盐肤木根系细胞壁果胶修饰对质外体空间铅分布的影响

As a widespread potential environmental pollutant, lead has been widely concerned. Phytoremediation is referred to using plants and associated soil microbes to reduce concentrations of heavy metals in soils. However, the mechanism of heavy metal uptake and transport of heavy metal in woody plants was unknown. Our previous study showed that Rhus chinensis might have the potential for effective phytoextraction of Pb, and most of the Pb in the R. Chinensis tissues was stored in the cell wall. In addition, the ratio of NaCl-extractable form of the tissues was increased under Pb stress. Therefore, we speculate that pectin plays an important role in the accumulation of Pb. Here, we employed a combination of stable isotopic tracer techniques, tissue staining and ion group method to identify the contribution of the apoplast pathway of absorption and transport in Pb. On this basis, to clarify the impact of the apoplasmic pathway on translocation of Pb to the xylem in roots of R. chinensis, the effects of the distribution of lead in apoplasmic spatial by composition and pectin modification of cell wall was studied. At the same time, based on the analysis of transcriptome data of pectin modification and reconstruction of cell wall, the mechanism of molecular regulation of apoplasmic pathway in Pb uptake and translocation was constructed. The results can help to reveal physiological and molecular mechanisms of heavy metal accumulation in woody plants, and provide scientific basis for breeding and screening efficient, ideal hyperaccumulator plants and improving the efficiency of phytoremediation technology.

铅作为一种广泛存在的环境污染物已经得到广泛关注。植物修复是具有前景的重金属污染土壤修复方法。但目前对木本植物吸收转运铅的机理认识仍然不足。前期研究发现盐肤木对铅有较好的吸收转运能力，细胞壁是铅主要积累位点，并且铅胁迫下氯化钠提取态铅所占比例增加。据此我们推测盐肤木根系细胞壁果胶在铅高积累过程中发挥了重要作用。为验证这一假说，本项目利用稳定同位素示踪技术、组织荧光染色技术，并结合离子组学方法，明确质外体途径在铅吸收转运中的贡献。在此基础上，重点围绕质外体空间细胞壁组成与修饰对质外体空间铅分布的影响开展研究，阐明质外体途径在盐肤木吸收及转运中的作用。同时结合铅诱导根细胞壁果胶修饰和重构的转录组数据分析，构建质外体途径在盐肤木铅吸收运输中的分子调控机制。研究结果有助于揭示木本植物重金属积累的生理及分子机理，为培育和筛选高效、理想的超积累植物，提高植物修复效率提供科学依据。

植物修复技术是一种新型、经济和绿色的修复技术。盐肤木生长迅速、生物量大、分布范围广、适应能力强，是铅污染土壤修复的良好植物资源。本项目以盐肤木为对象，利用组织荧光染色技术，并结合离子组学方法，明确质外体途径在铅吸收转运中的贡献。在此基础上，重点围绕质外体空间细胞壁组成与修饰对质外体空间铅分布的影响开展研究，阐明质外体途径在盐肤木吸收及转运中的作用。同时结合铅诱导根细胞壁果胶修饰和重构的转录组数据分析，构建质外体途径在盐肤木铅吸收运输中的分子调控机制。主要研究结果如下：. 试验表明在铅处理下，质外体途径是盐肤木铅积累的主导影响因子。不同生态型盐肤木具有相同的铅吸收途径，且质外体途径贡献率均在75%以上。利用SIET技术发现盐肤木铅离子流速由根尖向根基的方向逐渐降低，染色和LA-ICP-MS技术发现铅在中柱中只有少量沉积，说明铅离子很难从皮层转移到木质部。. 铅胁迫下盐肤木根系果胶含量和果胶甲酯酶活性增加，且果胶甲酯酶活性增加幅度大于果胶含量。导致果胶甲酯化度降低，从而暴露出大量的自由羧基用来结合铅离子，使其固定在细胞壁上，从而减少铅的毒害。同时铅胁迫条件下，盐肤木根系较高的质外体pH，与其铅胁迫下维持较高的H+内流有关，两者同时受到质膜H+-ATPase的调控。铅胁迫下，盐肤木可通过增加果胶甲酯酶活性和相关基因PEM3等的表达水平，降低果胶甲酯化度降，增强了铅在细胞壁上的螯合作用。

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