Enhancement of emulsifier production by <Emphasis Type="Italic">Curvularia lunata</Emphasis> in cadmium,zinc and lead presence

The influence of cadmium, zinc and lead on fungal emulsifier synthesis and on the growth of filamentous fungus Curvularia lunata has been studied. Tolerance to heavy metals established for C. lunata was additionally compared with the sensitivity exhibited by strains of Curvularia tuberculata and Paecilomyces marquandii—fungi which do not secrete compounds of emulsifying activity. Although C. lunata, as the only one out of all studied fungi, exhibited the lowest tolerance to heavy metals when grown on a solid medium (in conditions preventing emulsifier synthesis), it manifested the highest tolerance in liquid culture - in conditions allowing exopolymer production. Cadmium, zinc and lead presented in liquid medium up to a concentration of 15 mM had no negative effect on C. lunata growth and stimulated emulsifier synthesis. In the presence of 15 mM of heavy metals, both the emulsifier and 24-h-old growing mycelium exhibited maximum sorption capacities, which were determined as 18.2 ± 2.67, 156.1 ± 10.32 mg g⁻¹ for Cd²⁺, 22.2 ± 3.40, 95.2 ± 14.21 mg g⁻¹ for Zn²⁺ and 51.1 ± 1.85, 230.0 ± 28.47 mg g⁻¹ for Pb²⁺ respectively. The results obtained by us in this work indicate that the emulsifier acts as a protective compound increasing the ability of C. lunata to survive in heavy metal polluted environment. Enhancement of exopolymer synthesis in the presence of Cd²⁺, Zn²⁺ and Pb²⁺ may also suggest, at least to some extent, a metal-specific nature of emulsifier production in C. lunata. Due to accumulation capability and tolerance to heavy metals, C. lunata mycelium surrounded by the emulsifier could be applied for toxic metal removal.     

Comparison of Physiological Changes in Euglena gracilis During Exposure to Heavy Metals of Heterotrophic and Autotrophic Cells

The effect of different concentrations of Hg²⁺, Cd²⁺, and Pb²⁺ on ultrastructure, growth, respiration, photosynthesis, chlorophyll content, and metal accumulation in Euglena gracilis was examined. The toxicity of the heavy metals was dependent on the culture medium used and whether cells were grown in the dark or under illumination. Hg²⁺ was the most toxic metal, which showed effects at a concentration as low as 1.5 μM; Cd²⁺ showed an intermediate toxicity (effects observed above 50 μM); and Pb²⁺ was almost ineffective up to 1 mM. Cells grown for several weeks in the dark, in the presence of 1.5 μM Hg²⁺ showed a reduced sensitivity to subsequent exposure to Cd²⁺ or Pb²⁺. The Hg²⁺-pretreated cells also presented an enhanced capacity to accumulate other metals. In comparison, light-grown cells showed a greater Cd²⁺ accumulation, but a lower Pb²⁺ uptake than Hg²⁺-pretreated dark-grown cells. Pretreatment of light-grown cells with Hg²⁺ did not enhance the accumulation of Cd²⁺. These results suggest that the capacity to tolerate heavy metals by Euglena may have mechanistic differences when cells are grown in the dark or under illumination.     

Cd2+和Pb2+对花翅摇蚊(Chironomus kiiensis)幼虫生长发育的影响及富集效应

河流、湖泊等水生环境中普遍存在的重金属污染破坏水生生态系统并间接威胁人类健康。为探究重金属胁迫下水生昆虫花翅摇蚊（Chironomus kiiensis）生态毒理,测定了重金属Cd²⁺和Pb²⁺胁迫对花翅摇蚊化蛹率和羽化率的影响,检测了摇蚊的口器致畸与富集效应。研究结果表明,Cd²⁺和Pb²⁺影响摇蚊幼虫化蛹和羽化过程,单一重金属离子处理14 d Pb²⁺处理组的化蛹率和羽化率分别为22.22%和8.89%,低于Cd²⁺的化蛹率（25.56%）和羽化率（11.11%）,表现出更强的抑制效应。混合离子1：2和2：1配比处理组化蛹率和羽化率均为11.11%和4.44%,显著低于单一重金属离子胁迫下的化蛹率和羽化率。单一重金属离子及混合离子处理均能导致花翅摇蚊幼虫口器致畸,表现为上颚前齿断裂,中齿和基齿磨损、缺失,下唇板齿部不规则,下唇板边缘齿与中央齿磨损、断裂、增生、缺失。不同重金属离子处理下幼虫口器致畸率不同,并与暴露时间呈正相关,其中1：2配比处理14 d致畸率达到40.61%。重金属离子在摇蚊幼虫体内产生生物富集效应,单一重金属离子处理下的Pb²⁺富集含量7 d至14 d由11.46 mg/kg上升至31.32 mg/kg,不同配比混合离子处理下Pb²⁺富集含量均呈增加趋势,其中1：2配比处理组由15.48 mg/kg上升至42.50 mg/kg,而Cd²⁺在单一重金属与1：1混合离子处理组7 d至14 d的富集含量无显著性变化,2：1配比处理组由14.20 mg/kg下降至9.52 mg/kg,1：2配比由5.85 mg/kg上升至20.99 mg/kg。这些研究结果表明Cd²⁺和Pb²⁺胁迫影响花翅摇蚊幼虫生长发育且口器出现畸型,与重金属在幼虫体内的富集密切相关,为研究重金属对水生生态系统多重效应提供了理论依据。     

Effects of Heavy Metals on Stomatal Movements in Broad Bean Leaves

How do heavy metals affect stomatal movements and whether water channels are involved in stomatal movements was investigated in broad bean (Vicia faba L.) leaves. Three-week old fully expanded leaves were harvested. Leaf epidermis was peeled off and soaked in the Mes–KOH buffer containing the salts of heavy metals. Stomatal aperture was measured under the microscope. The tested heavy metal ions, such as Hg²⁺, Pb²⁺, Zn²⁺, and La³⁺, partly inhibited stomatal opening in light or closing in darkness at submillimolar concentrations, while K⁺, Na⁺ and Mg²⁺ had no visible effects on stomatal movements. As compared to La³⁺, Hg²⁺ affected stomatal movements more significantly. Stomatal movements were almost completely inhibited under a combined Hg²⁺ and La³⁺ treatment. Apparently, La³⁺, a Ca²⁺ channel blocker, inhibits the changes in the cytosolic Ca²⁺ concentration in guard cells, thus affecting stomatal movements. The inhibitory effect of Hg²⁺ on stomatal movements may be explained by the inhibition of water channels. Like Hg²⁺, Zn²⁺ and Pb²⁺ interfered with stomatal movements. It is concluded that heavy metals at submillimolar concentrations inhibit stomatal movements. They may affect water fluxes through guard cell membranes in different ways, i.e., Hg²⁺, Pb²⁺, and Zn²⁺ inhibit water channels, whereas La³⁺ block ion channels. Water channels may be involved in stomatal movements by regulating water fluxes and play a dominant and primary role in stomatal movements.     

Effect of the synthetic growth regulator Cytodef and heavy metals on oxidative status in cucumber plants

We studied the influence of a synthetic cytokinin-like growth regulator (Cytodef) and heavy metal ions—Pb²⁺, Sr²⁺, Zn²⁺, and Ni²⁺—on generation of superoxide anion (O₂^⊙−), lipid peroxidation, and carotenoids content in leaves of 7-day-old cucumber plants (Cucumis sativus L., cv. Izyashchnyi). In some instances Cytodef reduced the toxicity of heavy metals: it mitigated the negative effect of metals on oxidative processes and elevated the concentration of antioxidants (carotenoids).     

Display of lead-binding proteins on Escherichia coli surface for lead bioremediation

Cell surface display of heavy metal-binding proteins has been used to enhance the adsorption capacity of heavy metals and the engineered microbial cells can be potentially used for the bioremediation of heavy metals. In this study, the proteins PbrR, PbrR691, and PbrD from the Cupriavidus metallidurans strain CH34 were displayed on the extracellular membrane of Escherichia coli BL21 cells, with the N-domain of ice-nucleation protein as the anchor protein to achieve specific adsorption of lead ions (Pb²⁺) and bioremediation of lead in the soil. The localization of fusion proteins was confirmed by western blot analysis. We investigated the effects of fusion pattern, expression level, heavy metal concentration, and the presence of other heavy metal ions on the adsorption of Pb²⁺ by these engineered bacteria, and the optimal linker peptide (flexible linker) and inducer concentration (0.5 mM) were obtained. The engineered bacteria showed specific selectivity and strong adsorption capacity for Pb²⁺. The maximum Pb²⁺ adsorption capacity of strains displaying the three proteins (PbrR, PbrR691, and PbrD) were 942.1-, 754.3-, and 864.8-μmol/g cell dry weight, respectively, which was the highest reported to date. The engineered E. coli bacteria were also applied to Pb²⁺-contaminated soil and the detoxification effects were observed via the seed germination test and the growth of Nicotiana benthamiana in comparison with the control BL21, which provides the proof-of-concept for in situ remediations of Pb²⁺-contaminated water or soil.     

Ethylene glycol tetra-acetic acid and salicylic acid improve anti-oxidative ability of maize seedling leaves under heavy-metal and polyethylene glycol 6000-simulated drought stress

Stress caused by divalent heavy metal ions and drought exert many toxic and adverse effects on seedling growth and development of plants, especially on leave growth. Organic acids such as ethylene glycol tetra-acetic acid (EGTA) and salicylic acid (SA) have been shown to alleviate the unfavorable effects exerted by these stresses on seedling growth and metabolism. In order to reveal the physiological mechanism underlying these toxic effects and the alleviated effects exerted by organic acids, maize seedling leaves (genotype “Zhengdan958”) were exposed for 7 days to different concentrations of cadmium (Cd²⁺), mercury (Hg²⁺), and lead (Pb²⁺) ions and to the drought stress-inducing polymer polyethylene glycol (PEG) 6000. The same experiments were also carried out in the presence of EGTA or SA. Treated leaves were analyzed for activities of the anti-oxidative enzymes catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) and for the content of malondialdehyde (MDA). The results showed that stress treatments with the heavy metals Cd²⁺, Hg²⁺, and Pb²⁺ and with PEG all affected the activities of CAT, POD, and SOD, although the extent and patterns of these changes were different under different stress conditions. Both heavy metal and drought stress caused a concentration-dependent increase in MDA content. Treatments in the presence with EGTA or SA showed that both these compounds exerted certain alleviative effects on seedling growth under Cd²⁺, Hg²⁺, and Pb²⁺ stresses and PEG-simulated drought stress, with SA generally showing better effects than EGTA.     

Modulation of Na+ transport across leech skin by pesticides and heavy metals

The aim of the present study was to investigate the effects of environmental pollutants, such as heavy metals and pesticides on ion transport across the skin of the leech (Hirudo medicinalis). We wanted to examine the suitability of this epithelium as a model system for studies concerning the mechanisms of toxic action caused by environmental pollutants. For this purpose we performed Ussing chamber experiments to test three representative heavy metals and pesticides, respectively, for their effects on current flow across leech dorsal integument. Two representatives of each substance class showed distinct effects on ion transport across this epithelium. The heavy metal ions Pb²⁺ and Hg²⁺ produced a significant inhibition of amiloride-sensitive Na⁺ transport across leech skin in concentrations below or close to their limiting values in waste water. Therefore, it seems feasible to use leech skin for future investigations of the toxic actions of these heavy metals. The fact that Pb²⁺ and Hg²⁺ exerted their effects only when applied apically points to a specific action of these divalent cations on ion channels in the apical membrane. However, this inhibition does not seem to be a general feature of divalent cations because Cd²⁺ did not influence ion transport across leech skin at all. Since current flow through amiloride-sensitive Na⁺ channels in typical vertebrate tight epithelia is stimulated by numerous divalent cations, the pronounced inhibition of amiloride-sensitive Na⁺ channels in leech skin by Pb²⁺ and Hg²⁺ might lead to a further differentiation of amiloride-sensitive Na⁺ channels. The two widespread pesticides lindane and promecarb exerted their effects only at comparativ high concentrations. This low sensitivity restricts the usefulness of leech skin as a subject for further analysis of toxicity mechanisms, at least for these two pesticides.     

Development of a fluorescent transgenic zebrafish biosensor for sensing aquatic heavy metal pollution

We report a transgenic zebrafish (Danio rerio) designed to respond to heavy metals using a metal-responsive promoter linked to a fluorescent reporter gene (DsRed2). The metallothionein MT-Ia1 promoter containing metal-responsive elements was derived from the Asian green mussel, Perna viridis. The promoter is known to be induced by a broad spectrum of heavy metals. The promoter-reporter cassette cloned into the Tol2 transposon vector was microinjected into zebrafish embryos that were then reared to maturity. A transgene integration rate of 28 % was observed. The confirmed transgenics were mated with wild-type counterparts, and pools of F₁ embryos were exposed to sub-lethal doses of Cd²⁺, Cu²⁺, Hg²⁺, Pb²⁺ and Zn²⁺. The red fluorescence response of zebrafish embryos was observed 8 h post- exposure to these sub-lethal doses of heavy metals using a fluorescence microscope. Reporter expression estimated by real-time PCR revealed eightfold, sixfold and twofold increase on exposure to highest concentrations of Hg²⁺, Cd²⁺ and Cu²⁺, while Pb²⁺ and Zn²⁺ had no effect. This biosensor could be a first-level screening method for confirming aquatic heavy metal bio-toxicity to eukaryotes.     

Cu,Zn-superoxide dismutase is differently regulated by cadmium and lead in roots of soybean seedlings

The cadmium (Cd²⁺) and lead (Pb²⁺)-induced changes in Cu,Zn-SOD gene expression on the level of mRNA accumulation and enzyme activity were analyzed in roots of soybean (Glycine max) seedlings. The Cd²⁺ caused the induction of copper–zinc superoxide dismutase (Cu,Zn-SOD) mRNA accumulation, at each analyzed metal concentration (5–25 mg/l), whereas in Pb²⁺-treated roots this effect was observed only at the medium metal concentrations (50–100 mg/l of Pb²⁺). The analysis of Cu,Zn-SOD activity proved an increase in enzyme activity during Cd²⁺/Pb²⁺ stresses, however in Pb²⁺-treated plants the activity of enzyme was not correlated with respective mRNAs level. Presented data suggest that different metals may act on various level of Cu,Zn-SOD expression in plants exposed to heavy metals stress.     

Effect of Microwave Radiation on Immobilization of Heavy Metals in Sediment Sludge

In order to evaluate the effect of microwave radiation on immobilization of heavy metals (Cu ^{2 +} , Cr ^{6 +} , Zn ^{2 +} and Pb ^{2 +} ) in sediment sludge, leaching tests were run under different test conditions to compare microwave radiation with conventional blast heating and drying process for their effectiveness in immobilizing heavy metals within sediment sludge. Experimental results indicate that microwave radiation can decrease the concentration of heavy metals in leachate by 63% ～ 70% more than conventional blast heating and drying process in an aclinic shake leaching test. Under the same simulated natural water conditions, the concentration of heavy metals in the leachate using microwave radiation is well below the concentration of heavy metals in leachate using conventional blast heating and drying process. It is therefore concluded that microwave radiation is much more effective than conventional blast heating and drying process in immobilizing heavy metals in sediment sludge.     

Modulation of synaptic events by heavy metals in the central nervous system of mollusks

Summary 1. The effects of heavy metals (Pb²⁺, Hg²⁺, and Zn²⁺) on synaptic transmission in the identified neural network ofHelix pomatia L. andLymnaea stagnalis L. (Gastropoda, Mollusca) were studied, with investigation of effects on inputs and outputs as wells as on interneuronal connections.2. The sensory input running from the cardiorenal system to the central nervous system and the synaptic connections between central neurons were affected by heavy metals.3. Lead and mercury (10^–5–10^–3 M) eliminated first the inhibitory, then the excitatory inputs running from the heart to central neurons. At the onset of action lead increased the amplitude of the excitatory postsynaptic potentials, but blockade of sensory information transfer occurred after 10–20 min of treatment.4. The monosynaptic connections between identified interneurons were inhibited by lead and mercury but not by zinc. Motoneurons were found to be less sensitive to heavy metal treatment than interneurons or sensory pathways.5. The treatment with Pb²⁺ and Hg²⁺ often elicited pacemaker and bursting-type firing in central neurons, accompanied by disconnection of synaptic pathways, manifested by insensitivity to sensory synaptic influences.6. Zn²⁺ treatment also sometimes induced pacemaker activity and burst firing but did not cause disconnection of the synaptic transmission between interneurons.7. A network analysis of heavy metal effects can be a useful tool in understanding the connection between their cellular and their behavioral modulatory influences.     

径流雨水中溶解性有机质特征演化及其对典型污染物迁移和生物有效性的影响

地表径流污染已经逐渐成为城市面源污染的重要组成部分。其中溶解性有机质DOM (Dissolved organic matter)是有机污染物的主要组成部分。DOM中因为含有大量不饱和结构、官能团,其中包括羟基、羧基、羰基、胺基等,这些结构容易与径流中重金属结合发生络合反应,改变重金属的赋存形态,从而对其迁移转化及其生物有效性产生很大的影响。本文以北京市地表径流为研究对象,研究城市地表径流在冬、夏季不同功能区不同下垫面中溶解性有机质特征及其与典型重金属的作用机制,通过荧光淬灭滴定实验,研究夏季径流雨水中DOM的不同组分与重金属Cu~(2+)、Pb~(2+)、Zn~(2+)之间的结合机制。研究结果显示PARAFAC将获得的样品都分解成2类6个不同的组分,1种腐殖酸,1种类蛋白;类蛋白物质的荧光强度与Cu~(2+)、Pb~(2+)的淬灭率要强于腐殖酸,而Zn~(2+)则呈现相反趋势;通过使用二维相关同步光谱发现DOM对重金属Cu~(2+)、Pb~(2+)、Zn~(2+)的敏感性呈现递减趋势,二维相关异步光谱发现Cu~(2+)、Pb~(2+)会先与位于270—300nm附近类蛋白光谱带反应,Zn~(2+)则会先与330nm附近的腐殖酸光谱带反应。     

Enhanced heavy metal immobilization by a bacterial-chitosan complex in soil

Soil contaminated with heavy metals (e.g., Pb²⁺, Cu²⁺, and Zn²⁺) was treated with aminopoly-saccharide chitosan alone or a strain of the bacterium Bacillus subtilis to determine their effects on metal ion accumulations. Phosphatase and Chitosanase production were also assayed. The combined bacterial-chitosan treatment showed the greater accumulation of Zn²⁺ followed by Cu²⁺ as compared to single treatments, while Pb²⁺ did not show a marked accumulation by either single or combined treatments.     

Enhanced heavy metal immobilization by a bacterial-chitosan complex in soil

Soil contaminated with heavy metals (e.g., Pb²⁺, Cu²⁺, and Zn²⁺) was treated with aminopoly-saccharide chitosan alone or a strain of the bacterium Bacillus subtilis to determine their effects on metal ion accumulations. Phosphatase and Chitosanase production were also assayed. The combined bacterial-chitosan treatment showed the greater accumulation of Zn²⁺ followed by Cu²⁺ as compared to single treatments, while Pb²⁺ did not show a marked accumulation by either single or combined treatments.     

Rat kidney epithelial cell culture for metal toxicity studies

Summary Evaluation of the potential adverse human health effects of low-level chronic exposure to heavy metals is dependent on the basic knowledge of the cellular and molecular toxicology of these metals. The use of various cell culture systems has greatly facilitated our knowledge of the cellular effects. Inasmuch as most of the acute and chronic toxic effects of metals occur primarily on the renal proximal tubules, the development of a rat kidney epithelial cell culture has provided a unique system to study the uptake and mechanism of toxicity of metals and their intracellular binding ligands. In the presence ofd-valine, fibroblast growth was retarded and a primary epithelial monolayer culture was selectively grown from rat kidney cells. A distinct difference in the uptake of chemically similar divalent metals, such as Pb²⁺, Hg²⁺, Cd²⁺, and Zn²⁺, was observed in these cells. Both Pb²⁺ and Hg²⁺ were more avidly taken up by kidney cells than Cd²⁺ and Zn²⁺ salts and they also showed increased toxicity. On the other hand, the cellular uptake of Cd from cadmium-metallothionein (CdMT) was much less than from CdCl₂, but CdMT was about seven times more toxic than CdCl₂ when added to the renal cell culture. The cytotoxicity of CdCl₂ was decreased significantly with pretreatment of the cells with CdCl₂, although this had no effect on the toxicity of CdMT. The cellular toxicity of CdMT occurred probably during the process of its transport across the plasma membrane whereas that of CdCl₂ occurred after it had entered the cell. Thus rat kidney epithelial cells may be a useful tool to study the mechanism of renal toxicity of environmental chemicals and drugs. This work was funded by grants-in-aid of research from the Kidney Foundation of Canada.     

Changes in lipid composition in the tissues of fresh-water plant <Emphasis Type="Italic">Hydrilla verticillata</Emphasis> induced by accumulation and elimination of heavy metals

Qualitative and quantitative composition of lipids was investigated in fresh-water vascular plant Hydrilla verticillata (L. fil.) Royle in the course of the accumulation and elimination of heavy metals (HM). The plants were incubated in 100μM solutions of metal nitrates for 10 days. The accumulation of Cu²⁺, Zn²⁺, and Pb²⁺ and their elimination from the plants depended on the duration of exposure and chemical nature of the metal. Accumulation of lead and copper salts was the greatest on the 3rd day, and zinc, on the 10th day. It was associated with changes in the composition of total lipids, polar lipids, and fatty acid (FA). Copper ions suppressed lipid metabolism stronger than other metals. Zn²⁺ and Pb²⁺ induced the accumulation of biomass and elevated the content of some phospholipids and glycolipids. The detected changes (decrease or increase) were observed both during the incubation with HM and within an afterstress period when the plants recovered in the medium free of metals. Judging by their effect on the content of lipids and FA, HM form a series: Cu²⁺ > Zn²⁺ > Pb²⁺. The responses of plant lipid metabolism to the metals of various chemical nature are discussed.     

Pb tolerance and bioaccumulation by the mycelia of Flammulina velutipes in artificial enrichment medium

Mushrooms have the ability to accumulate high concentrations of heavy metals, which gives them potential for use as bioremediators of environmental contamination. The Pb²⁺ tolerance and accumulation ability of living mycelia of Flammulina velutipes were studied in this work. Mycelial growth was inhibited when exposed to 1 mM Pb²⁺. The colony diameter on solid medium decreased almost 10% compared with the control. Growth decreased almost 50% when the Pb²⁺ concentration increased to 4 mM in the medium, with the colony diameter decreasing from 80 mm to 43.4 mm, and dry biomass production in liquid cultures decreasing from 9.23±0.55 to 4.27±0.28 g/L. Lead ions were efficiently accumulated in the mycelia. The amount of Pb²⁺ in the mycelia increased with increasing Pb²⁺ concentration in the medium, with the maximum concentration up to 707±91.4 mg/kg dry weight. We also show evidence that a large amount of the Pb²⁺ was adsorbed to the mycelial surface, which may indicate that an exclusion mechanism is involved in Pb tolerance. These results demonstrate that F. velutipes could be useful as a remediator of heavy metal contamination because of the characteristics of high tolerance to Pb²⁺ and efficient accumulation of Pb²⁺ ions by the mycelia.     

沉水植物菹草在低温条件下对重金属Cu、Pb、Zn的吸附和富集

在10℃的较低温度条件下,研究了冬春季节生长旺盛的沉水植物菹草(Potamogeton crispus L.)对重金属离子Cu²⁺,Pb²⁺,Zn²⁺的生物吸附特征及解吸情况,对不同初始浓度重金属水体中的重金属离子去除率情况,以及在此过程中菹草各器官(叶、茎、根茎、根)对重金属离子的富集情况。结果表明,菹草对Cu²⁺,Zn²⁺的吸附在20 min内达到平衡,对Pb²⁺的吸附在50 min内达到平衡,吸附动力学结果符合伪二级动力学方程,决定系数分别达1,1,0.997 8。Freundlich等温线可较好地拟合菹草吸附Cu²⁺,Pb²⁺,Zn²⁺的过程,Cu²⁺,Pb²⁺,Zn²⁺的吸附容量分别达到66.900 6,26.543 0,30.371 8 mg·L^-1。以去离子水作洗脱剂,解吸液中3种重金属离子浓度均低于仪器检出限(0.01 mg·L^-1),解吸程度微弱。投放菹草后,随着初始处理浓度的升高,水体Cu²⁺的去除率先降低后升高,Pb²⁺的去除率的变化趋势与Cu²⁺类似。Zn²⁺去除率则随水体Zn²⁺初始浓度的升高而逐渐升高。菹草各器官对水体3种重金属离子的富集能力不同,排序为Cu²⁺＞Zn²⁺＞Pb²⁺。不同器官对同一种重金属离子的富集量差异显著,叶是富集重金属离子的主要器官。水体重金属离子的初始浓度会影响菹草各器官富集重金属离子的能力,一般随水体重金属初始浓度升高,菹草各器官的重金属离子富集量虽有不同程度的增加但富集系数持续减小。     

Interaction Between Metals and Chelating Agents Affects Glutamate Binding on Brain Synaptic Membranes

The present study investigates the possible effects of Hg²⁺, Pb²⁺, and Cd²⁺ on [³H]-glutamate binding. To better understand the role of the thiol-disulfide status on the toxicity of such metals toward glutamatergic neurotransmission, we used three thiol chelating agents, 2,3-dimercaptopropanol (BAL), 2,3-dimercaptopropane 1-sulfonate (DMPS), and meso-2,3-dimercaptosuccinic acid (DMSA). Dithiotreitol (DTT) was tested for its ability to prevent metals-induced inhibition on [³H]-glutamate binding. Hg²⁺, Pb²⁺, and Cd²⁺ showed a concentration-dependent inhibition on [³H]-glutamate binding, and mercury was the most effective inhibitor. BAL did not prevent [³H]-glutamate binding inhibition by Hg²⁺, Cd²⁺, and Pb²⁺. However, DMPS and DMSA prevented the inhibition caused by Cd²⁺ and Pb²⁺, but not by Hg²⁺. DTT did not prevent the inhibition on [³H]-glutamate binding caused by 10 M Hg²⁺. In contrast, it was able to partially prevent [³H]-glutamate binding inhibition caused by 40 M Pb²⁺ and Cd²⁺. These results demonstrated that the heavy metals present an inhibitory effect on [³H]-glutamate binding. In addition, BAL was less effective to protect [³H]-glutamate binding inhibition caused by these metals than other chelating agents studied.