶液模拟干旱胁迫，研究叶面喷施不同质量浓度（0、5、10、20、50、100、200 mg/L）ZnO NPs对种子萌发、幼苗生长的影响，并以确定的最佳ZnO NPs质量浓度进行幼苗喷施试验，研究喷施ZnO NPs对干旱胁迫下紫花苜蓿幼苗生长及生理特性的影响。结果表明，干旱胁迫抑制紫花苜蓿种子萌发和幼苗生长。喷施ZnO NPs可促进干旱胁迫下紫花苜蓿种子萌发，以50 mg/L ZnO NPs效果最好，种子的发芽率、发芽势、发芽指数、活力指数、根长和鲜质量分别较干旱胁迫处理显著提高73.91%、128.57%、108.25%、203.06%、45.54%和60.81%。喷施ZnO NPs可缓解干旱胁迫对紫花苜蓿幼苗生长的抑制，以20 mg/L ZnO NPs效果最好。用20 mg/L ZnO NPs进行紫花苜蓿幼苗喷施试验发现，与干旱处理相比，干旱胁迫下喷施20 mg/L ZnO NPs处理幼苗的株高、茎粗、叶面积、地上部鲜质量分别显著增加9.48%、30.53%、5.98%、43.78%；叶绿素a、叶绿素b、总叶绿素、类胡萝卜素含量分别显著提高21.14%、21.71%、23.66%、24.00%；相对电导率和丙二醛（MDA）含量分别降低9.17%（p≥0.05）和26.22%（p<0.05）；过氧化氢（H₂O₂）和超氧阴离子（O₂^·-）含量分别显著降低14.38%和14.11%；超氧化物歧化酶（SOD）、过氧化物酶（POD）、过氧化氢酶（CAT）、抗坏血酸过氧化物酶（APX）活性分别显著提高16.77%、8.12%、8.90%、23.70%；脯氨酸含量显著提高13.08%，可溶性糖含量显著降低16.48%。综上，ZnO NPs可通过提高紫花苜蓿光合作用、抗氧化及渗透调节能力，有效增强植株对干旱胁迫的耐受性。

关键词: 紫花苜蓿, 纳米氧化锌, 干旱胁迫, 萌发, 生长, 生理特性