紫花苜蓿对Cd胁迫的响应及品种差异研究进展

Response and intraspecific differences of alfalfa to cadmium(Cd)stress

为利用紫花苜蓿对Cd污染土壤进行修复和综合利用提供理论基础。综述了紫花苜蓿对Cd胁迫的响应,包括:紫花苜蓿的生长对Cd的响应存在"低促高抑"现象;紫花苜蓿对Cd吸收的可能途径包括根表皮质膜的H+交换、Ca^(2+)和Mg^(2+)阳离子通道,根际环境和Cd元素在土壤中的有效态等因素会影响紫花苜蓿对Cd的吸收;在Cd由根部向地上部转运的过程中,随着土壤Cd含量的增加,更多的Cd被累积在紫花苜蓿的根部;紫花苜蓿应对土壤Cd胁迫的调控机理包括信号分子调控、抗氧化系统调控、生物巯基化合物对Cd的螯合、调节Cd的亚细胞分布和耐Cd基因的表达等多个方面。总结了紫花苜蓿对Cd胁迫响应的品种差异,主要表现在:种子萌发和幼苗生长;根瘤生长、植株形态和生物量;生理指标;对Cd的吸收与累积等方面。今后的研究工作可重点关注品种差异评判标准的建立、差异显著品种的系统筛选、在分子水平上的响应机理及品种差异机理的分析等方面。

The responses of alfalfa（Medicago sativa L.）to Cd stress are reviewed in this paper, as follows：The response of alfalfa growth to Cd stress presented trends of promotion at low concentrations and inhibition at high concentrations. The stress damage caused by Cd on alfalfa was alleviated by physiological responses including antioxidative system activation changes in biological membrane permeability, photosynthesis regulation, and osmotic regulation. Possible Cd adsorption strategies included H＋exchange in the plasma membrane of the root epidermis and Ca^（2＋）and Mg^（2＋）cation channels in their roots. Cd uptake in alfalfa roots was affected by the rhizosphere environment and bioavailability of Cd in soil. When Cd transported from root to shoots, it accumulated in the roots of alfalfa with an increase of Cd content in the soil.Of alfalfa plants regulated their response to Cd stress with mechanisms included signal molecular regulation, antioxidant system regulation,combining Cd with thiols, subcellular distribution of Cd, and upregulation of Cd-resistant gene expression. H2 S, NO, and CO were considered possible signal molecules, while upregulation of heme oxygenase-1（HO-1）transcription and increased heme oxygenase（HO）activity could be the key to activating the antioxidant system. Intraspecific differences of alfalfa in response to Cd stress are also reviewed in this paper, including the following：Seed germination and seedling growth of alfalfa showed remarkable differences among cultivars under Cd stress,and the maximum Cd tolerance value of various alfalfa cultivars was more than nine times greater than that of the minimum value. Under Cd stress, there were remarkable differences in nodule growth, plant morphology, and biomass between alfalfa cultivars, and the root length was considered an important indicator in evaluating intraspecific differences. The changes in physiological indicators, such as glutathione reduc-tase（GR） and ascorbate peroxidases（APXs） activity, GSH, h GSH, chlorophyll, proline, and MDA concentrations, and the leakage rate of electrolytes were very different among various alfalfa cultivars under the same level of Cd stress. Absorption and accumulation of Cd in alfalfa also had intraspecific differences. Generally, Cd stress in alfalfa should be studied further in the future to establish criteria to judge intraspecific differences, studying significant differences in system selection, analysis at the molecular level of stress response mechanisms,and intraspecific differences to Cd stress as this would help provide theoretical and practical bases for using alfalfa for the restoration and utilization of Cd-contaminated soil.