Excess Nickel Research Articles

Antioxidative-related enzyme activity in Alyssum markgrafii shoot cultures as affected by nickel level

Shoot cultures of rare Balkan hyperaccumulating species Alyssum markgrafii were subjected to high nickel concentrations of 1, 3, 5, and 8 mM. The effects of graded nickel concentrations on toxicity, pigments, and several components of plant antioxidative defense system were characterized. Toxic effects of excess nickel were observed through slower growth and biomass decrease, together with increased reactive oxygen species (ROS) production and lipid peroxidation. Nickel exposure decreased chlorophyll a, b, total chlorophyll as well as carotenoid concentration. Addition of sodium benzoate, potent ROS scavenger, showed concentration-dependent disturbing effect on nickel hyperaccumulation, lowering the content of accumulated nickel in A. markgrafii shoots. General reducing power represented by low molecular weight antioxidants and phenols was inversely correlated with nickel concentration. Among the investigated antioxidative enzymes, POD seems to play important role in ROS level regulation upon excessive nickel in medium.

Order/disorder in YbNi1±xGa2∓x (x ≤ 0.08): Crystal structure, thermal expansion and magnetic properties

The ternary phase YbNi1±xGa2∓x (x ≤ 0.08) has been synthesised from the elements by high-frequency melting in argon atmosphere with subsequent annealing at 600 °C or 800 °C. From X-ray powder and single crystal diffraction investigations the phase is found to be isotypic with MgCuAl2: space group Cmcm, Z = 4, a = 4.0987–4.1147 Å, b = 9.8516–9.8620 Å, c = 6.5995–6.5916 Å for the specimens annealed at 800 °C. The quantum chemical analysis of atomic interactions in YbNiGa2 shows Ga and Ni forming a network polyanion with covalent bonds, while ytterbium cations are located within the cavities of the polyanion. From the magnetic susceptibility data and LIII XAS spectra, the 4f13 electronic configuration of ytterbium (Yb3+) was established in samples with nickel excess (comparing to x = 0), whereas an additional small contribution of the 4f14 configuration is found for compositions with the gallium excess. No change in the ytterbium valence state was detected down to 5 K. In situ low- and high-temperature powder diffraction investigations applying both X-ray synchrotron radiation and neutrons revealed no change in structure within the broad temperature range 3.4–1173 K. Both synchrotron and neutron diffraction data show smooth, but strongly anisotropic variation of lattice parameters below 200 K: the thermal contraction ratio in [100], [010] and [001] directions is 4.5:3.2:1. The temperature dependence of atomic displacement parameters indicates a certain amount of static disorder for all atomic species in the crystal. At least two distinct sites with varying charge distributions in the vicinity of the Ga atoms are confirmed by 69,71Ga NMR spectroscopy.

Metal–silicate partitioning of Ni and Co in a deep magma ocean

The pattern of siderophile (iron-loving) element abundance in the silicate portion of the Earth is a consequence of metal separation during core formation. The apparent excess of nickel and cobalt in mantle-derived rocks has been attributed to metal-silicate equilibration in a deep terrestrial magma ocean. Based on the extrapolation of phase equilibria and metal-silicate partitioning results obtained at lower pressure (P) and temperature (T), previous estimates of the P–T of equilibration are all greater than 25GPa and 3000K. Using the laser-heated diamond anvil cell, we have extended metal–silicate partitioning measurements for Ni and Co to 75GPa and 4400K, exceeding the liquidus temperatures for both metal and silicate (basalt or peridotite) and, therefore, achieving thermodynamic conditions directly comparable to those of the magma ocean. The metal–silicate partition coefficients of nickel and cobalt decrease with increasing pressure and reach the values required to yield present mantle concentrations at ~50GPa. At these conditions, silicon and oxygen concentrations measured in the metallic liquid allow to solve the seismically constrained core density deficit. Above 60GPa, the partition coefficients become too low, resulting in an overabundance of Ni and Co in the silicate mantle. Our data therefore support the paradigm of core formation in a deep mama ocean, providing an upper bound for the depth at which Earth's core may have formed, and explaining the main geophysical (density) and geochemical (excess siderophile elements) observables.

One-step solvothermal synthesis of nickel selenide series: Composition and morphology control

A one-step oleylamine-mediated solvothermal method was reported for the synthesis of nickel selenide series within a short reaction time. The method provided a suitable nucleation and growth environment in a uniform and transparent solution reaction system. Through adjustment of the Ni/Se raw material ratio and reaction temperature, cubic NiSe2, orthorhombic NiSe2, and hexagonal Ni1−xSe (x = 0–0.15) were obtained. In addition, under an excess nickel source (Ni : Se = 2 : 1) and phase change agent, hexagonal NiSe was converted to rhombohedral Ni3Se2, in which the intermediate phase (NiSe) acted as both reactant and template, plus an effect on Ni3Se2 morphology. At a certain reaction temperature of 260 °C, the phase transformation and morphology can be adjusted by changing the solvents (mixture of OLA and ODE). Finally, the conversion mechanism from cubic NiSe2 to orthorhombic NiSe2 at different reaction temperatures was investigated, and the formation process of a nickel selenide series had also been studied through synthetic route controlled experiments. This paper provided a simple and low cost method to control the composition and morphology of nickel selenide series, which would be of great potential for the synthesis of other metal selenides.

Excessive nickel release from mobile phones-a persistent cause of nickel allergy and dermatitis

Despite the political intention to limit nickel allergy and dermatitis in Europeans, nickel allergy remains frequent. There are several explanations for the persistence of nickel allergy and dermatitis, including the increasing use of mobile phones. Before regulation of nickel release from mobile phones, we showed that eight (19.5%) of 41 mobile phones marketed in Denmark between 2003 and 2007 released nickel in concentrations that may result in nickel allergy and dermatitis. In 2009, the EU Nickel Directive was revised to include nickel-releasing mobile phones. To investigate the proportion of mobile phones sold in Denmark that release nickel after regulation. Metallic parts from 50 randomly selected mobile phones currently for sale in Denmark were tested for nickel release by use of the dimethylglyoxime (DMG)-nickel spot test. Nine (18%) phones showed at least one positive DMG test reaction and two phones had more than one DMG test-positive spot. Apparently, the proportion of mobile phones with significant nickel release remains unchanged, despite the 2009 revision of the EU Nickel Directive. We encourage manufacturers to measure nickel release from metallic components used in the assembly of mobile phones to ensure safe products.

Nickel and cobalt allergy before and after nickel regulation – evaluation of a public health intervention

Over the 20th century, the frequent use of nickel in consumer products resulted in an increasing prevalence of nickel allergy. Risk items included suspenders in the 1950s-1960s; buttons, zippers and rivets in the 1970s; and ear-piercing jewellery in the 1980s. When subjects allergic to nickel were exposed to nickel in high concentrations, it often resulted in allergic nickel contact dermatitis and hand eczema. In 1990, the Danish government began to regulate consumer nickel exposure as a response to the increasing nickel allergy problem. In 1994, the EU Nickel Directive was passed, a regulation that was based on the Danish and Swedish nickel regulations. These major public health interventions were expected to change the epidemiology of nickel allergy and dermatitis in Europe. Furthermore, it was debated whether nickel would be replaced by cobalt in inexpensive jewellery and result in higher prevalence of cobalt allergy. An evaluation of the possible effects of the European nickel regulations is of importance to ensure protection of consumers and dermatitis patients. This doctoral thesis aimed to evaluate the effects of regulatory interventions on nickel exposure by investigating the development of nickel allergy and dermatitis before and after nickel regulation. Furthermore, a change in the association between nickel allergy and hand eczema was evaluated. The nickel spot test was validated to determine its value when used for screening purposes. Possible explanations for the persistence of nickel allergy were explored including genetic predisposition and consumer nickel exposure from jewellery and accessories. A cobalt spot test was developed and validated. Finally, it was evaluated whether a cobalt allergy epidemic had replaced the nickel allergy epidemic after nickel regulation in terms of increasing cobalt sensitization and cobalt exposure. The thesis showed that the prevalence of nickel allergy decreased significantly after nickel regulation in young Danish women from the general population (18-35 years) and in young Danish female dermatitis patients from a university patch test clinic (0-30 years). Stratification by ear-piercing status revealed that women ear pierced before 1990 had a significantly higher prevalence of nickel allergy and dermatitis than women ear pierced after 1990. Furthermore, the association between hand eczema and nickel allergy decreased in young women aged 18-35 years when a comparison was made between women who were patch tested and questioned in, respectively, 1990 and 2006. Despite the decreasing prevalence of nickel allergy, this condition remains prevalent in young Danish women, as about 10% are nickel allergic. Genetic predisposition to nickel allergy was evaluated by investigating the possible association between filaggrin null mutation status and nickel allergy. A positive association was found but it was also concluded that environmental nickel exposure is of much greater importance. Thus, of 354 consumer items purchased from 36 different stores in Copenhagen, 22% released nickel in concentrations that may result in nickel dermatitis in sensitized subjects. Therefore excessive consumer nickel exposure remains common in Denmark and may be an important explanation for the persistence of nickel allergy. Excessive nickel release was also frequent when samples of earrings purchased in Warsaw and London were examined with the nickel spot test, in particular earrings purchased from street markets and shops with independent ownership. Only very weak indications of an emerging cobalt allergy epidemic were found, as the prevalence of cobalt allergy has not yet increased in young people and only four of 354 consumer items purchased in Copenhagen released cobalt in concentrations that may result in cobalt dermatitis in sensitized individuals. The specificity of the nickel spot test was 98% and the sensitivity 59%. Also, a cobalt spot test was developed and validated and seemed to be a useful diagnostic tool. In conclusion, the Danish nickel regulation and the EU Nickel Directive have changed the epidemiology of nickel allergy in Denmark. However, the Nickel Directive and its reference methods need to be revised to better protect consumers and dermatitis patients.

Nikelin ıspanakta (Spinacia oleracea) çimlenme ve bazı fide büyüme parametreleri üzerine etkisi

This research was conducted to define the effect of excess nickel on germination and some growth parameters of early seedling period in spinach (Spinacia oleracea). For this aim, concentrations were 0 (control), 25, 50, 100, 200, 400 and 800 mg L-1 Ni in germination stage and 0 (control), 2.5, 5, 10, 20, 40 and 80 mg L-1 Ni in early seedling stage. Nickel was stimulator for germination stage in 25 mg L-1 and early seedling stage in 2.5 mg L-1; but it was inhibitor for germination, radicula-hypocotyll growth, growth tolerance index and water content of radicle-hypocotyll in higher concentrations. In study, nickel was toxic for germination stage than the early seedling stage in higher concentrations, because it is estimated that the barrier effects of seed coat can be reason of this event.

Effect of Ultrasound on the Performance of Nickel Hydrazine Electroless Plating Baths

This article addresses the relationship between morphology of metallic skin layer and process parameters of hydrazine-based electroless plating baths during the fabrication of nickel-ceramic microfiltration membranes. While process performance was evaluated in terms of overall conversion and metal plating efficiency, the film morphology was characterized in terms of average metal film thickness, pore size, and percent pore densification. Sonication was considered as an additional degree of freedom to the conventional electroless plating process. Process parameters varied include initial nickel solution concentration (0.04–0.16 mol/L), loading ratio (196 and 393 cm2/L), and relevant mass transfer coupling (sonication). It was observed that sonication assisted electroless plating provided the best combination of both process as well as performance characteristics in comparison with the base case and membrane stirred cases. Ultrasound was found to enhance the selective conversion by more than 50% compared to the other cases. About 50–100% excess nickel plating rate was evaluated for the sonication assisted case due to which the membranes with pore size as low as 11 nm were achieved.

Synthesis and characterization of LiNi0.43Mn0.43Co0.13O2 by wet-chemical method

In the aim to obtain a new powder able to substitute oxide intensively used as a material for the positive electrode in the batteries Lithium-ion, the LiNi0.43Mn0.43Co0.13O2 material was synthesized by sol–gel method and characterized by XRD, RAMAN and TEM. The composition of our LiNi0.43Mn0.43Co0.13O2 oxide was checked by ICP analysis. The Rietveld refinement showed a very weak mixing cation disorder, probably due to the presence of nickel excess in this material. Electrochemical performances of LiNi0.43Mn0.43Co0.13O2 oxide were tested using this material as positive electrode in a battery of lithium.

A chemical test of the principle of critical point universality: The solubility of nickel (II) oxide in isobutyric acid + water near the consolute point

A mixture of isobutyric acid + water has an upper consolute point at 38.8 mass % isobutyric acid and temperature near 26 °C. Nickel (II) oxide dissolves in this mixture by reacting with the acid to produce water and nickel isobutyrate. The solubility of nickel (II) oxide in isobutyric acid + water has been measured as a function of temperature at compositions, 25, 38.8, and 60 mass % isobutyric acid. For values of the temperature, T, which were at least 2 K in excess of the liquid-liquid phase transition temperature, the measured values of the solubility, s, lie on a straight line when plotted in van't Hoff form with ln s versus 1∕T. The slope, (∂ln s∕∂(1∕T)), of the line is negative indicating that the dissolution reaction is endothermic. When the temperature was within 2 K of the phase transition temperature, however, (∂ln s∕∂(1∕T)) diverged toward negative infinity. The principle of critical point universality predicts that when excess solid nickel (II) oxide is in dissolution equilibrium with liquid isobutyric acid + water, (∂ln s∕∂(1∕T)) should diverge upon approaching the consolute point along the critical isopleth at 38.8 mass % isobutyric acid. As determined by the sign of the enthalpy of solution, the sign of this divergence is expected to be negative. Not only do our experiments confirm these predictions, but they also show that identical behavior can be observed at both 25 and 60 mass % isobustyric acid, compositions which lie substantially to either side of the critical composition.

Combinatorial performance characteristics of agitated nickel hypophosphite electroless plating baths

In this article, we present the combinatorial performance characteristics of agitated sodium hypophosphite electroless plating baths. Various performance characteristics assessed include bath conversion, plating efficiency, selective conversion, metal film thickness, average pore size, effective porosity and percent pore densification (PPD). Bath agitation was brought forward by rotating a symmetric disk shaped porous ceramic substrate with a nominal pore size of 275 nm. The plating characteristics were investigated for wide range of nickel solution concentrations (0.04–0.16 mol/L), stirrer speed (0–200 rpm) and for two different loading ratios (defined as substrate surface area per unit volume of plating solution) values (196 and 393 cm 2/L). It was evaluated that stirring had a profound effect on sodium hypophosphite based electroless nickel baths, which are characterized with lower conversions (10–39%) and higher plating efficiencies (62–99%) without stirring phenomena. The stirred plating baths provided about 20–56% excess nickel plating rate when compared to the baths without stirring. This lead to a reduction in average membrane pore size by 20–42 nm and an enhancement in percent pore densification values by about 2–7%. Further, higher concentrations as high as 0.16 mol/L have been found to be detrimental to reduce the metal plating efficiency to lower values (42%). Observed data trends confirm upon the urgent need to identify suitable mass transfer enhancement techniques that target enhancement in selective conversion while providing good values of plating efficiency and PPD.

The characteristics of placental transfer and tissue concentrations of nickel in late gestational rats and fetuses

The dynamics of nickel (Ni) uptake, transfer, retention and clearance in fetuses and late gestational rats were investigated by assessing its distributions in placenta, maternal and fetal organs and tissues during the 24 h period after a single dose of 63Ni intraperitoneal injection on gestational day 20. Peak 63Ni radioactivity was detected at 0.5 h in maternal blood, at 3 h in placenta, fetal membranes, fetal blood, fetal heart, maternal kidney, lung, stomach, liver and brain, at 9 h in fetal kidney, stomach, liver and brain, and lastly at 24 h in fetal lung and amniotic fluid. The maximal 63Ni radioactivity among all samples was detected consistently in the fetal membranes and placenta. The 63Ni radioactivity in fetal blood was higher than that in maternal blood from 3 to 24 h. The fetal liver, heart, stomach and brain exhibited higher 63Ni radioactivity than the corresponding maternal organs from 6 to 24 h. However, maternal kidney consistently exhibited significantly higher 63Ni radioactivity than the fetal kidney. The 63Ni in fetal lung and amniotic fluid increased throughout the period of experimental observation. These observations corroborated previous finding that nickel is actively transferred across the blood-placenta-barrier into fetus, but hardly from fetus to mother. Moreover, these results suggest that the placenta has a high affinity for nickel and its barrier does not protect the fetus from nickel exposure. The fact that nickel concentrations are higher in most fetal organs and tissues than in corresponding maternal organs and tissues in late gestation indicates that, unlike the dam, fetuses lack effective means for getting rid of excessive nickel due to its confined environment and relatively weak kidney functions. The situation is exacerbated by mother-to-fetus unidirectional transfer. Consequently, the fetuses are particularly vulnerable to the damaging effects of nickel.

Changes in photosynthesis, mesophyll conductance to CO 2, and isoprenoid emissions in Populus nigra plants exposed to excess nickel

Poplar ( Populus nigra) plants were grown hydroponically with 30 and 200 μM Ni (Ni 30 and Ni 200). Photosynthesis limitations and isoprenoid emissions were investigated in two leaf types (mature and developing). Ni stress significantly decreased photosynthesis, and this effect depended on the leaf Ni content, which was lower in mature than in developing leaves. The main limitations to photosynthesis were attributed to mesophyll conductance and metabolism impairment. In Ni-stressed developing leaves, isoprene emission was significantly stimulated. We attribute such stimulation to the lower chloroplastic [CO 2] than in control leaves. However chloroplastic [CO 2] did not control isoprene emission in mature leaves. Ni stress induced the emission of cis-β-ocimene in mature leaves, and of linalool in both leaf types. Induced biosynthesis and emission of isoprenoids reveal the onset of antioxidant processes that may also contribute to reduce Ni stress, especially in mature poplar leaves.

Excessive nickel release from earrings purchased from independent shops and street markets – a field study from Warsaw and London

Nickel allergy is frequent and cause morbidity and increased health care costs. The aim of this study was to determine the proportion of inexpensive earrings randomly purchased from stores and street markets in two capitals that gave positive dimethylglyoxime (DMG) test reactions and to determine whether the degree of nickel release was related to shop category. Random inexpensive metallic earrings were purchased from stores and vendors in London and Warsaw. A qualitative investigation of nickel release by using the DMG test was performed. DMG testing revealed that respectively 15.1% (n=205) and 18.4% (n=206) of earrings purchased in London and Warsaw released nickel as indicated by positive test outcomes. Stratification by store category showed that DMG test-positive jewellery were mainly purchased from street markets and from stores that were not part of national or international chains. Despite the EU Nickel Directive having resulted in decreasing prevalence of nickel allergy, a large proportion of inexpensive earrings still release nickel in concentrations that may result in nickel allergy and dermatitis. Authorities should prioritize information campaigns and random inspections as a legislation that is not followed is of limited value.

Structural Basis of Low-Affinity Nickel Binding to the Nickel-Responsive Transcription Factor NikR from Escherichia coli

Escherichia coli NikR regulates cellular nickel uptake by binding to the nik operon in the presence of nickel and blocking transcription of genes encoding the nickel uptake transporter. NikR has two binding affinities for the nik operon: a nanomolar dissociation constant with stoichiometric nickel and a picomolar dissociation constant with excess nickel [Bloom, S. L., and Zamble, D. B. (2004) Biochemistry 43, 10029−10038; Chivers, P. T., and Sauer, R. T. (2002) Chem. Biol. 9, 1141−1148]. While it is known that the stoichiometric nickel ions bind at the NikR tetrameric interface [Schreiter, E. R., et al. (2003) Nat. Struct. Biol. 10, 794−799; Schreiter, E. R., et al. (2006) Proc. Natl. Acad. Sci. U.S.A. 103, 13676−13681], the binding sites for excess nickel ions have not been fully described. Here we have determined the crystal structure of NikR in the presence of excess nickel to 2.6 Å resolution and have obtained nickel anomalous data (1.4845 Å) in the presence of excess nickel for both NikR alone and NikR cocrystallized with a 30-nucleotide piece of double-stranded DNA containing the nik operon. These anomalous data show that excess nickel ions do not bind to a single location on NikR but instead reveal a total of 22 possible low-affinity nickel sites on the NikR tetramer. These sites, for which there are six different types, are all on the surface of NikR, and most are found in both the NikR alone and NikR−DNA structures. Using a combination of crystallographic data and molecular dynamics simulations, the nickel sites can be described as preferring octahedral geometry, utilizing one to three protein ligands (typically histidine) and at least two water molecules.

Fabrication of nickel boride-coated carbon nanotube films by electrophoresis and electroless deposition for electrochemical hydrogen storage

Network-like carbon nanotube (CNT) films free of polymer binder were deposited directly onto a stainless steel substrate by electrophoresis. Results of experiments indicated that a CNT film with duplex surface treatment (nitric acid etching and nickel boride coating) provides satisfactory electrochemical hydrogen storage. Nitric acid treatment increased the hydrogen storage capacity of the CNT film due to the opening of CNTs, the formation of micropores in the CNT surface, and the improvement of surface wettability. Coating the CNT film with nickel boride (Ni 2B) greatly improved the electrochemical activity of the film and consequently increased the hydrogen storage capacity. The optimal amount of nickel boride coating on the CNT film was found to be about 45 wt%. Smaller amounts of nickel boride cannot provide enough electrochemical activity. Excessive nickel boride, on the other hand, leads to a decrease in the number of active sites on CNTs that are available for hydrogen storage.

Assessment of nickel release from earrings randomly purchased in China and Thailand using the dimethylglyoxime test

China and Thailand produce large amounts of jewellery that are sold domestically and abroad. To identify nickel release and metal content in earrings purchased in China and Thailand. A total of 557 earrings were randomly purchased from vendors in 11 markets located in Beijing, Chengdu, Bangkok, Patong Beach, and Hat Yai. Earrings were subjected to dimethylglyoxime (DMG) tests and 26 of the DMG negative earrings were further evaluated qualitatively for major and minor metal content using X-ray fluorescence spectrometry. A total of 314 Chinese earrings (31.5%) and 243 Thai earrings (29.2%) were DMG test positive. Three (11.5%) of 29 DMG negative earrings contained nickel as a major component; 7 (26.9%) of 29 DMG negative earrings contained nickel as a minor component. Excessive nickel release was frequent. This may contribute to the high prevalence of nickel allergy in both countries. Increased public education together with the adoption of a regulatory intervention in Thailand may be warranted. In China, enforcement of the 2002 Chinese National Standard GB 11887 may assist in reducing sensitization. These initiatives may eventually result in decreased morbidity among the Chinese and Thai citizens, but can potentially benefit recipient countries of these important earring producing countries.

Microbial nickel proteins

Microorganisms have evolved to utilize nickel ions in several different enzyme systems that enable these organisms to survive and proliferate in various environments. Typically the biosynthesis of these nickel containing enzymes are multi-step processes involving a number of accessory proteins, with one or more proteins dedicated to the delivery of the cognate nickel ion to the active site of the enzyme. This review highlights the nickel proteins dedicated to the biogenesis of [NiFe]-hydrogenase, urease, and carbon monoxide dehydrogenase, and aims to summarize our current knowledge of these unique proteins. Putative proteins that function in excess nickel storage and/or detoxification, through sequestration of considerable amount of nickel, are also discussed.

Nickel allergy in patch‐tested female hairdressers and assessment of nickel release from hairdressers' scissors and crochet hooks

Hand eczema as well as nickel contact allergy is prevalent among hairdressers. Recently, two female hairdressers were diagnosed with nickel contact allergy-related hand eczema following prolonged skin contact with scissors and crochet hooks used during work. To determine the proportion of hairdressers' scissors and crochet hooks that released an excessive amount of nickel and to determine the prevalence of nickel allergy among patch-tested female hairdressers. Random hairdressers' stores in Copenhagen were visited. The dimethylglyoxime (DMG) test was used to assess excessive nickel release. The prevalence of nickel allergy among female hairdressers from the database at Gentofte Hospital was compared with the prevalence of nickel allergy among other consecutively patch-tested dermatitis patients. DMG testing showed that 1 (0.5%; 95% CI = 0 - 2.0) of 200 pairs of scissors and 7 (53.8%; 95% CI = 26.0 - 82.0) of 13 crochet hooks released an excessive amount of nickel. The prevalence of nickel allergy was higher among middle-aged and older female hairdressers than among young female hairdressers. The prevalence of nickel allergy was lower among young hairdressers in comparison to older hairdressers. This may possibly be a result of the European Union (EU) Nickel Directive or a consequence of a decreased use of nickel-releasing work tools in salons. When nickel allergic hairdressers present with hand eczema, their work tools should be investigated for nickel release.

Interference of nickel with copper and iron homeostasis contributes to metal toxicity symptoms in the nickel hyperaccumulator plant Alyssum inflatum

The divalent cations of several transition metal elements have similar chemical properties and, when present in excess, one metal can interfere with the homeostasis of another. To better understand the role of interactions between transition metals in the development of metal toxicity symptoms in plants, the effects of exposure to excess nickel (Ni) on copper (Cu) and iron (Fe) homeostasis in the Ni hyperaccumulator plant Alyssum inflatum were examined. Alyssum inflatum was hypertolerant to Ni, but not to Cu. Exposure to elevated subtoxic Ni concentrations increased Cu sensitivity, associated with enhanced Cu accumulation and enhanced root surface Cu(II)-specific reductase activity. Exposure to elevated Ni concentrations resulted in an inhibition of root-to-shoot translocation of Fe and concentration-dependent progressive Fe accumulation in root pericycle, endodermis and cortex cells of the differentiation zone. Shoot Fe concentrations, chlorophyll concentrations and Fe-dependent antioxidant enzyme activities were decreased in Ni-exposed plants when compared with unexposed controls. Foliar Fe spraying or increased Fe supply to roots ameliorated the chlorosis observed under exposure to high Ni concentrations. These results suggest that Ni interferes with Cu regulation and that the disruption of root-to-shoot Fe translocation is a major cause of nickel toxicity symptoms in A. inflatum.