Abstract: Coumarin and Caffeic acid were identified as the major autotoxins of alfalfa (Medicago sativa L.). To provide a basis for further understanding their effects on the growth and development of alfalfa,an experiment of the nutrient solution sand culture was used with addition of exogenous coumarin,caffeic acid and their mixture at concentration gradient of 0,0.5,5,50,500 mg·L^-1. ‘Gannong No.9’ alfalfa was used here. Paraffin Sectioning Technique and the root scanning system were used to compare the effects of exogenous additives on the root morphological parameters such as total root length,total root surface area,root volume,and root tip number and on root anatomical indexes such as root thickness,cortical thickness,diameter and development of vascular cylinder,number and area of xylem vessels. The results showed that root morphological parameters such as total root length,total root surface area,root volume,and root tip number of the alfalfa were promoted under low concentration (0.5 mg·L^-1) of coumarin,caffeic acid and mixture. When the concentration of the additives increased to 50 mg·L^-1 or above,it showed autotoxic inhibition effects. The root anatomical indexes such as root thickness,cortical thickness,diameter and development of vascular cylinder,number and area of xylem vessels were promoted by coumarin and mixture at concentrations less than 5 mg·L^-1. And autotoxic inhibition effects by caffeic acid and mixture were at concentrations higher than 50 mg·L^-1.For the external morphology and internal anatomical structure of roots at low concentration (0.5 mg·L^-1) treatments,the promoting effect of the mixture was significantly stronger than the monomeric coumarin and caffeic acid (P<0.05),and the order of promotion from strong to weak was as follows:mixture > coumarin > caffeic acid. At high concentration (500 mg·L^-1),the autotoxic inhibition effects of coumarin and mixture was significantly stronger than the caffeic acid (P<0.05),the order of overall inhibition effect was as follows:coumarin > mixture > caffeic acid.

Key words: Coumarin, Caffeic acid, Alfalfa, Root morphology, Anatomical structure

摘要： 香豆素、咖啡酸为紫花苜蓿（Medicago sativa L.）主要自毒物质。本研究采用营养液沙培法，对甘农9号紫花苜蓿进行浓度梯度为0，0.5，5，50，500 mg·L^-1的外源香豆素、咖啡酸分别单种物质添加和混合物质添加试验，运用石蜡切片技术和根系扫描系统，比较研究外源添加物对苜蓿总根长、总根表面积、根体积、根尖数等根系形态指标与根粗、皮层厚度、中柱直径及发育、导管数量及面积等解剖结构指标的影响，为进一步研究香豆素和咖啡酸对紫花苜蓿生长和发育影响机理提供依据。结果表明：苜蓿总根长、总根表面积、根体积、根尖数等根系形态指标在低浓度（0.5 mg·L^-1）香豆素、咖啡酸及混合物作用下均呈促进作用，当添加物浓度增至50 mg·L^-1及以上时，呈自毒抑制作用。苜蓿根粗、皮层厚度、中柱直径及发育、导管数量及面积等内部解剖结构在浓度低于5 mg·L^-1的香豆素和混合物作用下呈促进作用，在高于50 mg·L^-1的咖啡酸和混合物处理下呈自毒抑制作用。根系外部形态和内部解剖结构在低浓度（0.5 mg·L^-1）处理时，混合物的促进作用显著强于单体香豆素和咖啡酸（P<0.05），促进作用由强至弱的顺序为：混合物 > 香豆素 > 咖啡酸，在高浓度（500 mg·L^-1）处理时，香豆素和混合物的自毒抑制作用显著强于单体咖啡酸处理（P<0.05），抑制综合效应由强到弱依次为：香豆素 > 混合物 > 咖啡酸。

关键词: 香豆素, 咖啡酸, 紫花苜蓿, 根系形态, 解剖结构