高等植物铁元素的吸收、转位和调控

铁(Fe)是大多数生物体必需的微量营养元素.虽然铁在许多土壤中是丰富的,但铁在土壤中的可溶性非常低,常常限制植物生长.此外,铁自身存在高度的氧化还原特性,对细胞具有潜在的毒性.因此,细胞内铁的动态平衡需要严格调控.植物细胞中形成了一个复杂的信号网络来调节对铁的摄取、分配、运输及其代谢等过程.非禾本科和禾本科植物物种分别通过基于铁还原和铁螯合的两种不同策略从土壤中获得铁.植物对铁的吸收受到局部和全身信号的调控.系统信号通路似乎整合了激素信号、一氧化氮(NO)信号和植物营养需求等多种因素.综述了两种策略所依赖的分子机制和在铁缺乏条件下负责诱导这些策略的因素.     

Photochemical cycling of iron in the surface ocean mediated by microbial iron(III)-binding ligands

Iron is a limiting nutrient for primary production in large areas of the oceans. Dissolved iron(III) in the upper oceans occurs almost entirely in the form of complexes with strong organic ligands presumed to be of biological origin. Although the importance of organic ligands to aquatic iron cycling is becoming clear, the mechanism by which they are involved in this process remains uncertain. Here we report observations of photochemical reactions involving Fe(III) bound to siderophores--high-affinity iron(III) ligands produced by bacteria to facilitate iron acquisition. We show that photolysis of Fe(III)-siderophore complexes leads to the formation of lower-affinity Fe(III) ligands and the reduction of Fe(III), increasing the availability of siderophore-bound iron for uptake by planktonic assemblages. These photochemical reactions are mediated by the alpha-hydroxy acid moiety, a group which has generally been found to be present in the marine siderophores that have been characterized. We suggest that Fe(III)-binding ligands can enhance the photolytic production of reactive iron species in the euphotic zone and so influence iron availability in aquatic systems.     

The type IV mucolipidosis-associated protein TRPML1 is an endolysosomal iron release channel

TRPML1 (mucolipin 1, also known as MCOLN1) is predicted to be an intracellular late endosomal and lysosomal ion channel protein that belongs to the mucolipin subfamily of transient receptor potential (TRP) proteins. Mutations in the human TRPML1 gene cause mucolipidosis type IV disease (ML4). ML4 patients have motor impairment, mental retardation, retinal degeneration and iron-deficiency anaemia. Because aberrant iron metabolism may cause neural and retinal degeneration, it may be a primary cause of ML4 phenotypes. In most mammalian cells, release of iron from endosomes and lysosomes after iron uptake by endocytosis of Fe(3+)-bound transferrin receptors, or after lysosomal degradation of ferritin-iron complexes and autophagic ingestion of iron-containing macromolecules, is the chief source of cellular iron. The divalent metal transporter protein DMT1 (also known as SLC11A2) is the only endosomal Fe(2+) transporter known at present and it is highly expressed in erythroid precursors. Genetic studies, however, suggest the existence of a DMT1-independent endosomal and lysosomal Fe(2+) transport protein. By measuring radiolabelled iron uptake, by monitoring the levels of cytosolic and intralysosomal iron and by directly patch-clamping the late endosomal and lysosomal membrane, here we show that TRPML1 functions as a Fe(2+) permeable channel in late endosomes and lysosomes. ML4 mutations are shown to impair the ability of TRPML1 to permeate Fe(2+) at varying degrees, which correlate well with the disease severity. A comparison of TRPML1(-/- )ML4 and control human skin fibroblasts showed a reduction in cytosolic Fe(2+) levels, an increase in intralysosomal Fe(2+) levels and an accumulation of lipofuscin-like molecules in TRPML1(-/-) cells. We propose that TRPML1 mediates a mechanism by which Fe(2+) is released from late endosomes and lysosomes. Our results indicate that impaired iron transport may contribute to both haematological and degenerative symptoms of ML4 patients.     

Availability and toxicity of Fe(II) and Fe(III) in Caco-2 cells

The objective of the present study was to compare the toxicity and availability of Fe(II) and Fe(III) to Caco-2 cells. Cellular damage was studied by measuring cell proliferation and lactate dehydrogenase (LDH) release. The activities of two major antioxidative enzymes [superoxide dismutase (SOD) and glutathione peroxidase (GPx)] and differentiation marker (alkaline phosphatase) were determined after the cells were exposed to different levels of iron salts. The cellular iron concentration was investigated to evaluate iron bioavailability. The results show that iron uptake of the cells treated with Fe(II) is significantly higher than that of the cells treated with Fe(III) (P<0.05). Fe(II) at a concentration >1.5 mmol/L was found to be more effective in reducing cellular viability than Fe(III). LDH release investigation suggests that Fe(II) can reduce stability of the cell membrane. The activities of SOD and GPx of the cells treated with Fe(II) were higher than those of the cells treated with Fe(III), although both of them increased with raising iron supply levels. The results indicate that both Fe(II) and Fe(III) could reduce the cellular antioxidase gene expression at high levels.     

Structure and reactivity of a mononuclear non-haem iron(III)-peroxo complex

Oxygen-containing mononuclear iron species--iron(III)-peroxo, iron(III)-hydroperoxo and iron(IV)-oxo--are key intermediates in the catalytic activation of dioxygen by iron-containing metalloenzymes. It has been difficult to generate synthetic analogues of these three active iron-oxygen species in identical host complexes, which is necessary to elucidate changes to the structure of the iron centre during catalysis and the factors that control their chemical reactivities with substrates. Here we report the high-resolution crystal structure of a mononuclear non-haem side-on iron(III)-peroxo complex, [Fe(III)(TMC)(OO)](+). We also report a series of chemical reactions in which this iron(III)-peroxo complex is cleanly converted to the iron(III)-hydroperoxo complex, [Fe(III)(TMC)(OOH)](2+), via a short-lived intermediate on protonation. This iron(III)-hydroperoxo complex then cleanly converts to the ferryl complex, [Fe(IV)(TMC)(O)](2+), via homolytic O-O bond cleavage of the iron(III)-hydroperoxo species. All three of these iron species--the three most biologically relevant iron-oxygen intermediates--have been spectroscopically characterized; we note that they have been obtained using a simple macrocyclic ligand. We have performed relative reactivity studies on these three iron species which reveal that the iron(III)-hydroperoxo complex is the most reactive of the three in the deformylation of aldehydes and that it has a similar reactivity to the iron(IV)-oxo complex in C-H bond activation of alkylaromatics. These reactivity results demonstrate that iron(III)-hydroperoxo species are viable oxidants in both nucleophilic and electrophilic reactions by iron-containing enzymes.     

Positional cloning of zebrafish ferroportin1 identifies a conserved vertebrate iron exporter

Defects in iron absorption and utilization lead to iron deficiency and overload disorders. Adult mammals absorb iron through the duodenum, whereas embryos obtain iron through placental transport. Iron uptake from the intestinal lumen through the apical surface of polarized duodenal enterocytes is mediated by the divalent metal transporter, DMTi. A second transporter has been postulated to export iron across the basolateral surface to the circulation. Here we have used positional cloning to identify the gene responsible for the hypochromic anaemia of the zebrafish mutant weissherbst. The gene, ferroportin1, encodes a multiple-transmembrane domain protein, expressed in the yolk sac, that is a candidate for the elusive iron exporter. Zebrafish ferroportin1 is required for the transport of iron from maternally derived yolk stores to the circulation and functions as an iron exporter when expressed in Xenopus oocytes. Human Ferroportin1 is found at the basal surface of placental syncytiotrophoblasts, suggesting that it also transports iron from mother to embryo. Mammalian Ferroportin1 is expressed at the basolateral surface of duodenal enterocytes and could export cellular iron into the circulation. We propose that Ferroportin1 function may be perturbed in mammalian disorders of iron deficiency or overload.     

重金属污染土壤的植物修复及其机理研究

近年来,作为一种成本低廉、对环境友好的修复方法,重金属污染土壤的植物修复成为环境修复领域的研究热点.早期的研究侧重于超富集植物的发现与实际应用,近来超富集植物重金属富集机理的研究得到了重视.尽管重金属植物累积的生化机制尚未能被完整阐述,但在土壤重金属生物活性、超富集植物重金属的吸收、转运、储存等方面还是取得了大量进展.综述了近年来国内外相关研究工作成果,探讨了该研究领域存在的主要问题,认为在有机鳌合剂如有机酸与氨基酸等对重金属活性、耐性和离子迁移转运系统中所起作用等方面尚需要深入研究.如果在植物重金属吸收、迁移、解毒机理及其影响因素等重金属富集的关键方面能取得进展,则将大大丰富污染土壤重金属修复的研究与应用领域.     

Characterization of a carbohydrate transporter from symbiotic glomeromycotan fungi

The symbiotic relationships between mycorrhizal fungi and plants have an enormous impact on terrestrial ecosystems. Most common are the arbuscular mycorrhizas, formed by fungi belonging to the phylum Glomeromycota. Arbuscular mycorrhizal fungi facilitate the uptake of soil nutrients by plants and in exchange obtain carbohydrates, thus representing a large sink for atmospheric plant-fixed CO(2). However, how carbohydrates are transported through the symbiotic interface is still unknown. Here we report the characterization of the first known glomeromycotan monosaccharide transporter, GpMST1, by exploiting the unique symbiosis of a glomeromycotan fungus (Geosiphon pyriformis) with cyanobacteria. The GpMST1 gene has a very low GC content and contains six introns with unusual boundaries. GpMST1 possesses twelve predicted transmembrane domains and functions as a proton co-transporter with highest affinity for glucose, then mannose, galactose and fructose. It belongs to an as yet uncharacterized phylogenetic monosaccharide transporter clade. This initial characterization of a new transporter family involved in fungal symbiosis will lead to a better understanding of carbon flows in terrestrial environments.     

铁氨氧化在环境系统中的研究进展及其应用性探究

近年来,厌氧氨氧化耦合Fe(III)还原过程(Feammox)作为一种新型的脱氮技术,在环境系统中被广泛发现和研究。Feammox从热力学角度分析在不同环境中(高地土壤、水稻土、河岸沉积物、湿地沉积物)的代谢产物不同(N₂、NO_2^-、NO_3^-)。环境因素影响着Feammox脱氮效果,本文从铁电极、pH、溶解氧(DO)、温度、Fe(III)浓度等方面探讨Feammox的过程控制。对于Feammox过程中的作用微生物还缺乏统一定论,其中尤以铁还原菌、Acidimicrobiaceae bacterium A6、厌氧氨氧化菌属为主要代表。本文就Feammox反应机理、影响因素、微生物多样性及工程适用性分析角度来归纳总结近年来的研究进展及应用型探究,并对未来发展和应用进行展望。     

A new synthetic approach to the ferritin core uncovers the soluble iron(III) oxo-hydroxo aggregate [Fe11O6(OH)6(O2CPh)15]

Hydrolytic polymerization of iron(III) occurs in many reactions in vivo, for example, the formation of bacterial magnetite in magnetotactic organisms, biomineralization of iron and the synthesis of the metallic core of the iron-storage protein ferritin. The ferritin core contains aggregates of up to 4,500 oxygen-bridged, octahedrally coordinated, high-spin iron(III) centres and is attached to the protein shell through carboxylate groups of amino-acid side chains. The X-ray and electron-diffraction patterns of this core resemble those of the mineral ferrihydrite, a hydrated iron oxide formed in nature, inter alia, by iron-dependent bacteria. The preparation and structural characterization of such large poly-iron aggregates has been a challenge to inorganic chemists. We have recently shown that tri- and tetranuclear iron(III) oxo complexes of the type thought to be important in ferritin-core formation can be prepared by reacting mononuclear [FeCl4]- and binuclear [Fe2OCl6]2- components in aprotic solvents (ref. 9 and S.M.G., W. H. Armstrong and S.J.L., in preparation). Here we report the discovery of a remarkable new molecule, [Fe11O6(OH)6(O2CPh)15], obtained by hydrolysis of the [Fe2O]4+ unit in the presence of limited amounts of water and carboxylate salts. The synthesis and properties of this soluble iron(III) oxohydroxo aggregate should help to elucidate the mechanism of formation of poly-iron centres.     

催化动力学光度法测定痕量铁-Fe(Ⅲ)-KBrO_3-酸性铬蓝K体系

本文研究了在稀硫酸介质中,痕量铁(Ⅲ)催化溴酸钾氧化酸性铬蓝K褪色的新指示反应及动力学条件,建立了催化动力学光度法测定痕量铁的新方法。方法的灵敏度为9.6×1O~(-10)gEe(Ⅲ)/ml。线性范围为0.05—3.5μgFe(Ⅲ)/25ml。方法用于环境水样和人发中痕量铁的测定,结果满意。     

丛枝菌根真菌对氮素的吸收作用和机制

丛枝菌根真菌可以与绝大多数陆生植物共生,它可以吸收铵态氮、硝态氮、一些氨基酸和一些复杂的有机氮素,吸收的氮素在根外菌丝中转化成精氨酸,并以这种形式运输到根内菌丝,在根内菌丝和根细胞界面,精氨酸再进一步转化为NH4^＋后转移到宿主植物体,参与植物氮素代谢,而转移的氮量及对宿主植物氮营养的贡献与宿主植物、真菌以及基质养分和水分条件有关．     

改变镉生物有效性对植物吸收积累镉的影响

土壤镉的生物有效性受土壤成分和土壤环境条件的影响,有机质、pH、氧化还原电位等的变化都会影响土壤中镉由有机结合态和残渣态一不能被植物吸收积累的镉形态向可交换态、碳酸盐态、铁锰氧化态一容易被植物吸收利用的形态转化．一些土壤改良剂、有机物料、营养元素以及微生物都可以改变土壤镉的有效性,进一步影响植物积累镉的量,对植物生长及品质造成影响．由于有效态镉直接影响植物对镉的吸收积累,寻找有利途径以减少土壤有效态从而降低植物对镉的吸收显得非常关键．     

Mitoferrin is essential for erythroid iron assimilation

Iron has a fundamental role in many metabolic processes, including electron transport, deoxyribonucleotide synthesis, oxygen transport and many essential redox reactions involving haemoproteins and Fe-S cluster proteins. Defective iron homeostasis results in either iron deficiency or iron overload. Precise regulation of iron transport in mitochondria is essential for haem biosynthesis, haemoglobin production and Fe-S cluster protein assembly during red cell development. Here we describe a zebrafish mutant, frascati (frs), that shows profound hypochromic anaemia and erythroid maturation arrest owing to defects in mitochondrial iron uptake. Through positional cloning, we show that the gene mutated in the frs mutant is a member of the vertebrate mitochondrial solute carrier family (SLC25) that we call mitoferrin (mfrn). mfrn is highly expressed in fetal and adult haematopoietic tissues of zebrafish and mouse. Erythroblasts generated from murine embryonic stem cells null for Mfrn (also known as Slc25a37) show maturation arrest with severely impaired incorporation of 55Fe into haem. Disruption of the yeast mfrn orthologues, MRS3 and MRS4, causes defects in iron metabolism and mitochondrial Fe-S cluster biogenesis. Murine Mfrn rescues the defects in frs zebrafish, and zebrafish mfrn complements the yeast mutant, indicating that the function of the gene may be highly conserved. Our data show that mfrn functions as the principal mitochondrial iron importer essential for haem biosynthesis in vertebrate erythroblasts.     

大型厌氧填埋场中铁的分布特征及迁移行为研究

以北京南郊某大型厌氧填埋场为例, 对不同填埋龄垃圾中的铁含量、价态转换及形态分布进行研究。结果表明, 该厌氧填埋场填埋龄为3~10年的垃圾中Fe含量变化范围为18532.8~26897.2 mg/kg。由于微生物的异化铁还原作用, Fe(III)不断被还原为Fe(II), Fe(II)/ Fe(III)从0.51上升到1.01。形态分析结果表明: Fe在不同填埋龄垃圾中的形态分布规律基本一致, 残渣态含量最高, 可氧化态和可还原态次之, 酸可溶解态含量最低, 可还原态受环境因素影响极大, 硫化物对Fe形态分布影响最显著。     

铁限制诱导对聚球藻转录组的影响

为探究Fe元素限制对聚球藻转录组的影响,该文以聚球藻Synechococcus sp. PCC 7002为研究对象,采用高通量测序技术对经过铁限制处理的聚球藻Synechococcus sp. PCC 7002进行转录组分析.以铁的3种摩尔浓度进行处理,其中每组数据重复3次实验,一共获得9组实验数据; 对照组摩尔浓度为10.900 nmol·L^-1,铁限制组摩尔浓度分别为0.410、0.003 nmol·L^-1.实验发现:在铁限制环境下,聚球藻通过增加对胞外铁摄取、上调光合作用相关蛋白的表达和调整代谢通路来应对缺铁环境,且铁限制程度与差异基因数量成正相关关系.此外,在强缺铁时通过下调CRISPR系统中某些核酸酶的表达来影响聚球藻抵御外源病毒感染的能力,其转运磷酸基团ABC转运蛋白表达水平下降,从而极大地影响了聚球藻的生存.     

印染废水CWAO法处理中均相催化剂的研制

为了制备用于催化湿式氧化法处理高浓度印染废水的催化剂,实验中以COD达2 000 mg.L-1的亚甲蓝水溶液作降解对象,用均相催化湿式氧化法进行处理,催化剂性能以COD去除率和脱色率进行评价.在对19种可溶盐进行普选的基础上,对双组分催化剂进行复配.结果表明:铜盐和铁盐的催化活性居于前列,而硫酸铜和硫酸亚铁复配的Cu1Fe1催化剂在活性和成本上显示了优越性,同等条件下对水样的COD去除率比不加催化剂时提高约50%.对Cu1Fe1的作用机理分析表明,自由基反应以及Fe(Ⅲ)聚合物的混凝同时发挥了作用.     

拟南芥SnRK2.2/2.3激酶参与调节镉胁迫响应的机制探究

为探究拟南芥SnRK2.2和SnRK2.3基因对Cd胁迫响应的分子机制. 以野生型（WT）、双突变体SnRK2.2/2.3、过表达SnRK2.2和过表达SnRK2.3的转基因植物为材料,研究SnRK2.2和SnRK2.3基因与Cd胁迫响应的关系.发现过表达两个基因可以提高拟南芥对Cd的耐受性,表现为可以减少Cd、丙二醛（MDA）及活性氧（ROS）的累积量,增加抗氧化酶CAT、POD和SOD的活性. qRT PCR结果显示在Cd胁迫下,两种过表达植株中铁转运蛋白IRT1和转录因子FIT、bHLH038和bHLH039表达水平受到明显抑制,ABA合成相关基因AAO3和NCED3的表达量显著上调.在Cd胁迫下,两种过表达植株中ABA含量显著高于WT和双突变体. 以上结果表明：拟南芥遭受Cd胁迫时,SnRK2.2和SnRK2.3基因通过下调IRT1基因表达从而减少植物对Cd的吸收,同时通过增加内源ABA含量来缓解Cd对植物的毒害.     

A silicon transporter in rice

Silicon is beneficial to plant growth and helps plants to overcome abiotic and biotic stresses by preventing lodging (falling over) and increasing resistance to pests and diseases, as well as other stresses. Silicon is essential for high and sustainable production of rice, but the molecular mechanism responsible for the uptake of silicon is unknown. Here we describe the Low silicon rice 1 (Lsi1) gene, which controls silicon accumulation in rice, a typical silicon-accumulating plant. This gene belongs to the aquaporin family and is constitutively expressed in the roots. Lsi1 is localized on the plasma membrane of the distal side of both exodermis and endodermis cells, where casparian strips are located. Suppression of Lsi1 expression resulted in reduced silicon uptake. Furthermore, expression of Lsi1 in Xenopus oocytes showed transport activity for silicon only. The identification of a silicon transporter provides both an insight into the silicon uptake system in plants, and a new strategy for producing crops with high resistance to multiple stresses by genetic modification of the root's silicon uptake capacity.