Abstract: In this study,the ‘Ganong 5th’ alfalfa (Medicago sativa L.) was used as experimental material,and two application methods (leaf application,root application) and six exogenous betaine concentrations (0,10,20,30,40 and 50 mmol·L^-1) were used to treat the seedlings of alfalfa. Plant growth and related physiological indexes were measured after 7 days of low temperature (4℃) stress,and the physiological mechanism of exogenous betaine to alleviate the low temperature stress of alfalfa was explored. The results showed that exogenous GB alleviated the loss of plant height,root length,leaf dry weight,root dry weight and chlorophyll content,and increase the content of soluble sugar (SS) and free proline (Pro),and reduced the increase in leaf relative membrane permeability and MDA content. Exogenous GB increased antioxidant enzyme activities and non-enzymatic antioxidant content. And also,exogenous GB enhanced the osmotic adjustment capacity of the plant by increasing endogenous GB accumulation and BADH activity. These results indicated that exogenous GB enhanced the resistance of Medicago sativa to low-temperature stress under low temperature adjustment. The membership function analysis indicated that spraying 30 mmol·L^-1 GB on the leaves and spraying 40 mmol·L^-1 GB on the roots had the best effect on alleviating the low-temperature stress of alfalfa seedlings.

Key words: Low-temperature stress, Glycine betaine, Medicago sativa, Physiological characteristics

摘要： 本研究以‘甘农5号’紫花苜蓿（Medicago sativa L ‘Gannong No.5’）品种为实验材料，设置两种施加方式（叶施、根施）和六个外源甜菜碱浓度（0，10，20，30，40和50 mmol·L^-1）处理苜蓿幼苗，在低温（4℃）胁迫7 d后测定其生长和相关生理指标，探究外源甜菜碱缓解苜蓿低温胁迫的生理机制。结果表明，叶施和根施外源甜菜碱均能够有效缓解低温胁迫下苜蓿幼苗苗长、根长、地上及地下生物量和叶绿素含量的降低，增加可溶性糖和游离脯氨酸的含量，减少叶片相对膜透性和丙二醛含量的升高，显著提高抗氧化酶活性以及非酶抗氧化物质含量，同时，外源甜菜碱还可以促进低温胁迫下苜蓿幼苗内源甜菜碱的积累和甜菜碱脱氢酶活性，增强渗透调节能力，进而提高苜蓿对低温胁迫的抗性。通过隶属函数分析得出，叶施30 mmol·L^-1和根施40 mmol·L^-1的外源甜菜碱对缓解苜蓿幼苗低温胁迫的效果最佳。

关键词: 低温胁迫, 甜菜碱, 紫花苜蓿, 生理特性