稀土活化植物胞吞作用的靶分子及其机制探究

The wide application of rare earth elements has caused the accumulation of rare earth elements in ecosystem, including soil, atmosphere and water. The rapid development of rare earth industry and the wide application of rare earth elements have made it urgent to elucidate the cytobiological and cytochemical mechanisms of rare earth elements action on living organisms to ensure the quality and security of food, human health and environmental safety. However, the cellular mechanism remains unclear although scientists have extensively investigated the effect of rare earth ions upon cells since 1917. In the proposal, Arabidopsis (Arabidopsis thaliana L) and Ln(III)（Ln=La,Ce）which had been over accumulated in ecosystem will be chosen as a typical representative of the model plant and rare earth elements respectively. According to the results from our experiments in the project supported by Natural Science Foundation of China(20971069), here, we aim to reveal the mechanism and target molecules of Ln(III) activating endocytosis in the plant cells. In order to achieve the research purpose, these questions on which of molecules in the space between the cell wall and plasma membrane are given priority to coordinate Ln(III), how to activate the endocytosis of plasma membrane in plant, how to transfer signal, how to control the gene expression, how to regulate cytobiological responses and the growth of cells etc.,would be further investigated with optimizing combination of cytochemical means(EMARG etc.), computational chemistry(molecular dynamics simulation, quantum chemical calculation), cytobiological technique (FM, TIRFM, EWFM, LSCM etc.), molecular biology method (DN,CA etc.), and physicochemical technique (DPV, EXAFS, EPMA etc.). The results would provide some new thinking and references for scientifically assessing the damage of the accumulation of rare earth elements in biosystem to crop. They also would provide guide for establishing the international standard of rare earth elements limitation in plants and food.

以环境中累积量高的稀土离子[Ln(III),Ln=La、Ce]和模式植物拟南芥为典型代表；以揭示Ln(III)活化植物胞吞作用的靶分子及其机制为研究目的；以细胞化学(稀土放射自显影技术等)、计算化学(细胞环境分子动力学模拟及量化计算)、细胞生物学(细胞活体分子标记、全内反射荧光显微镜、隐失波荧光显微镜及激光扫描共聚焦显微镜等技术)、分子生物学(诱导突变体等技术)与物理化学(自主组装细胞电化学系统、近边X射线吸收精细结构、电子探针X射线微区分析等多种谱学技术)方法的优化组合为研究手段；以探究Ln(III)活化植物胞吞作用的靶分子-信号转导及途径(基因表达)-调控过程及细胞响应（生长）间关系为研究内容；阐明Ln(III)活化植物胞吞作用的首要靶分子、信号转导与调控过程、细胞响应及生长变化及其关系的机制，为从细胞及分子层次揭示稀土离子作用于植物的机理及其食品安全国际标准的建立提供借鉴。

植物在三十亿年演化过程中，叶细胞进化为胞吞惰性，以抵御外源有害物质经叶胞吞而进入生命体。 17种稀土元素[REE(III)]，除钷外，广存于自然界中，并进化为植物体共生的一类微量元素，已成不争之事实。项目以环境中累积量高的REE(III)(La、Ce及Tb)和模式植物拟南芥为代表，以稀土放射[140La(III)、141Ce(III)、160Tb(III)]电镜自显影技术、细胞及分子生物学、计算化学、物理化学等技术的优化组合为研究手段，获得重要结果：(1)低剂量REE(III)能打破叶细胞胞吞惰性的进化规则，借助其细胞质膜上阿拉伯半乳糖蛋白(AGPs)靶分子而启动叶细胞胞吞作用；REE(III)可在质膜酸性环境中与AGPs形成Lewis酸碱配合物而被AGPs锚定于叶细胞质膜上，使AGPs磷酸化(或作为AGPs的共同货物）而与衔接蛋白(AP2)结合，从而招募网格蛋白(Clathrin)至细胞质膜，启动Clathrin介导的AGP-AP2-Clathrin胞吞途径及其机制；随着AGP17-19基因表达的上调—叶细胞胞吞作用启动—叶细胞活性氧中超氧阴离子(O2˙-)和单线态氧(1O2)量增及胞吞信号的转导—根细胞胞吞作用的活化—植物特有的小G蛋白Rho家族中ROP2基因表达及其调控细胞极性生长能力增强—终引发植物整体正效应的响应机制；(2)随REE(III)在叶细胞质膜上累积量增加(尤其高浓度)，大量AGPs从细胞内招募到质膜上，叶和根细胞胞吞作用激增，除存在AGP-AP2-Clathrin胞吞途径及其机制外，同存在非Clathrin介导的胞吞途径及其机制；叶细胞中O2˙-和1O2量激增—根细胞胞吞活化的作用激增— ROP2调控的细胞极性生长被抑制—终呈现植物整体负效应响应的复杂机制，其中，叶细胞胞吞作用与环境中的污染因子(酸雨、重金属离子铅、双酚A)间，有协同胁迫植物细胞效应。在PNAS等SCI-top期刊上发表论文10篇；被Trends in Plant Science, Biomaterials， Chemical Reviews等引101次，部分成果被写入中国植物若干领域年度重要研究进展和国家自然科学基金委的基金要闻报道。这些研究结果，为从细胞及分子层次揭示REE(III)作用于植物的化学生物学机制，REE(III)在植物(尤其食品)中限量标准的建立，提供了借鉴。