稀土元素在植物中的分异研究进展

有关对稀土农用的理论和实践、天然和农业生态系统中稀土的地球化学行为及稀土的增产生理过程与毒理等方面已开展了大量研究,而对稀土进入植物体内的迁移过程、分布分异现象和机制缺乏必要的了解。稀土元素在植物中的分异研究有助于“示踪”稀土元素在土壤(溶液)-植物系统中的迁移路径,进而查明控制稀土元素迁移和积累的体外和体内敏感因素。本文结合近5年的研究工作,就近年来国内外有关稀土元素在植物中的分异现象、机制及其研究意义进行了综述,并展望了此方面的研究趋势,期望能为稀土以及重金属的生物有效性研究开辟一条新思路。     

中子活化法研究稀土矿区植物体中稀土元素的分布特征

用仪器中子活化法测定了我国江西赣南某离子吸附型稀土矿区生长的１７种不同植物中８个稀土元素的含 研究了稀土元素在植物体内的分布特征。结果表明，称土矿区植物体内的稀土元素含量较高，其中铁芒萁叶中部属然土含一可达３０００μｇ／ｇ以上，比其它植物叶高２－３个数量级。植物体各部位的稀土含量分布一般为根〉叶〉茎。经球粒陨石归一化后，稀土元素分布模式均与其母土基本相似。然而，在植物从土壤吸收及输送的吕，稀土元素     

土壤-植物体系稀土元素的分异现象

用仪器中子活化分析测定了从同一地点采集的9种不同植物根和叶中8个稀土元素（La,Ce,Nd,Sm,Eu,Tb,Yb和Lu)的含量，研究了稀土元素在植物根、叶及相应母土中的分布特征。结果表明，同一植物的根、叶和母土中稀土分布模式均有较大差异。生长在同一地点不同植物根中稀土分布模式非常相似，而叶中分布规模差别较明显。说明根对单一稀土元素的吸收主要取决于这个元素在土壤中有效态的含量，而在稀土从根到叶的运输和积累过程中出现的分异则由植物自身的结构特征决定。     

土壤的植物修复与超积累植物研究

被污染土壤的植物修复将是未来更好与更廉价的修复技术,所以近年来对植物修复与超积累植物的研究兴趣日益增加。本文简要介绍了近期的发展趋势。目前研究的重点包括根际土壤微环境中的复杂反应与吸收过程,金属从土壤向植物根以及从植物根向叶的传输过程,金属在超积累植物中的定位与螯合作用等等。这是分析化学与环境科学及植物科学交叉研究的新领域,充满挑战。     

超积累植物体内的小分子螯合物质及其生理作用

螯合效应是超积累植物忍耐重金属的重要机理之一,不同的超积累植物对不同的重金属胁迫其体内产生的螯合物质不同。目前在超积累植物中发现的螯合物质以其分子量大小可分为两大类,即：草酸、组氨酸、苹果硫、柠檬酸及谷胱甘肽等小分子物质和金属硫蛋白、植物络合素、金属结合体及金属结合蛋白等大分子物质。本文就超积累植物体内的小分子螯合物质及其生理作用作一概述。     

土壤稀土元素和氮化物污染对植物生长及生理的影响

近年来,对稀土矿区土壤污染的修复成为中国关注的热点之一。稀土矿区存在的污染物主要是稀土元素与氮化物,本文在概述稀土元素在中国的分布及污染现状的基础上,综述了稀土元素、氮化物分别对植物生长的影响及其可能的生理生化机制,以及稀土元素-氮化物共存时对植物生长的影响,并提出了未来需要加强对稀土元素及养分元素复合污染的研究以及内外源稀土对植物生长的差异性研究。     

稀土元素防治植物病害的研究进展

稀土元素在农业上应用的有关研究主要集中在植物生理活性、生理生化机制及稀土元素的卫生毒理学和环境安全性方面，对其在防治植物病害、对植物病原微生物方面的研究较少。本文对稀土元素在防治植物病害及诱导植物抗病性方面进行了综述，重点探讨了稀土元素防治植物病害的作用机制，并展望了此方面的应用前景，期望能够对于进一步研究利用稀土防治植物病害。拓宽稀土元素农用范围发挥一定的指导作用。     

稀土生物功能-植物＆微生物篇

稀土及其化合物早已被广泛应用于农业和医药业等生产实践中，多年的稀土生物无机化学研究表明：稀土元素能够增强植物光合作用，促进根系吸收，调节激素和氮代谢，抑制细菌繁殖等。稀土能够选择生物代谢中关键的生物分子的靶位点进行结合或取代反应，调控生物分子的功能和行为。从而在植物和微生物体内发挥了重要的生物学功能。然而，过量的稀土会对机体的生长带来不利的影响，为了在生产实践中更加科学和安全地应用稀土的生物功能，稀土最适剂量的探究及其在生物体内积累效应的研究将会是下个阶段的研究重点。     

金属有机配体分析方法及金属组学研究

环境和生物样品中金属与有机酸、氨基酸、多糖、蛋白质、DNA等形成的金属有机物是一系列生物金属。生物金属中参与金属离子配位的有机配基主要是含氧、硫、氮及磷的功能团。金属组学是整合生物金属中金属有机配体的结合形态及其生理功能活性的新概念。文中介绍了目前常用的金属有机配体的分析方法以及金属组学领域的研究技术,并展望了重金属富集和超积累植物的研究前景。     

不同吸附剂对稀土离子的吸附特性研究进展

稀土元素在环境中的迁移与积累、稀土元素的高效提取与分离和各种有机或无机物质对稀土元素的吸附特性息息相关,故研究稀土元素在不同吸附剂中的吸附和解吸特性具有重要意义。在归纳经典的等温吸附模式、动力学和热力学方程的基础上,对近年来土壤、不同生物质及其他吸附剂对稀土元素的吸附特性进行了总结,阐述了土壤吸附对环境中稀土元素分布、迁移和转化的影响及作用,分析了不同生物质及其他吸附剂对稀土吸附的等温吸附模式及影响因素,指出了其在稀土元素分离以及治理稀土离子污染等领域的应用,对稀土元素吸附特性下一步研究进行了展望,使人们对该领域有更加全面的了解。     

Subcellular and molecular localization of rare earth elements and structural characterization of yttrium bound chlorophyll a in naturally grown fern Dicranopteris dichotoma

A rare earth element (REE) hyperaccumulator, Dicranopteris dichotoma, sampled from an REE mining area in South-Jiangxi region, was chosen for analysis of 15 REEs at subcellular and molecular levels by inductively coupled plasma-mass spectrometry (ICP-MS). The sum of the concentrations of 15 REEs (∑REEs) of D. dichotoma leaf was about 0.1% dry mass. Results indicated that the ∑REEs of different subcellular fractions of D. dichotoma leaf were cell walls>organelles>the ‘soluble’ fraction (i.e., cytosol and vacuoles)>cell membranes. ICP-MS results also showed that REEs existed in chlorophylls and lutein, though REE concentrations in carotene and pheophytin were both lower than the procedural blank levels. The ∑REEs of crude lipopolysaccharide and Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) obtained from D. dichotoma leaf were 1200 and 343 mg/kg, respectively. The extended X-ray absorption fine structure (EXAFS) study of D. dichotoma chlorophyll a indicated that yttrium was bound to the porphyrin ring of chlorophyll a, and one yttrium atom was surrounded by four nitrogen atoms with the average yttrium-nitrogen bond length being 0.236 nm. These data might be useful for understanding of the physiological role of REEs in hyperaccumulator D. dichotoma.     

Distribution of rare earth elements among chloroplast components of hyperaccumulator<Emphasis Type="Italic"> Dicranopteris dichotoma</Emphasis>

A rare earth element (REE) hyperaccumulator, Dicranopteris dichotoma, that accumulates more than 0.1% REEs dry leaf mass has been discovered in southern China. The different components of chloroplast were isolated and the concentration of REEs in each component was determined by ICP-MS. The experimental data indicated that about 8% of total leaf REEs was present in the chloroplast of Dicranopteris dichotoma. In order to thoroughly study the distribution of REEs among different components of chloroplast, the membrane of chloroplast, the intact thylakoid and the photosystem II (PS II system) of D. dichotoma were isolated from the chloroplast. It was found that half of total chloroplast REEs was stored at the membrane of the chloroplast and another half was in the thylakoid. And 25% of total chloroplast REEs was bound with PS II system of D.dichotoma. The concentration of REEs in chlorophyll a was only at the level of g/g on the bases of chlorophylls. These data are useful for understanding of both the storage of REEs in chloroplast and the effect of REEs on the photosynthesis of plants.     

Subcellular distribution of rare earth elements and characterization of their binding species in a newly discovered hyperaccumulator Pronephrium simplex

Subcellular distribution of rare earth elements (REEs, including 14 lanthanides and yttrium) in a newly discovered REE hyperaccumulator, Pronephrium simplex (P. simplex), was determined by a chemical sequence extraction followed by ICP-MS analysis. Results showed that most REEs are associated with cell wall and proteins, and REEs concentration in the proteins, 2899.5 μg g⁻¹, is much higher than those in the cell wall; in the chloroplast of P. simplex, REEs distribute almost equally in chloroplast membrane and thylakoid, while most REEs in the thylakoid are binding with photosystem II (PS II); a new REE-binding peptide in the lamina of P. simplex, which can accumulate REEs up to 3000 μg g⁻¹ and has higher affinity with light REEs, was characterized, indicating that its molecular mass is 5073 Da, and may have β-sheet structure; isoelectrofocusing electrophoretic photograph indicated that it is acidic peptide with IP of 3.7. Such information should be useful for understanding of both the storage and physiological role of REEs in P. simplex and further studies on the phytoremediation of REEs contaminated environments.     

Determination of rare earth elements in carbonatites from the Kangankunde Mine, Malawi by instrumental neutron activation analysis

Nine rare earth elements (REEs) in African carbonatite samples were determined by instrumental neutron activation analysis (INAA). The geochemical behavior of REEs in carbonatites, especially REE pattern (chondrite-normalized), is studied in relation to carbonatite formation at the Kangankunde Mine, Malawi. REE-rich phosphate minerals, particularly monazite, and the other unusual minerals such as strontianite, are observed during the stages of carbonatite formation. Four kinds of carbonatites exhibit similar chondrite-normalized REE distribution patterns in spite of the marked difference of their REE contents. All these carbonatites are characterized by the strong fractionation between light and heavy REEs and by the very high La/Yb ratio (1000-2800).     

Efficient recovery of rare earth elements from coal based resources: a bioleaching approach

Rare earth element (REE) resources in coal-related materials are vast. Assuming a coal production rate of 600 million short tons per year with an average REE content of 200 ppm, the potential REE resource is 120,000 tons per year, which is similar to the annual global production of REEs. Most of those resources that are associated with coal-related materials are found in association with the gangue or ash-based content from the coal ore. Under normal coal plant operation, the REEs often end up in refuse piles or tailings impoundments. In many cases, these REEs can be recovered at low cost using appropriate coal preparation, heap leaching, solvent extraction and/or selective precipitation, followed by subsequent separation and purification of individual REEs. In the present research, the processing approach uses a natural pyrite stream, which was removed during coal cleaning and used to enhance leaching. Bio-oxidation has been used commercially to accelerate leaching, and this approach has been applied to coal-based materials. The ferric ions generated from bio-oxidation oxidize sulfide minerals such as pyrite, which generates acid. Both acid and ferric ions are helpful for leaching REEs, as well as for removing residual sulfides, thereby preventing future acid mine drainage and related liabilities. It can be seen that, recovery of REEs from coal waste materials can enable coal producers to use untapped REEs resources to produce revenue and extend resource life while simultaneously reducing future environmental issues and costs.     

电感耦合等离子体质谱(ICP-MS)法测定高钨基体样品中稀土元素的含量

准确测定钨矿和钨酸盐晶体等高钨基体样品中稀土元素的含量有助于开展矿床地球化学特征研究及钨酸盐激光晶体材料的制备和性质研究。在高钨基体样品电感耦合等离子体质谱法（ICP-MS）分析时,为了考察高钨及高含量阳离子等基体组成对分析结果的影响,实验针对Na2WO4、CaWO4、NaY(WO4)2、MnWO4和(Fe,Mn)WO4等高钨基体样品,采用硝酸和氢氟酸高压密闭消解,加入稀土元素并用2% HNO3溶液稀释定容配制成稀土元素浓度为1 ng·g-1的基体匹配标准溶液;同时,直接用2% HNO3溶液配制稀土元素浓度相同的非基体匹配标准溶液以对比系统考察两种基体溶液中稀土元素的相对灵敏度系数（RSC）差异。结果显示,基体匹配溶液与2% HNO3溶液中稀土元素的RSC相对偏差基本小于15%,表明基体效应的影响可以忽略不计。进而,为了准确测定常见高钨基体样品中稀土元素的含量,实验建立了基于ICP-MS的高钨基体样品中稀土元素准确定量分析方法,该方法线性关系好（R2 ? 0.9997）,检出限低（0.5 ~ 27.9 pg·g-1）,准确度理想（相对误差-6.25 ~ 10.74%）。采用该方法测定了钨酸钙单晶实际样品中稀土元素的含量并将其与基体匹配法的测定结果进行比对,结果显示两者相对偏差为0.80 ~ 12.75%,说明本文所建立的分析方法可靠,能用于定量测定高钨基体样品中稀土元素的含量。     

Determination of rare-earth elements by high-performance liquid chromatography/inductively-coupled plasma/atomic emission spectrometry

Liquid chromatography coupled on-line to a sequential ICP/AES system is applied for the determination of 14 rare-earth elements (REEs) in samples with widely different concentrations of REEs and matrix elements. The REEs are separated on a cation-exchanger by applying an α- hydroxyisobutyric acid gradient. The determination limits were the same as those obtained by continuous nebulization of single-element standard solutions. The chromatographic separation precludes mutual spectral interferences between the REEs. The practical value of the method developed is demonstrated by the determination of REE impurities in Specpure rare-earth oxides, by its demonstrated potential to evaluate real spectral interferences, and by the analysis of geological samples (natural phosphates) with relatively low total REE contents. The detection limits of REEs in these natural phosphates ranged between 0.005 and 0.4 μg g^?1.     

稀土元素在植物中的分异机制 (I) 小麦不同器官中的稀土元素分异模式及形成机制

以小麦为植物材料，利用外源稀土添加、营养液培养等人工控制手段，研究了稀土元素在植物体内的分异效应，并探讨了分异效应产生的机制。结果表明，稀土元素在小麦不同器官中出现显著分异。根系出现中稀土(MREE)富集特征和“M”型四重效应，分析是由稀土元素与PO4^3-的选择性沉淀造成。小麦地上部分稀土元素分布出现“W”型四重效应，分析也是由根部磷沉淀造成。与此同时，小麦茎部相对富集轻稀土(LREE)，叶中相对富集重稀土(HREE)。运用VMINTEQ程序计算了木质部溶液中稀土元素的结合形态主要有LnEDTA^-和Ln^3 (Ln指稀土元素)，但仅有LnEDTA^-表现出HREE相对富集特征，其他形态则表现出LREE相对富集特征。分析叶部LREE／HREE分异是吸收LnEDTA^-造成，而茎部LREE／HREE分异则是吸收Ln^3 和其他形态稀土的结果。细胞壁对Ln^3 的吸附也是导致以上分异特征的重要因素。     

稀土元素日允许摄入量与农用安全性探讨

稀土农用是我国独立开创的稀土应用领域,30年来,取得了巨大的经济效益。然而,作为元素周期表中第ⅢB主族的重金属,稀土元素不是动植物的必需微量元素,其生理效应的机制还不清楚,稀土农用的安全性问题一直受到密切的关注。本文从稀土元素分析方法与人均总膳食摄入量、稀土元素毒理实验方法与日允许摄入量、稀土农用对土壤中稀土元素含量和化学形态的影响、以及稀土农用对食物中稀土元素含量影响的4个方面,对文献报道作了分析、整理和评定,结论是只要对使用的范围、剂量及施用方式进行限制,稀土农用是一种安全的农业增产方式。