柳树根系重金属的微区分布特征、赋存形态及其耐性机制研究

Heavy metal contamination is a widespread and important environmental concern. Various in situ and ex situ cleanup technologies have been employed，of which phytoremediation is promising due to its low implementation costs and significant environmental benefits. The root is the first plant part to encounter soil heavy metal pollution, therefore the tolerance mechanisms in root are vital to the survival and establishment in contaminated soil . .To cope with metals in the medium, plants envolved a number of strategies to resist the toxicity of heavy metals include sequestration in specific cells and chelation with various ligands for detoxification. Therefore, resolving metal distribution, speciation and chemical forms in plants is essential for understanding the mechanisms involved in metal tolerance, detoxification, transporting and accumulation. Salix spp. have been proposed both for stabilisation and removal of metals from contaminated soils as they are fast to propagate, achieve high biomass production and generally possess a high tolerance against metal pollution. The aim of this project is to obtain fundamental information on heavy metal tolerance and detoxification mechanisms in roots of Salix integra by investigation of metal localization and ligand abundance. .In this study, the micro-distribution and chemical speciation of Lead(Pb) and Zinc(Zn) in roots of S. integra were detected by histochemical method, synchrotron-based micro-X-ray fluorescence (μ-XRF) and X-ray absorption fine structure spectroscopy (XAFS). We plan to analyse the subcelluar distribution and contents of Pb and Zn in root surface and cytoplasm of S. integra for the aim of revealing the function of root surface barrier and ligands during the metal adsorption and uptake process. This will explain the avoidance strategies and metal conpartmentalization in willow roots. To discuss the detoxification of metals in cytoplasm, chemical speciation of Pb and Zn would be determined by μ-XAFS. According to the information on the coordination between metals and the essential elements such as S, O and N in root cell, the comlexation reaction in metal detoxification will be predicted. This will provide insight into the strategies for heavy metals exclusion and detoxification in woody plants.

工业的发展和人类活动的增加，导致土壤重金属污染越来越严重，严重危害着人类健康。植物修复技术成为当前国际上治理大面积土壤污染最经济有效的方法，植物在抵御和适应重金属胁迫过程中，根系对重金属的耐性关乎植物在污染环境中的生存与定植，因此，深入了解根系对重金属的耐性与解毒机制，将为寻找理想的植物修复材料和提高植物修复效率奠定理论基础。本项目以杞柳（Salix integra Thunb.）栽培品种为研究对象，在传统的组织化学方法和元素分析技术基础上，结合同步辐射X-射线荧光微分析（μ-XRF）以及X-射线吸收精细结构(XAFS)分析技术，对Pb和Zn在杞柳根细胞和亚细胞的微区分布及区隔特征，根系细胞中Pb和Zn存在的化学形态、主要有机配位体及其螯合机制等进行了系统研究，以期阐明柳树在解除重金属毒害过程中根系的避性机制与螯合解毒方式，为木本植物在土壤污染治理中的应用提供可靠的科学理论依据。

重金属污染土壤的树木修复技术是近10年来植物修复领域关注的热点问题。柳树既是用于植物修复的理想材料，也是开展木本植物重金属抗性机制研究的良好试材。探索重金属在柳树根系的微区分布特征、赋存形态及其对根系耐性的影响，不仅可以丰富人们对木本植物重金属抗性机制的理论认识，而且有助于阐明木本植物在重金属污染土壤的定植与生存策略，为木本植物在植物修复工程中的应用提供参考。.本项目研究了杞柳不同栽培品种对铅的吸收、积累和分配特点以及根系在响应铅胁迫过程中的适应机制；采用组织化学方法和同步辐射技术分析了铅在杞柳体内的微区分布特征及化学形态。结果表明，铅抑制了杞柳地上部和根系的伸长生长，而促进了根系的径向生长；铅在杞柳不同组织中的积累量为：根>插条>枝条>叶，大部分铅积累于根部，极少向地上部转运。根系对不同性质重金属的吸收动力学存在差异，对铅的吸收为线性模型，而对锌的吸收则为Elovich模型。通过对铅在根部的组织化学定位发现，在根毛及根尖区，铅主要以点状或线状分布于近中柱区域，铅在进入主根以后，沿中柱区向地上部运输。SRXRF分析进一步证实，铅在根部主要分布在中柱。铅在杞柳体内的化学形态存在组织差异，在根部，大部分铅形成了难溶性的磷酸盐和草酸盐，一部分则与果胶或蛋白质吸附，使进入根系的铅大部分固定在根部；少部分形成水溶性复合物，运输到地上部。而在叶片，铅主要与果胶结合或以与蛋白质吸附的形态存在，少量铅与草酸结合，只有极少量的铅以水溶性化合物的形态存在。本研究明确了铅在杞柳体内的亚细胞分布和化学形态，阐明了细胞壁等非原生质体屏障以及果胶成分在杞柳根系铅耐性和积累过程中的作用，加深了对木本植物重金属抗性机制的了解。

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