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1.
To show the effects of growth inhibitory factor (Cu4Zn3MT-III) involved in the scavenging of reactive oxygen species (ROS), a pulse radiolytic study was employed using N2O-saturated Cu4Zn3MT-III aqueous solutions. It was demonstrated that the oxidizing OH radical efficiently reacted with Cu4Zn3MT-III by forming a thiyl radical RS with a second-order constant of 1.46×1011 mol l–1s–1, which was determined by competition kinetics against KSCN. The thiyl radical RS reacted rapidly and reversibly with a thiolate in Cu4Zn3MT-III to form radical anion RSSR with a constant of 1.65×109 mol lL–1s–1 per thiolate, while the constant of the decay of this radical anion was 2.72×105 s–1, and the equilibrium constant of the formation for RSSR was 6.08×103 mol–1 l. These values were close to those of Cd5Zn2MT-II. The SOD activity of Cu4Zn3MT-III to quench O2 was assayed by the riboflavine-methionine-nitrobluetetrazolium (NBT) method which catalyzed the dismutation of superoxide (O2 ) at pH 7.8 with an IC50 value of 1.50×10–6 M for Cu4Zn3MT-III and 1.62×10–6 M for Cd5Zn2MT-II. Additionally, the down-regulation of GIF may be a main factor in the decrease of the scavenging ability for the free OH and O2 radicals, which is possibly associated with the pathogenesis of neurodegenerative disease.  相似文献   

2.
Neuronal growth inhibitory factor (GIF) is a small cysteine-rich metal binding protein downregulated in Alzheimer's disease. The protein belongs to the superfamily of metallothioneins (MTs) and was classified as MT-3. Although first identified as a brain specific protein, several reports now indicate a substantially broader expression pattern. However, currently available detection methods for MT-3 show low sensitivity in gel electrophoresis and Western blot. We have developed a fast and sensitive method for MT-3 detection in SDS-PAGE (detection limit approximately 10 ng) and Western blot (detection limit approximately 1 ng). The method is based on the chemical modification of cysteine residues with the dye monobromobimane and an improved blotting protocol.  相似文献   

3.
Metallothioneins (MTs) are ubiquitous cysteine-rich proteins with a high affinity for divalent metal ions such as ZnII, CuI, and CdII that are involved in metal ion homeostasis and detoxification, as well as protection against reactive oxygen species. Here we show the NMR solution structure of the βE-domain of the early cysteine-labeled protein (Ec-1) from wheat (βE-Ec-1), which represents the first three-dimensional structure of a plant MT. The βE-domain comprises the 51 C-terminal residues of Ec-1 and exhibits a distinctive unprecedented structure with two separate metal-binding centers, a mononuclear ZnII binding site constituted by two cysteine and two highly conserved histidine residues as found in certain zinc-finger motifs, and a cluster formed by three ZnII ions coordinated by nine Cys residues that resembles the cluster in the β-domain of vertebrate MTs. Cys-metal ion connectivities were determined by exhaustive structure calculations for all 7560 possible configurations of the three-metal cluster. Backbone dynamics investigated by 15N relaxation experiments support the results of the structure determination in that βE-Ec-1 is a rigidly folded polypeptide. To further investigate the influence of metal ion binding on the stability of the structure, we replaced ZnII with CdII ions and examined the effects of metal ion release on incubation with a metal ion chelator.  相似文献   

4.
The metal binding preference of metallothioneins (MTs) groups them in two extreme subsets, the Zn/Cd- and the Cu-thioneins. Ciliates harbor the largest MT gene/protein family reported so far, including 5 paralogs that exhibit relatively low sequence similarity, excepting MTT2 and MTT4. In Tetrahymena thermophila, three MTs (MTT1, MTT3 and MTT5) were considered Cd-thioneins and two (MTT2 and MTT4) Cu-thioneins, according to gene expression inducibility and phylogenetic analysis. In this study, the metal-binding abilities of the five MTT proteins were characterized, to obtain information about the folding and stability of their cognate- and non-cognate metal complexes, and to characterize the T. thermophila MT system at protein level. Hence, the five MTTs were recombinantly synthesized as Zn2+-, Cd2+- or Cu+-complexes, which were analyzed by electrospray mass spectrometry (ESI-MS), circular dichroism (CD), and UV-vis spectrophotometry. Among the Cd-thioneins, MTT1 and MTT5 were optimal for Cd2+ coordination, yielding unique Cd17- and Cd8- complexes, respectively. When binding Zn2+, they rendered a mixture of Zn-species. Only MTT5 was capable to coordinate Cu+, although yielding heteronuclear Zn-, Cu-species or highly unstable Cu-homometallic species. MTT3 exhibited poor binding abilities both for Cd2+ and for Cu+, and although not optimally, it yielded the best result when coordinating Zn2+. The two Cu-thioneins, MTT2 and MTT4 isoforms formed homometallic Cu-complexes (major Cu20-MTT) upon synthesis in Cu-supplemented hosts. Contrarily, they were unable to fold into stable Cd-complexes, while Zn-MTT species were only recovered for MTT4 (major Zn10-MTT4). Thus, the metal binding preferences of the five T. thermophila MTs correlate well with their previous classification as Cd- and Cu-thioneins, and globally, they can be classified from Zn/Cd- to Cu-thioneins according to the gradation: MTT1>MTT5>MTT3>MTT4>MTT2. The main mechanisms underlying the evolution and specialization of the MTT metal binding preferences may have been internal tandem duplications, presence of doublet and triplet Cys patterns in Zn/Cd-thioneins, and optimization of site specific amino acid determinants (Lys for Zn/Cd- and Asn for Cu-coordination).  相似文献   

5.
In rat striatal slices labelled with [3H]-adenine and in the presence of 1 mM 3-isobutyl-1-methylxantine (IBMX), cyclic [3H]-AMP ([3H]-cAMP) accumulation induced by the dopamine D1 receptor agonist SKF-81297 (1 μM; 177±13% of basal) was inhibited by the general muscarinic agonist carbachol (maximum inhibition 72±3%, IC50 0.30±0.06 μM). The muscarinic toxin 7 (MT-7), a selective antagonist at muscarinic M1 receptors, reduced the effect of SKF-81297 by 40±7% (IC50 251±57 pM) and enhanced the inhibitory action of a submaximal (1 μM) concentration of carbachol (69±4% vs. 40±7% inhibition, IC50 386±105 pM). The toxin MT-1, agonist at M1 receptors, stimulated [3H]-cAMP accumulation in a modest but significant manner (137±11% of basal at 400 nM), an action additive to that of D1 receptor activation and blocked by MT-7 (10 nM). The effects of MT-7 on D1 receptor-induced [3H]-cAMP accumulation and the carbachol inhibition were mimicked by the PKC inhibitors Ro-318220 (200 nM) and Gö-6976 (200 nM). Taken together our results indicate that in addition to the inhibitory role of M4 receptors, in rat striatum acetylcholine stimulates cAMP formation through the activation of M1 receptors and PKC stimulation.  相似文献   

6.
Metallothioneins (MTs) are cysteine-rich metal-binding proteins that are involved in cell growth regulation, transportation of metal ions and detoxification of heavy metals. A mesocarp-specific metallothionein-like gene (MT3-A) promoter was isolated from the oil palm (Elaeis guineensis Jacq). A vector construct containing the MT3-A promoter fused to the β-glucuronidase (GUS) gene in the pCAMBIA 1304 vector was produced and used in Agrobacterium-mediated transformation of tomato. Histochemical GUS assay of different tissues of transgenic tomato showed that the MT3-A promoter only drove GUS expression in the reproductive tissues and organs, including the anther, fruit and seed coat. Competitive RT-PCR and GUS fluorometric assay showed changes in the level of GUS mRNA and enzyme activity in the transgenic tomato (T0). No GUS mRNA was found in roots and leaves of transgenic tomato. In contrast, the leaves of transgenic tomato seedlings (T1) produced the highest GUS activity when treated with 150 μM Cu2+ compared to the control (without Cu2+). However, Zn2+ and Fe2+ treatments did not show GUS expression in the leaves of the transgenic tomato seedlings. Interestingly, the results showed a breaking-off tissue-specific activity of the oil palm MT3-A promoter in T1 seedlings of tomato when subjected to Cu2+ ions.  相似文献   

7.
Zn2+ caused a noninhibitory binding of IF1 to mitochondrial membranes in both rabbit heart SMP and intact rabbit heart mitochondria. This Zn2+-induced IF1 binding required the presence of at least trace amounts of MgATP and was essentially independent of pH between 6.2 and 8.2. Addition of Zn2+ after the formation of fully inhibited IF1-ATPase complexes very slowly reversed IF1-mediated ATPase inhibition without causing significant IF1 release from the membranes. When Zn2+ was added during the state 4 energization of ischemic mitochondria in which IF1 was already functionally bound, it slowed somewhat energy-driven ATPase activation. This slowing was probably due to the fairly large depressing effect Zn2+ had upon membrane potential development, but Zn2+ did not decrease the degree of ATPase activation eventually reached at 20 min of state 4 incubation. Zn2+ also preempted normal IF1 release from the membranes, causing what little inhibitor that was released to rebind to the enzyme in noninhibitory IF1-ATPase complexes. The data suggest that IF1 can interact with the ATPase in two ways or through two kinds of sites: (a) a noninhibitory interaction involving a noninhibitory IF1 conformation and/or and IF1 docking site on the enzyme and (b) an inhibitory interaction involving an inhibitory IF1 conformation and/or a distinct ATPase activity regulatory site. Zn2+ appears to have the dual effect of stabilizing the noninhibitory IF1-ATPase interaction and possibily a noninhibitory IF1 conformation while concomitantly preventing the formation of an inhibitory IF1-ATPase interaction and possibly an inhibitory IF1 conformation, regardless of pH. While the data do not rule out direct effects of Zn2+ on either free IF1 or the free enzyme, they suggest that Zn2+ cannot interact readily with either the inhibitor or the enzyme once functional IF1-ATPase complexes are formed.  相似文献   

8.
生长抑制因子(GIF)与G蛋白Rab3a直接相互作用   总被引:6,自引:1,他引:5  
生长抑制因子(growth inhibitory factor, GIF), 又称金属硫蛋白-3, 为68个氨基酸组成的脑特异性金属硫蛋白, 具有广泛的生理功能; GIF可能与阿尔茨海默氏症(Alzheimer's)病理相关, 在Alzheimer's脑提取物存在下, 还对神经细胞具有特异的生长抑制活性.然而, 对其发挥生长抑制作用的分子机制并不清楚.运用酵母双杂交系统从人脑cDNA文库中筛选与GIF相互作用因子,从4.1×106个人脑cDNA文库转化子中,首次筛选到Ras家族G蛋白Rab3a C端,包含87个氨基酸的片段能与GIF相互作用;用PCR自人胎盘总cDNA中获得包含完整Rab3a编码序列的cDNA;通过酵母双杂交实验表明,全长Rab3a蛋白亦能与GIF相互作用.免疫共沉淀和蛋白质印迹实验进一步验证了GIF与Rab3a在哺乳动物细胞中可以相互作用; 而且, Rab3a是以GTP结合形式(GTP-Rab3a)与GIF发生相互作用.  相似文献   

9.
以2年生金银花为试验材料,采用叶面喷施法,研究不同浓度的苯丙氨酸(Phe)、酪氨酸(Lyr)以及锌(Zn2+)、铜(Cu2+)对金银花生长发育和质量的影响。结果显示:(1)喷施不同浓度的Phe、Lyr以及Zn2+、Cu2+对叶面积无明显影响;不同处理的叶绿素含量随喷施次数的增加而出现不同程度的下降,喷施浓度适宜则有助于叶绿素的合成;喷施一定浓度的Phe、Lyr以及Zn2+、Cu2+可增加花蕾重量,如经1 000mg/g Phe处理后的花蕾鲜重与干重较对照增加了20.1%和51.4%。(2)不同浓度的Phe、Lyr可显著影响碳代谢,但对氮代谢影响不明显;Zn2+、Cu2+对碳氮代谢产物影响较明显,如喷施10mg/L的CuSO4及ZnSO4可提高可溶性糖及淀粉含量。(3)除Zn2+处理后的花蕾类黄酮含量显著低于对照外,其他处理较CK无显著差异;花蕾总黄酮含量均显著低于对照,但绿原酸含量均高于对照。(4)叶片中离子含量受喷施次数及浓度影响较明显,除30mg/L CuSO4处理外,其它处理的花蕾中Zn2+、Cu2+、Fe2+含量均显著低于对照。研究表明,在金银花的第一茬花抽枝初期喷施适宜浓度的Phe、Lyr(如1 000mg/g Phe、2 000mg/g Lyr)以及Zn2+、Cu2+(如50mg/L ZnSO4、10mg/L CuSO4)可改善金银花的生长发育,并提高产量和质量。  相似文献   

10.
Two new zinc(II)-triazole-aliphatic dicarboxylate coordination polymers, [Zn(trz)(Hsuc)]n (1), [Zn2(trz)2(tar)]n (2), have been hydrothermally synthesized by reaction of Zn salt, Htrz with H2suc and H2tar, respectively (Htrz = 1,2,4-triazole, H2suc = succinic acid, H2tar = tartaric acid).Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by X-ray powder diffraction, elemental analyses, IR spectra and TG analyses. Compound 1 displays a 2D layer structure containing {[Zn4(trz)4]4+}n layers decorated by the suc ligand. Compound 2 is in a 3D structure formed by the interconnection of 2D {[Zn4(trz)4]4+}n layers with tar ligand, resulting a 3,4-connected topological network. Due to the different coordination mode and conformation of aliphatic carboxylate ligand, the similar 2D {[Zn4(trz)4]4+}n layers stack in the -AAA- fashion in 1, while the {[Zn4(trz)4]4+}n layers hold together in the -ABAB- stacking sequence in 2. Additionally, the two compounds show strong fluorescence in the solid state at room temperature.  相似文献   

11.
In addition to the well known catalytically accelerated O2 dismutation, Cu2Zn2 Superoxide dismutase (SOD) reversibly reduces NO to NO with the consequence of a prolonged half-life of NO. This alternative reactivity was examined in the presence of the intact CuZn enzyme and a diSchiff base copper complex prepared from putrescine and pyridine-2-aldehyde (Cu-PuPy) which is known as a convenient active center analog of the former copper protein. The reaction of this SOD mimick with NO and NO was monitored by electronic absorption and electron paramagnetic resonance (EPR) spectroscopy via the formation of nitrosylmyoglobin. Cu-PuPy reacted up to three times faster with NO compared with Cu2Zn2 SOD and 15 times faster in comparison with CuSO4 and copper EDTA. The oxidation rate of NO by Cu-PuPy was up to 300% higher compared with the reactivities of CuSO4 and Cu EDTA. Cu2Zn2SOD reacted with NO to a neglible extent only. Catalytic characteristics could be observed in the course of the oxidation of NO in concentrations between 1 and 20 M copper. Disturbances of the EPR properties suggested a modification of the chemical environment at the copper sites in both the copper complex and the enzyme. As a consequence, no further reactions of the nitrogen monoxides with the respective active centers were seen. In conclusion, Cu-PuPy appears to be an efficient moderator of the biochemical reactivity of nitrogen monoxides attributable to the observed increased half-life of NO.  相似文献   

12.
Human metallothioneins, small cysteine- and metal-rich proteins, play an important role in the acquired resistance to platinum-based anticancer drugs. These proteins contain a M(II)4(CysS)11 cluster and a M(II)3(CysS)9 cluster localized in the α-domain and the β-domain, respectively. The noninducible isoform metallothionein-3 (Zn7MT-3) is mainly expressed in the brain, but was found overexpressed in a number of cancer tissues. Since the structural properties of this isoform substantially differ from those of the ubiquitously occurring Zn7MT-1/Zn7MT-2 isoforms, the reactions of cis-diamminedichloridoplatinum(II) (cisplatin) and trans-diamminedichloridoplatinum(II) (transplatin) with human Zn7MT-3 were investigated and the products characterized. A comparison of the reaction kinetics revealed that transplatin reacts with cysteine ligands of Zn7MT-3 faster than cisplatin. In both binding processes, stoichiometric amounts of Zn(II) were released from the protein. Marked differences between the reaction rates of cisplatin and transplatin binding to Zn7MT-3 and the formation of the Pt–S bonds suggest that the binding of both Pt(II) compounds is a complex process, involving at least two subsequent binding steps. The electrospray ionization mass spectrometry characterization of the products showed that whereas all ligands in cisplatin were replaced by cysteine thiolates, transplatin retained its carrier ammine ligands. The 113Cd NMR studies of Pt1 113Cd6MT-3 revealed that cisplatin binds preferentially to the β-domain of the protein. The rates of reaction of cisplatin and transplatin with Zn7MT-3 were much faster than those of cisplatin and transplatin with Zn7MT-2. The biological consequences of a substantially higher reactivity of cisplatin toward Zn7MT-3 than Zn7MT-2 in the acquired resistance to platinum-based drugs are discussed.  相似文献   

13.

Background

A major pathological hallmark of AD is the deposition of insoluble extracellular β-amyloid (Aβ) plaques. There are compelling data suggesting that Aβ aggregation is catalysed by reaction with the metals zinc and copper.

Methodology/Principal Findings

We now report that the major human-expressed metallothionein (MT) subtype, MT-2A, is capable of preventing the in vitro copper-mediated aggregation of Aβ1–40 and Aβ1–42. This action of MT-2A appears to involve a metal-swap between Zn7MT-2A and Cu(II)-Aβ, since neither Cu10MT-2A or carboxymethylated MT-2A blocked Cu(II)-Aβ aggregation. Furthermore, Zn7MT-2A blocked Cu(II)-Aβ induced changes in ionic homeostasis and subsequent neurotoxicity of cultured cortical neurons.

Conclusions/Significance

These results indicate that MTs of the type represented by MT-2A are capable of protecting against Aβ aggregation and toxicity. Given the recent interest in metal-chelation therapies for AD that remove metal from Aβ leaving a metal-free Aβ that can readily bind metals again, we believe that MT-2A might represent a different therapeutic approach as the metal exchange between MT and Aβ leaves the Aβ in a Zn-bound, relatively inert form.  相似文献   

14.
Heavy metals are common pollutants of the coastal saline area and Salicornia brachiata an extreme halophyte is frequently exposed to various abiotic stresses including heavy metals. The SbMT-2 gene was cloned and transformed to tobacco for the functional validation. Transgenic tobacco lines (L2, L4, L6 and L13) showed significantly enhanced salt (NaCl), osmotic (PEG) and metals (Zn++, Cu++ and Cd++) tolerance compared to WT plants. Transgenic lines did not show any morphological variation and had enhanced growth parameters viz. shoot length, root length, fresh weight and dry weight. High seed germination percentage, chlorophyll content, relative water content, electrolytic leakage and membrane stability index confirmed that transgenic lines performed better under salt (NaCl), osmotic (PEG) and metals (Zn++, Cu++ and Cd++) stress conditions compared to WT plants. Proline, H2O2 and lipid peroxidation (MDA) analyses suggested the role of SbMT-2 in cellular homeostasis and H2O2 detoxification. Furthermore in vivo localization of H2O2 and O2 ; and elevated expression of key antioxidant enzyme encoding genes, SOD, POD and APX evident the possible role of SbMT-2 in ROS scavenging/detoxification mechanism. Transgenic lines showed accumulation of Cu++ and Cd++ in root while Zn++ in stem under stress condition. Under control (unstressed) condition, Zn++ was accumulated more in root but accumulation of Zn++ in stem under stress condition suggested that SbMT-2 may involve in the selective translocation of Zn++ from root to stem. This observation was further supported by the up-regulation of zinc transporter encoding genes NtZIP1 and NtHMA-A under metal ion stress condition. The study suggested that SbMT-2 modulates ROS scavenging and is a potential candidate to be used for phytoremediation and imparting stress tolerance.  相似文献   

15.
Metallothioneins (MTs) are ubiquitous low molecular mass, cysteine-rich proteins with the ability to bind d10 metal ions in the form of metal-thiolate clusters. In contrast to the vertebrate forms, knowledge about the properties of members of the plant metallothionein family is still scarce. The amino acid sequences of plant MTs are distinctively different to the sequences of other MT species. The protein under investigation, Musa acuminata (banana) MT3, belongs to the plant MT fruit-specific p3 subfamily. With a total of 10 cysteine residues, MT3 features a cysteine content and percentage that is more comparable to fungal and prokaryotic MTs than to the well characterized mammalian iso-forms. The gene sequence encoding MT3 was cloned into a suitable vector and the protein was recombinantly overexpressed in Escherichia coli. MT3 is able to coordinate a maximum of four divalent d10 metal ions under the formation of metal-thiolate clusters. The hitherto unknown spectroscopic behavior of MT3 in combination with the metal ions Zn2+, Cd2+, Pb2+, and Hg2+ will be presented and gives rise to the existence of a weaker metal ion coordination site. The pH stability of the investigated zinc and cadmium clusters is comparable to the values found for other plant metallothioneins though significantly lower than for the mammalian iso-forms. Possible metal-thiolate cluster structures will additionally be discussed.  相似文献   

16.
金属硫蛋白 3(MT 3) ,又称神经生长抑制因子 ,主要表达于中枢神经系统。它属于金属硫蛋白家族 ,但具有几项其他家族蛋白质如MT 1/ 2等所不具有的独特性质 ,是一种多功能蛋白质 ,可在中枢神经系统中发挥重要的神经调节和神经保护作用 ,但是具体发挥机制还很不清楚。实验以人神经母细胞瘤细胞系SH SY5Y为模型 ,运用最近发展起来的比较蛋白质组学研究方法对MT 3基因瞬时转染引起的SH SY5Y细胞蛋白质的整体变化进行了系统的研究。经考马斯亮蓝染色 ,结果表明 ,MT 3转基因后平均每块胶上可检测到约 75 0个蛋白质点。利用ImageMaster 2DElite软件对胶上的蛋白质点进行半定量分析 ,发现共有 17个蛋白质点呈显著的变化 :和对照组比较 ,在这 17个点中 ,有 12个表达明显上调 ,有 5个表达水平明显下降 ,实验结果具有可重复性。结合pI值和分子量 ,应用基质辅助激光解吸 /电离飞行时间质谱对这 17个点进行分析 ,鉴定了其中 10个点 ,包括类锌指蛋白 ,谷氨酸转运蛋白和增强蛋白等。这些蛋白质都可在神经系统功能的调节中发挥作用。实验结果表明MT 3可能是通过调节和 /或协同这些蛋白质来发挥它的多种功能的。  相似文献   

17.
A sterile hydroponic culture system suitable for studying nitrogen (N) uptake ofLagerstroemia indica L.in vitro was developed. Four different treatments were assayed: with and without activated charcoal (AC and NAC, respectively), with and without 50 μM of 6-benzyladenine (+BA and −BA, respectively). Medium pH, electrical conductivity (EC), NO3 and NH4 + concentrations were measured weekly. At the end of the culture, propagules were sampled and SPAD indices, and shoot and root fresh weights were determined. Explants grown in media with activated charcoal were able to take up both NO3 and NH4 +, although NH4 + uptake was lower. Subsequently the pH of the media was maintained between 5.5–6.0. In treatments with no addition of activated charcoal, NH4 + uptake was preferential and the pH dropped to 3.1. Explants in these conditions were unable to raise the pH by taking up NO3 , especially when root morphogenesis was inhibited by addition of BA. Supply of this PGR produced root growth inhibition, which was almost complete in the treatment without activated charcoal. This component significantly reduced the inhibitory effect of 50 μM BA on root growth. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

18.
Summary The purpose of this study was to investigate the phytotoxicity of nitrapyrin 2-chloro-6-(trichloromethyl)pyridine to sunflower (Helianthus annuus L.) under different N regimes and to see if N forms affect the phytotoxicity of nitrapyrin. Sunflower was grown in pot culture for 21 days and was fertilized with (NH4)2SO4, NH4NO3 and NaNO3 to provide 0, 100 and 200 ppm N and with nitrapyrin application of 0 and 20 ppm. All N-treated sunflower plants in all N regimes and regardless of titrapyrin treatment produced more root and shoot dry weights and contained a significantly higher N than untreated check. Nitrapyrin toxicity appeared as a curling of leaf margin and a tendril type of stem growth, the visible toxicity symptoms decreased in the order: (NH4)2SO4>NH4NO3>NaNO3. Furthermore nitrapyrin addition suppressed sunflower growth in each N regime, the suppressing effect being greater with (NH4)2SO4 and NH4NO3 than as with NaNO3. Although, shoot growth from plants receiving nitrapyrin was not significantly affected by any N regime, root growth of nitrapyrin-treated plants was somewhat restricted by NH4 +−N nutrition relative to NO3 −N nutrition.  相似文献   

19.
The primary objectives of this study were to determine (1) the exchange characteristics of various soil amendments using a range of salt solutions, (2) the effect of selected soil amendments on heavy metal (Cu2+, Pb2+, and Zn2+) availability, and (3) the effect of selected soil amendments on NH4 + and P availability. The CEC of zeolite and red mud obtained using solutions of 0.1?M BaCl2 and 0.1?M BaCl2/NH4Cl were significantly lower than values obtained using 1?M KCl and 1?M NH4Cl. The higher CEC obtained with monovalent cations indicated that larger divalent cations could not enter the mineralogical framework of zeolite and red mud, and, consequently, a number of exchange sites were only accessible to the smaller monovalent cations. These findings suggest that 1?M KCl and 1?M NH4NO3 should be used as the extracting solutions to obtain the best estimation of CEC and ECEC of red mud and zeolite. The ability of red mud, zeolite, and calcium phosphate (Ca-P), mixed at rates of 0%, 5%, 10%, and 20% (w/w), to sorb Cu2+, Pb2+, and Zn2+ generally followed the order: red mud>zeolite>>Ca-P, while the affinity sequence for these metals followed the order: Pb2+≥Cu2+>>Zn2+. The higher affinity of the sand/amendment mixtures for Pb2+ and Cu2+ relative to Zn2+ was attributed to metal hydrolysis and subsequent specific adsorption as Pb(OH)+ and Cu(OH)+. Zinc was considered to have been primarily sorbed as the divalent cation species. Rates of 5% (w/w) adequately reduced the availability of heavy metals to concentrations below environmental guidelines based on the Toxicity Characteristic Leaching Procedure. Red mud and zeolite added at a rate of 10% (w/w) to the A and B horizon of a sandy soil significantly increased their ability to remove NH4 + from solution, but had negligible effect on P sorption compared with unamended soils. Increased NH4 + removal was attributed to the associated increase in CEC and the greater selectivity of the exchange sites for this cation relative to resident exchangeable Ca2+ and Na+. The absence of P sorption by these two amendments was attributed to the high pH and predominantly negative surface charge of the red mud and the lack of sorption sites in zeolite. Gypsum, on the other hand, tended to depress NH4 + retention but markedly increased P sorption. The depressive effect on NH4 + was due to increased competition between NH4 + and Ca2 + for a limited number of exchange sites, while formation of calcium phosphates of low solubility was the possible mechanism for increased P sorption.  相似文献   

20.
We investigated the effects on ginseng adventitious root growth and ginsenoside production when macro-element concentrations and nitrogen source were manipulated in the culture media. Biomass growth was greatest in the medium supplemented with 0.5-strength NH4PO3, whereas ginsenoside accumulation was highest (9.90 mg g-1 DW) in the absence of NH4PO3. At levels of 1.0-strength KNO3, root growth was maximum, but a 2.0 strength of KNO3 led to the greatest ginsenoside content (9.85 mg g-l). High concentrations of MgSO4 were most favorable for both root growth and ginsenoside accumulation (up to 8.89 mg g-1 DW). Root growth and ginsenoside content also increased in proportion to the concentration of CaCI2 in the medium, with the greatest accumulation of ginsenoside (8.91 mg g-1 DW) occurring at a 2.0 strength. The NH4/NO3 -- ratio also influenced adventitious root growth and ginsenoside production; both parameters were greater when the NO3 - concentration was higher than that of NH4 +. Maximum root growth was achieved at an NH4 +/NO3 - ratio of 7.19/18.50, while ginsenoside production was greatest (83.37 mg L-1) when NO3 - was used as the sole N source.  相似文献   

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