少根紫萍对镉离子吸收、转运和解毒的分子机制研究

The environmental contamination usually comes along with the industrialization in our country, and cadmium in aquatorium has already been a great threat to people’s health. Therefore, it is very important and necessary to find a convenient way of retrieving cadmium from water. Duckweeds are the fastest growing and morphologically simplest of aquatic flowering plants, which grow rapidly on the water surface and efficiently absorb cadmium. So it is considered as an available engineering aquatic plant for phytoremediation. However, the related molecular mechanism of cadmium absorption, translocation and detoxification were poorly understood. Recently, a high cadmium-resistant species of duckweed, Landoltia punctata strain 52a-L, has been selected from more than two hundreds kinds of wild-type duckweeds in our repository. The accumulation of free proline and soluble phenolics and the induction of three cadmium translocation and detoxification related genes indicate that an internal mechanism will be activated with cadmium stress in Landoltia punctata strain 52a-L. According to these results, the molecular mechanism of cadmium absorption, translocation and detoxification will be further investigated in this project. Non-invasive micro-test technique will be used to determine the position and rate of cadmium absorption. Histochemical assays, fluorescence microscopic observations and energy dispersive x-ray microanalysis will be performed to exhibit the distribution of cadmium in Landoltia punctata strain 52a-L. Then, several physiological responses induced by cadmium stress will be detected. Moreover, differentially expressed genes will be identified and analyzed by transcriptome sequencing. Based on the results of these experiments, it will be exposed what is the major strategy of cadmium absorption, translocation and detoxification in Landoltia punctata strain 52a-L and which genes play the core effects in this process. Finally, the mechanism of cadmium absorption, translocation and detoxification in Landoltia punctata strain 52a-L will be revealed and provide new insights into engineering aquatic plants for phytoremediation.

镉是工业生产中重要的加工材料，也是一种对生物体有很强毒害作用的重金属。目前，镉造成的环境污染已日趋严重，如何有效清除镉已成为亟待解决的重要课题。浮萍具有高效吸收镉离子的能力，因而被看作是治理镉污染的有效途径之一。然而，浮萍对镉离子吸收、转运和解毒的分子机制仍不清晰。我们前期工作筛选获得一株具有较强镉耐受能力的少根紫萍品系，并通过检测游离脯氨酸和可溶性酚的含量变化，以及分析镉离子转运和解毒相关基因的表达水平，初步反映出少根紫萍具有一套内在的镉离子转运和解毒机制。本项目将继续分析镉胁迫引发的各种抗逆生理响应，确定它吸收和储存镉离子的部位，解析全基因组范围内基因表达水平的差异性，挖掘调控镉离子吸收、转运和解毒的关键基因，阐明少根紫萍对镉离子吸收、转运和解毒的分子机制，为未来通过基因工程手段定向改良浮萍或其它植物提供理论基础和技术支持。

镉是工业生产中重要的加工材料，也是一种对生物体有很强毒害作用的重金属。目前，镉造成的环境污染已日趋严重，如何有效清除镉已成为亟待解决的重要课题。浮萍具有高效吸收镉离子的能力，因而被看作是治理镉污染的有效途径之一。然而，浮萍对镉离子吸收、转运和解毒的分子机制仍不清晰。. 本研究已从200多种野生浮萍品种中筛选获得一株具有较强镉耐受能力的少根紫萍品系（Landoltia punctata 6001）。进一步的研究发现在镉胁迫条件下，少根紫萍6001能够保持一定的生长速率，并且其体内光合色素、过氧化氢、游离脯氨酸和可溶性酚酸的含量，随着镉处理时间的延长逐渐降低，初步解析了浮萍耐受镉胁迫的生理机制。同时，少根紫萍6001的根和叶状体均参与了对镉离子的吸收，但镉离子在浮萍体内的分布呈现出不均一性。少根紫萍6001体内可以富集超过1 mg/g的镉离子，远高于定义超富集植物标准的0.1 mg/g，展现出优良的应用潜质。通过转录组测序分析，全面系统的揭示了少根紫萍6001耐镉的分子机制。从DNA到RNA再到蛋白质的合成和调控系统对镉胁迫产生了显著的响应。并且，植物细胞壁的主要成分纤维素，半纤维素，果胶和木质素的合成受到了明显的抑制。此外，硫代谢途径，活性氧代谢途径，液泡区隔化过程，三羧酸循环和黄酮合成途径均在浮萍耐镉方面发挥了重要的作用。在解析浮萍耐镉分子机制的同时，还筛选到了3个浮萍耐镉机制中的关键基因，它们分别是参与液泡区隔化过程的LeHMA5，调控黄酮合成的LeMYB12和硫代谢途径中的LeGST30。这3个关键基因的过表达浮萍株系，均表现出更高的镉耐受能力。. 综上所述，本研究已经较为全面和系统地揭示了少根紫萍耐受镉胁迫的生理机制和分子机制。初步验证了浮萍耐镉机制中，3个关键基因的生物学功能。为今后创制在含镉污水治理方面具有更为优良特性的浮萍种质提供了明确的候选基因。