植物重金属转运蛋白研究进展

土壤中的有毒重金属不仅对植物有害,也可通过食物链危害人类和动物的健康.重金属转运蛋白在植物吸收、抵抗重金属的复杂机制中起着关键作用.植物重金属转运蛋白分为吸收蛋白和排出蛋白,其中,吸收蛋白转运必需重金属进入细胞,同时也会因为必需重金属的缺乏或离子之间的竞争而运载有毒重金属;排出蛋白是一类解毒蛋白,可将过量的或有毒的重金属逆向转运出细胞,或区室化于液泡中.目前,细胞内多种重金属转运蛋白基因的转录水平与重金属离子积累之间的联系已被揭示,并分离克隆出诸多相关蛋白家族成员.本文综述了近年来发现并鉴定的主要重金属转运蛋白的金属亲和性、器官表达特异性及细胞内定位等的研究进展.     

超富集植物遏蓝菜对重金属吸收、运输和累积的机制

遏蓝菜Thlaspi caerulescens可以在其地上部累积大量重金属如锌、镉等,是公认的超富集植物。由于该植物生物量小,不宜直接用于重金属污染的土壤植物修复,而被广泛作为一种模式植物来进行重金属富集机制研究。遏蓝菜对重金属离子的累积大致经过螯合剂解毒、地上部长距离运输以及在液泡中的储存等生理过程。已经发现的植物体内的金属螯合剂——有机酸、氨基酸、植物络合素(PCs)、金属硫蛋白(MT)和尼克烟酰胺NA等,区室化以及长距离运输相关的转运蛋白——ZIP(ZRT/IRTlike protein)、CDF(Cation diffusion facilitator)、Nramp(Natural resistance and macrophage protein)和HMA(Heavy metal ATPase)等家族,以上各种基因、多肽与蛋白等共同参与了植物对金属累积与耐受过程并发挥各自重要的作用。以下主要介绍了遏蓝菜重金属超富集相关的基因、多肽和蛋白,以及它们在重金属螯合作用和运输过程中的功能。     

植物抗旱和耐重金属基因工程研究进展

干旱和重金属污染严重影响植物的生长发育.植物耐逆相关基因的克隆和功能鉴定研究,为通过基因工程途径提高植物的抗逆性奠定了理论基础.水分亏缺、高盐、低温和重金属胁迫都能诱导LEA(late embryogenesis abundant protein)基因的表达.转基因研究表明,LEA蛋白具有抗旱保护作用、离子结合特性以及抗氧化活性;水孔蛋白存在于细胞膜和液泡膜上,在细胞乃至整个植物体水分吸收和运输过程中发挥重要作用.干旱和盐胁迫促进水孔蛋白基因转录物的积累.过量表达水孔蛋白可增强水分吸收和运输,提高植物的抗旱能力.金属转运蛋白参与重金属离子的吸收、运输和累积等过程.这些蛋白基因在改良草坪草植物的抗旱节水和耐重金属能力等方面具有潜在的应用价值.     

超富集植物吸收富集重金属的生理和分子生物学机制

与普通植物相比,超富集植物在地上部富集大量重金属离子的情况下可以正常生长,其富集重金属的机理已经成为当前植物逆境生理研究的热点领域．尤其是近两年,随着分子生物学等现代技术手段的引人,关于重金属离子富集机理的研究取得了一定进展．通过与酵母突变株功能互补克隆到了多条编码微量元素转运蛋白的全长cDNA;也从分子水平上研究了谷胱甘肽、植物螯合素、金属硫蛋白、有机酸或氨基酸等含巯基物质与重金属富集之间的可能关系．本文从植物生理和分子生物学角度简要评述超富集植物对重金属元素的吸收、富集、整合及区室化的机制．     

植物对重金属的吸收和分布

植物修复是利用植物来清除污染土壤中重金属的一项技术。该技术成功与否取决于植物从土壤中吸取金属以及向地上部运输金属的能力。植物对金属的吸收主要取决于自由态离子活度。许多螯合剂能诱导植物对重金属的吸收。金属离子在液泡中的区域化分布是植物耐重金属的主要原因。同时,细胞内的金属硫蛋白、植物螯合脓等蛋白质以及有机酸、氨基酸等在金属贮存和解毒方面也起重要作用。本文还论述了重金属在植物体内运输的生理及分子方面的研究进展。     

植物对重金属的吸收和分布

植物修复是利用植物来清除污染土壤中重金属的一项技术。该技术成功与否取决于植 物从土壤中吸取金属以及向地上部运输金属的能力。植物对金属的吸收主要取决于自由态离子活度。许多螯合剂能诱导植物对重金属的吸收。金属离子在液泡中的区域化分布是植物耐 重金属的主要原因。同时,细胞内的金属硫蛋白、植物螯合肽等蛋白质以及有机酸、氨基酸等在金属贮存和解毒方面也起重要作用。本文还论述了重金属在植物体内运输的生理及分子 方面的研究进展。     

植物金属硫蛋白及其重金属解毒机制研究进展

金属硫蛋白是一类分子量较小、富含Cys的金属结合蛋白,广泛分布于生物界。近年来从植物中克隆到许多编码金属硫蛋白的基因,并在研究基因表达模式、组织表达特异性以及基因结构,如启动子、内含子在染色体上的定位等方面取得了一定进展,但对其功能的研究还处于起步阶段。很多实验表明,植物金属硫蛋白可以通过其大量的Cys残基螯合重金属并清除活性氧,使植物避免氧化损伤。文章介绍了植物金属硫蛋白的分类、特征、基因结构及其在植物重金属解毒中的作用。      

植物YSL家族基因研究进展

黄色条纹蛋白(Yellow stripe-like protein,YSL)是广泛存在于植物中的重金属吸收、转运蛋白,主要参与植物Fe~(3+)的吸收及对Fe~(2+)、Zn~(2+)、Cu~(2+)、Ni~(2+)和Mn~(2+)等金属离子的转运。目前,对于黄色条纹蛋白在植物体内的表达模式,亚细胞定位以及突变体等方面的研究揭示了其在植物生长发育过程中的作用。综述了近年来关于YSL基因在植物中的研究进展,旨为研究植物吸收铁的作用机理及生物强化谷物籽粒中的铁含量奠定基础。     

重金属污染土壤植物修复基本原理及强化措施探讨

阐述了植物修复的基本概念及主要作用方式 ,并从土壤中重金属存在形态 ,植物对重金属吸收、排泄和积累以及植物生物学特性与植物修复的关系等方面讨论了重金属污染土壤植物修复的基本原理及局限性和限制性因素 ,从超富集植物性能强化和技术强化两方面探讨了植物修复的强化措施 ,并指出与现代化农业技术相结合是植物修复重金属污染土壤大规模商业应用的一条捷径     

重金属污染环境的植物修复及其分子机制

重金属污染物的排放和扩散造成了日益严重的环境污染。如何消除环境中的重金属污染物已成为国际性难题。近年来,植物修复技术的出现和快速发展为我们展示了一条新的有效途径：即利用植物对重金属化合物的吸收、富集和转化能力去除土壤和水体中残存的重金属污染物。文章简要介绍了重金属污染物与植物修复的关系和植物修复的生理机制,重点总结了重金属污染环境的植物修复在分子生物学方面所取得的研究进展,包括有机汞裂解酶基因merB、汞离子还原酶基因merA和金属硫蛋白基因MT等的生物学功能及其在植物修复上的应用,展望了植物修复研究工作的发展方向,并针对汞污染提出了一套修复方案。     

Identification of Thlaspi caerulescens genes that may be involved in heavy metal hyperaccumulation and tolerance. Characterization of a novel heavy metal transporting ATPase

Thlaspi caerulescens is a heavy metal hyperaccumulator plant species that is able to accumulate extremely high levels of zinc (Zn) and cadmium (Cd) in its shoots (30,000 microg g(-1) Zn and 10,000 microg g(-1) Cd), and has been the subject of intense research as a model plant to gain a better understanding of the mechanisms of heavy metal hyperaccumulation and tolerance and as a source of genes for developing plant species better suited for the phytoremediation of metal-contaminated soils. In this study, we report on the results of a yeast (Saccharomyces cerevisae) complementation screen aimed at identifying candidate heavy metal tolerance genes in T. caerulescens. A number of Thlaspi genes that conferred Cd tolerance to yeast were identified, including possible metal-binding ligands from the metallothionein gene family, and a P-type ATPase that is a member of the P1B subfamily of purported heavy metal-translocating ATPases. A detailed characterization of the Thlaspi heavy metal ATPase, TcHMA4, demonstrated that it mediates yeast metal tolerance via active efflux of a number of different heavy metals (Cd, Zn, lead [Pb], and copper [Cu]) out of the cell. However, in T. caerulescens, based on differences in tissue-specific and metal-responsive expression of this transporter compared with its homolog in Arabidopsis (Arabidopsis thaliana), we suggest that it may not be involved in metal tolerance. Instead, we hypothesize that it may play a role in xylem loading of metals and thus could be a key player in the hyperaccumulation phenotype expressed in T. caerulescens. Additionally, evidence is presented showing that the C terminus of the TcHMA4 protein, which contains numerous possible heavy metal-binding His and Cys repeats residues, participates in heavy metal binding. When partial peptides from this C-terminal domain were expressed in yeast, they conferred an extremely high level of Cd tolerance and Cd hyperaccumulation. The possibilities for enhancing the metal tolerance and phytoremediation potential of higher plants via expression of these metal-binding peptides are also discussed.     

Molecular mechanisms of heavy metal hyperaccumulation and phytoremediation

A relatively small group of hyperaccumulator plants is capable of sequestering heavy metals in their shoot tissues at high concentrations. In recent years, major scientific progress has been made in understanding the physiological mechanisms of metal uptake and transport in these plants. However, relatively little is known about the molecular bases of hyperaccumulation. In this paper, current progresses on understanding cellular/molecular mechanisms of metal tolerance/hyperaccumulation by plants are reviewed. The major processes involved in hyperaccumulation of trace metals from the soil to the shoots by hyperaccumulators include: (a) bioactivation of metals in the rhizosphere through root–microbe interaction; (b) enhanced uptake by metal transporters in the plasma membranes; (c) detoxification of metals by distributing to the apoplasts like binding to cell walls and chelation of metals in the cytoplasm with various ligands, such as phytochelatins, metallothioneins, metal-binding proteins; (d) sequestration of metals into the vacuole by tonoplast-located transporters. The growing application of molecular-genetic technologies led to the well understanding of mechanisms of heavy metal tolerance/accumulation in plants, and subsequently many transgenic plants with increased resistance and uptake of heavy metals were developed for the purpose of phytoremediation. Once the rate-limiting steps for uptake, translocation, and detoxification of metals in hyperaccumulating plants are identified, more informed construction of transgenic plants would result in improved applicability of the phytoremediation technology.     

Investigation of heavy metal hyperaccumulation at the cellular level: development and characterization of Thlaspi caerulescens suspension cell lines

The ability of Thlaspi caerulescens, a zinc (Zn)/cadmium (Cd) hyperaccumulator, to accumulate extremely high foliar concentrations of toxic heavy metals requires coordination of uptake, transport, and sequestration to avoid damage to the photosynthetic machinery. The study of these metal hyperaccumulation processes at the cellular level in T. caerulescens has been hampered by the lack of a cellular system that mimics the whole plant, is easily transformable, and competent for longer term studies. Therefore, to better understand the contribution of the cellular physiology and molecular biology to Zn/Cd hyperaccumulation in the intact plant, T. caerulescens suspension cell lines were developed. Differences in cellular metal tolerance and accumulation between the cell lines of T. caerulescens and the related nonhyperaccumulator, Arabidopsis (Arabidopsis thaliana), were examined. A number of Zn/Cd transport-related differences between T. caerulescens and Arabidopsis cell lines were identified that also are seen in the whole plant. T. caerulescens suspension cell lines exhibited: (1) higher growth requirements for Zn; (2) much greater Zn and Cd tolerance; (3) enhanced expression of specific metal transport-related genes; and (4) significant differences in metal fluxes compared with Arabidopsis. One interesting feature exhibited by the T. caerulescens cell lines was that they accumulated less Zn and Cd than the Arabidopsis cell lines, most likely due to a greater metal efflux. This finding suggests that the T. caerulescens suspension cells represent cells of the Zn/Cd transport pathway between the root epidermis and leaf. We also show it is possible to stably transform T. caerulescens suspension cells, which will allow us to alter the expression of candidate hyperaccumulation genes and thus dissect the molecular and physiological processes underlying metal hyperaccumulation in T. caerulescens.     

超富集植物对重金属耐受和富集机制的研究进展

超富集植物对重金属耐受和富集机制的研究成为近年来植物逆境生理研究的热点,在简要总结细胞壁沉淀、重金属螯合效应、酶活性机制和细胞区室化作用的基础上,概述了超富集植物对重金属的耐受机制,讨论了重金属跨根细胞质膜运输,共质体内运输、木质部运输和跨叶细胞膜运输的富集过程。     

Increase of glutathione in mine population of Sedum alfredii: a Zn hyperaccumulator and Pb accumulator

Phytochelatins (PCs) have been induced in a large range of plant species, but their role in heavy metal tolerance is unclear. Sedum alfredii is a new zinc (Zn) hyperaccumulator and lead (Pb) accumulator found in an old Pb/Zn mine in the Zhejiang Province of China. Until now, the mechanisms of its hyperaccumulation/accumulation and tolerance were poorly understood. The aim of this work was to investigate whether PCs were differentially produced in mine populations of S. alfredii compared with a non-mine control of the same species. The results showed that plants from the mine site were more tolerant to increasing Zn and Pb concentrations than those from the control site. No PCs and cysteine (Cys) were detected by pre-column derivatization with HPLC fluorescence in any tissues of two populations at any treatment, which in turn indicated they were not responsible for Zn and Pb tolerance in the mine population. Instead, Zn and Pb treatments resulted in the increase of glutathione (GSH) for both populations in a tissue-dependent manner. Significant increases were observed in leaf, stem and root tissues of plants grown on the mine site. The results suggest that GSH, rather man PCs, may be involved in Zn and Pb transport, hyperaccumulation/accumulation and tolerance in mine population of S. alfredii.     

Root-to-shoot long-distance circulation of nicotianamine and nicotianamine-nickel chelates in the metal hyperaccumulator Thlaspi caerulescens

Plant metal hyperaccumulator species are widely used as models to unravel the heavy metal tolerance and hyperaccumulation mechanisms. Thlaspi caerulescens is capable of tolerating and hyperaccumulating Zn, Cd, and Ni. A search for factors involved in the cellular tolerance to Ni, based on yeast screens, led to isolation of a cDNA encoding a functional nicotianamine (NA) synthase (NAS). The T. caerulescens genome appears to contain a single copy of the NAS gene named TcNAS whose expression is restricted to the leaves. The analysis of dose-response and time-course Ni treatments have revealed that the exposure to Ni triggers the accumulation of NA in the roots. Because neither TcNAS expression nor NAS activity were detected in the roots, the NA accumulation in roots is most probably the result of its translocation from the leaves. Once in the roots, NA, together with Ni, is subsequently found in the xylem, for redirection to the aerial parts. Using liquid chromatography coupled to inductively coupled plasma or electrospray ionization mass spectrometry, it has been shown that part of the Ni is translocated as a stable Ni-NA complex in the xylem sap. This circulation of NA, Ni, and NA-Ni chelates is absent in the non-tolerant non-hyperaccumulator related species T. arvense. Taken together, the results provide direct physiological and chemical evidence for NA and NA-heavy metal complex translocation in a hyperaccumulator species.     

Intraspecific variation of metal preference patterns for hyperaccumulation in Thlaspi caerulescens: evidence from binary metal exposures

Metal preferences with regard to accumulation were compared between populations of the heavy metal hyperaccumulator Thlaspi caerulescens, originating from calamine, serpentine and non-metalliferous soils. Plants were exposed for 3 weeks to factorial combinations of concentrations of different metals in binary mixture in hydroponics. The nature and degree of the interactions varied significantly between populations. In the calamine, non-Cd/Ni-hyperaccumulating population, La Calamine, there were no one-sided or mutual antagonistic interactions among the metals with regard to their accumulation in the plant. In three other populations capable of Cd and Ni hyperaccumulation, from calamine, serpentine and non-metalliferous soil respectively, there were one-sided or mutual antagonistic interactions between Cd and Zn, Cd and Ni, and Ni and Zn, possibly resulting from competition for transporters involved in uptake or plant-internal transport. Significant synergistic interactions, probably resulting from regulation of transporter expression, were also found, particularly in the La Calamine population. All the populations seemed to express a more or less Zn-specific high-affinity system. The serpentine and the non-metallicolous populations seemed to posses low-affinity systems with a preference for Cd and Zn over Ni, one of which may be responsible for the Ni hyperaccumulation of the serpentine population in its natural environment. The calamine population from Ganges also seemed to express a strongly Cd-specific high-affinity system which is in part responsible for the Cd-hyperaccumulation phenotype exhibited by this population in its natural environment.     

基因工程改良植物重金属抗性与富集能力的研究进展

基于分子水平上对植物吸收、解毒、忍耐以及超富集重金属的几个关键步骤的认识,以及一些功能基因相继在细菌、酵母、植物和动物中被分离、鉴定,近年来,人们利用转基因技术提高植物重金属抗性和富集能力方面已获得进展, 一些功能基因（如gsh1, MerA和ArsC)及其工程植物已显示出植物修复产业化潜力。特别对转基因技术所采取的分子生物学途径、达到的效果以及存在的问题进行了详述,对今后研究的重点和策略进行了探讨。     

高等植物重金属耐性与超积累特性及其分子机理研究

由于重金属污染日益严重, 重金属在土壤_植物系统中的行为引起了人们的高度重视。高等植物对重金 属的耐性与积累性, 已经成为污染生态学研究的热点。近年来, 由于分子生态学等学科的发展, 有关植物对重金属的解毒和耐性机理、重金属离子富集机制的研究取得了较大进展。高等植物对重金属的耐性和积累在种间和基因型之间存在很大差异。根系是重金 属等土壤污染物进入植物的门户。根系分泌物改变重金属的生物有效性和毒性, 并在植物吸收重金属的过程中发挥重要作用。土壤中的大部分重金属离子都是通过金属转运蛋白进入根细胞, 并在植物体内进一步转运至液泡贮存。在重金属胁迫条件下植物螯合肽 (PC) 的合成是植物对胁迫的一种适应性反应。耐性基因型合成较多的PC, 谷胱甘肽 (GSH) 是合成PC的前体, 重金属与PC螯合并转移至液泡中贮存, 从而达到解毒效果。金属硫蛋白 (MTs) 与PC一样, 可以与重金属离子螯合, 从而降低重金属离子的毒性。该文从分子水平上论述了根系分泌物、金属转运蛋白、MTs、PC、GSH在重金属耐性及超积累性中的作用, 评述了近 10年来这方面的研究进展, 并在此基础上提出存在的问题和今后研究的重点。