Bioinformatic and Expression Analyses of Genes Mediating Zinc Homeostasis in Nostoc punctiforme

Zinc homeostasis was investigated in Nostoc punctiforme. Cell tolerance to Zn²⁺ over 14 days showed that ZnCl₂ levels above 22 μM significantly reduced cell viability. After 3 days in 22 μM ZnCl₂, ca. 12% of the Zn²⁺ was in an EDTA-resistant component, suggesting an intracellular localization. Zinquin fluorescence was detected within cells exposed to concentrations up to 37 μM relative to 0 μM treatment. Radiolabeled ⁶⁵Zn showed Zn²⁺ uptake increased over a 3-day period, while efflux occurred more rapidly within a 3-h time period. Four putative genes involved in Zn²⁺ uptake and efflux in N. punctiforme were identified: (i) the predicted Co/Zn/Cd cation transporter, putative CDF; (ii) the predicted divalent heavy-metal cation transporter, putative Zip; (iii) the ATPase component and Fe/Zn uptake regulation protein, putative Fur; and (iv) an ABC-type Mn/Zn transport system, putative zinc ZnuC, ZnuABC system component. Quantitative real-time PCR indicated the responsiveness of all four genes to 22 μM ZnCl₂ within 3 h, followed by a reduction to below basal levels after 24 h by putative ZIP, ZnuC, and Fur and a reduction to below basal level after 72 h by putative CDF efflux gene. These results demonstrate differential regulation of zinc transporters over time, indicating a role for them in zinc homeostasis in N. punctiforme.     

Evidence for a zinc/proton antiporter in rat brain

The data presented in this paper are consistent with the existence of a plasma membrane zinc/proton antiport activity in rat brain. Experiments were performed using purified plasma membrane vesicles isolated from whole rat brain. Incubating vesicles in the presence of various concentrations of 65Zn2+ resulted in a rapid accumulation of 65Zn2+. Hill plot analysis demonstrated a lack of cooperativity in zinc activation of 65Zn2+ uptake. Zinc uptake was inhibited in the presence of 1 mM Ni2+, Cd2+, or CO2+. Calcium (1 mM) was less effective at inhibiting 65Zn2+ uptake and Mg2+ and Mn2+ had no effect. The initial rate of vesicular 65Zn2+ uptake was inhibited by increasing extravesicular H+ concentration. Vesicles preloaded with 65Zn2+ could be induced to release 65Zn2+ by increasing extravesicular H+ or addition of 1 mM nonradioactive Zn2+. Hill plot analysis showed a lack of cooperativity in H+ activation of 65Zn2+ release. Based on the Hill analyses, the stoichiometry of transport may include Zn2+/Zn2+ exchange and Zn2+/H+ antiport, the latter being potentially electrogenic. Zinc/proton antiport may be an important mode of zinc uptake into neurons and contribute to the reuptake of zinc to replenish presynaptic vesicle stores after stimulation.     

Zinc transport mediated by barley ZIP proteins are induced by low pH

It is estimated that nearly 50% of the world''s population is at risk of zinc (Zn) deficiency. The challenge is therefore to increase the Zn content in edible plant parts in order to improve the nutritional value of staple foods. We recently reported the identification and characterization of three barley genes encoding zinc transport proteins belonging to the ZIP protein family. These proteins are believed to be involved in cellular uptake of Zn²⁺. In this addendum, the Zn²⁺ transport capacity of ZIP proteins isolated from barley roots was investigated in response to various pH levels. We show that a lowering of pH induces a better growth at low Zn²⁺ concentrations of yeast cells expressing ZIP proteins. However, no significant change in transport capacity (V_max) could be observed for HvIRT1, whereas lowering of pH from 5.5 to 4.2 increased the V_max value with 64% for HvZIP5. These results indicate that proton activity has an important role in regulating the Zn²⁺ transport capacity of Zn²⁺ specific ZIP transport proteins. This information will increase the understanding of ZIP proteins and facilitate engineering of genotypes able to grow efficiently on marginal soils.Key words: ZIP proteins, barley, zinc transport, pH     

Expression of a Neurospora crassa zinc transporter gene in transgenic Nicotiana tabacum enhances plant zinc accumulation without co‐transport of cadmium

Zinc (Zn) is an essential micronutrient required for growth and development of all organisms. Deficiency of Zn in humans is widespread, affecting 25% of world population and efforts are underway to develop crop plants with high levels of Zn in their edible parts. When strategies for enhancing Zn in crop plants are designed, it is essential to exclude cadmium (Cd), a toxic analogue of Zn. In the present work, a high affinity and high specificity zinc transporter gene (tzn1) from Neurospora crassa was cloned and introduced into Nicotiana tabacum with the objective of enhancing the potential of plants for zinc acquisition. When grown in hydroponic medium spiked with ⁶⁵Zn, transgenic plants showed enhanced accumulation of Zn (up to 11 times) compared to control plants, which was confirmed further by environmental scanning electron microscopy coupled with Energy Dispersive X‐ray analysis. More importantly, no significant difference in uptake of Cd²⁺, Fe²⁺, Ni²⁺, Cu²⁺, Mn²⁺ and Pb²⁺ between the transgenic and control plants was observed. The present studies have shown that Neurospora crassa tzn1 is a potential candidate gene for developing transgenic plants for improving Zn uptake, without co‐transport of Cd and may have implications in Zn phytofortification and phytoremediation.     

65Zn2+ transport by isolated gill epithelial cells of the American lobster, Homarus americanus

Gills are the first site of impact by metal ions in contaminated waters. Work on whole gill cells and metal uptake has not been reported before in crustaceans. In this study, gill filaments of the American lobster, Homarus americanus, were dissociated in physiological saline and separated into several cell types on a 30, 40, 50, and 80% sucrose gradient. Cells from each sucrose solution were separately resuspended in physiological saline and incubated in ⁶⁵Zn²⁺ in order to assess the nature of metal uptake by each cell type. Characteristics of zinc accumulation by each kind of cell were investigated in the presence and absence of 10 mM calcium, variable NaCl concentrations and pH values, and 100 μM verapamil, nifedipine, and the calcium ionophore A23187. ⁶⁵Zn²⁺ influxes were hyperbolic functions of zinc concentration (1–1,000 μM) and followed Michaelis–Menten kinetics. Calcium reduced both apparent zinc binding affinity (K _m) and maximal transport velocity (J _max) for 30% sucrose cells, but doubled the apparent maximal transport velocity for 80% sucrose cells. Results suggest that calcium, sodium, and protons enter gill epithelial cells by an endogenous broad-specificity cation channel and trans-stimulate metal uptake by a plasma membrane carrier system. Differences in zinc transport observed between gill epithelial cell types appear related to apparent affinity differences of the transporters in each kind of cell. Low affinity cells from 30% sucrose were inhibited by calcium, while high affinity cells from 80% sucrose were stimulated. ⁶⁵Zn²⁺ transport was also studied by isolated, intact, gill filament tips. These intact gill fragments generally displayed the same transport properties as did cells from 80% sucrose and provided support for metal uptake processes being an apical phenomenon. A working model for zinc transport by lobster gill cells is presented.     

Cadmium and zinc influx characteristics by intact corn (Zea mays L.) seedlings

Summary Cadmium and zinc uptake parameters were determined for intact corn (Zea mays L.) seedlings grown for 15 and 22 in nutrient solutions containing levels of Cd and Zn that were similar to those found in soil solutions. Uptake of both elements was assumed to follow Michaelis-Menten kinetics. Calculations were based on the concentrations of free ionic Cd (Cd²⁺) and Zn (Zn²⁺) rather than the total solution concentration. Rates of Zn uptake were measured by determining depletion of Zn for periods of up to 30 h from solutions containing initial concentrations of 1.5 and 10μmol Zn 1⁻¹. Depletion curves suggested that Zn uptake characteristics were similar at both levels of Zn in solution. The Imax for Zn uptake decreased from 550 to 400 pmol m⁻² root surface s⁻¹ between 16 and 22 d of growth while Km decreased from 2.2 to 1.5 μmol Zn²⁺ 1⁻¹. Cadmium uptake parameters were measured by controlling Cd²⁺ activities in nutrient solution betwen 6.3 to 164 nmol l⁻¹ by continuous circulation of nutrient solution through a mixed-resin system. Imax for Cd uptake was 400 pmol m⁻² root surface s⁻¹ at 15 and 22 d of growth. The magnitude of Km increased from 30 to 100 nmol Cd²⁺ 1⁻¹ during this time period. The Km value suggests that corn is efficient for Cd uptake. The results of these uptake studies are consistent with the observed uptake of Zn and Cd by corn seedlings in soils.     

Effects of Zn-complexes on zinc uptake by wheat (Triticum aestivum) roots: a comprehensive consideration of physical, chemical and biological processes on biouptake

Commonly used equilibrium models for metal biouptake, such as the Free Ion Activity Model (FIAM) and the Biotic Ligand Model (BLM), are limited to the cases in which mass diffusive transport is not the flux-determining step. In analyses of metal biouptake from a complexing medium, all the physical (diffusion), chemical (dissociation kinetics of metal complexes), and biological (transport and internalization) processes have to be taken into account. A short-term zinc uptake by wheat (Triticum aestivum) roots from culture solutions in the absence or presence of synthetic ligands (NTA, nitrilotriacetic acid, and EDTA, ethylenediaminetetraacetate) was studied. At the same free Zn²⁺ concentration $\left( {\left\{ {{\text{Zn}}^{{\text{2 + }}} } \right\} = 1.5 \times 10^{ - 8} {\text{M}}} \right)$ , the uptake of Zn was significantly enhanced in the presence of ligands and was larger when Zn complexes have a quicker dissociation rate. The diffusional fluxes in the same culture solution were determined with the differential pulse anodic stripping voltammetry (DPASV) method, and the diffusive gels in thin film (DGT) technique. The contribution from Zn complexes to root Zn uptake was in better agreement with the degree of Zn complex labilities measured with DPASV than with DGT. The diffusion of free Zn²⁺ ion to the root surface is a rate-controlling step for Zinc biouptake when the free Zn²⁺ concentration is low. Based on the comprehensive consideration of the diffusion and dissociation processes of Zn²⁺ ion and Zn complexes and the existence of high- and low-affinity uptake systems in the root surface, a two-pathway Zn uptake model was developed to predict the resulting Zn uptake fluxes into roots in the overall range of exposure.     

The effect of zinc and magnesium on calcium uptake into the rat duodenum slices

Summary The experiments were carried out on 80 male Wistar rats, divided into four groups as follows: group 1, treated orally with ZnCl₂ at a dose of 10 mg Zn²⁺/kg for 14 days; group 2, control; group 3, MgCl₂-treated at a dose of 5 mg Mg²⁺/kg; group 4, treated with ZnCl₂ plus MgCl₂ in the same manner as groups 1 and 3. The influx of calcium into the rat duodenum slices was investigated in vitro by the method of Papworth and Patrick. Over a range of calcium concentrations (0–10 mM) the influx of this element was defined as a sum of a saturable term (active transport) and a linear term dependent on concentration (passive transport). In the zinc-treated rats only the saturable term was affected. The study of this term by Lineweaver-Burk plots showed a decrease of the half-saturation constant,K _t, while the maximal value,J _m, remained unchanged. Moreover, magnesium was shown to interact with zinc at gut level because simultaneous oral administration of Mg²⁺ and Zn²⁺ to rats protected them against the inhibition of calcium uptake observed when Zn²⁺ was given alone.     

Kinetic properties of a micronutrient transporter from<Emphasis Type="Italic"> Pisum sativum</Emphasis> indicate a primary function in Fe uptake from the soil

Fe uptake in dicotyledonous plants is mediated by a root plasma membrane-bound ferric reductase that reduces extracellular Fe(III)-chelates, releasing Fe²⁺ ions, which are then absorbed via a metal ion transporter. We previously showed that Fe deficiency induces an increased capacity to absorb Fe and other micronutrient and heavy metals such as Zn²⁺ and Cd²⁺ into pea (Pisum sativum L.) roots [Cohen et al. (1998) Plant Physiol 116:1063–1072). To investigate the molecular basis for this phenomenon, an Fe-regulated transporter that is a homologue of the Arabidopsis IRT1 micronutrient transporter was isolated from pea seedlings. This cDNA clone, designated RIT1 for root iron transporter, encodes a 348 amino acid polypeptide with eight putative membrane-spanning domains that is induced under Fe deficiency and can functionally complement yeast mutants defective in high- and low-affinity Fe transport. Chelate buffer techniques were used to control Fe²⁺ in the uptake solution at nanomolar activities representative of those found in the rhizosphere, and radiotracer methodologies were employed to show that RIT1 is a very high-affinity ⁵⁹Fe²⁺ uptake system (K _m =54–93 nM). Additionally, radiotracer (⁶⁵Zn, ¹⁰⁹Cd) flux techniques were used to show that RIT can also mediate a lower affinity Zn and Cd influx (K _m of 4 and 100 M, for Zn²⁺ and Cd²⁺, respectively). These findings suggest that, in typical agricultural soils, RIT1 functions primarily as a high-affinity Fe²⁺ transporter that mediates root Fe acquisition. This is consistent with recent findings with Arabidopsis IRT1 knockout mutants that strongly suggest that this transporter plays a key role in root Fe uptake and nutrition. However, the ability of RIT1 to facilitate Zn and Cd uptake when these metals are present at elevated concentrations suggests that RIT1 may be one pathway for the entry of toxic metals into the food chain. Furthermore, the finding that plant Fe deficiency status may promote heavy metal uptake via increased expression of this transporter could have implications both for human nutrition and also for phytoremediation, the use of terrestrial plants to sequester toxic metals from contaminated soil.     

Solid phase speciation of Zn and Cd in zinc smelter effluent-irrigated soils

Solubility of metal in contaminated soils is a key factor which controls the phytoavailability and toxic effects of metals on soil environment. The chemical equilibria of metal ions between soil solution and solid phases govern the solubility of metals in soil. Hence, an attempt was made to identify the probable solid phases (minerals), which govern the solubility of Zn²⁺ and Cd²⁺ in zinc smelter effluent-irrigated soils. Estimation of free ion activities of Zn²⁺ (pZn²⁺) and Cd²⁺ (pCd²⁺) by Baker soil test indicated that metal ion activities were higher in smelter effluent-irrigated soils as compared to that in tubewell water-irrigated soils. Identification of solid phases further reveals that free ion activity of Zn²⁺ and Cd²⁺ in soil highly contaminated with Zn and Cd due to long-term irrigation with zinc smelter effluent is limited by the solubility of willemite (Zn₂SiO₄) in equilibrium with quartz and octavite (CdCO₃), respectively. However, in case of tubewell water-irrigated soil, franklinite (ZnFe₂O₄) in equilibrium with soil-Fe and exchangeable Cd are likely to govern the activity of Zn²⁺ and Cd²⁺ in soil solution, respectively. Formation of highly soluble minerals namely, willemite and octavite indicates the potential ecological risk of Zn and Cd, respectively in smelter effluent irrigated soil.     

Effect of clay,organic matter and CaCO3 content on zinc adsorption by soils

Summary Zinc adsorption was studied in suspensions of six soils of different physicochemical characteristics in dilute ZnSO₄ solutions. At low concentrations, Zn²⁺ adsorption was described by the Langmuir adsorption equation. The calculated Langmuir adsorption maxima were related positively to clay and carbonate content and negatively with organic matter content of soils. Multiple regression analysis revealed that zinc adsorption maxima can be predicted with good precision from information in soil survey reports. When the added Zn²⁺ exceeded the adsorption maximum, the solid phase of zinc controlling its concentration in solution was either zinc hydroxide or carbonate so long as soil carbonates were present. The values of zinc potential also indicated that soils retain Zn²⁺ more strongly than Zn(OH)₂ or carbonate. Postgraduate student Professor of Soils. Professor of Soils.     

Zinc uptake across the apical membrane of freshwater rainbow trout intestine is mediated by high affinity, low affinity, and histidine-facilitated pathways

Zinc is both a vital nutrient and an important toxicant to aquatic biota. In order to understand the interplay between nutrition and toxicity, it will be important to determine the mechanisms and the factors that regulate zinc uptake. The mechanism of apical intestinal Zn(II) uptake in freshwater rainbow trout and its potential modification by the complexing amino acid histidine was investigated using brush-border membrane vesicles (BBMVs). Following characterisation of the BBMV preparation, zinc uptake in the absence of histidine was both time- and concentration-dependent and consisted of two components. A saturable phase of uptake was described by an affinity constant of 57±17 μM and a transport capacity of 1867±296 nmol mg membrane protein⁻¹ min⁻¹. At higher zinc levels (>500 μM) a linear, diffusive component of uptake was evident. Zinc transport was also temperature-dependent, with Q₁₀ values suggesting zinc uptake was a carrier-mediated process. Zinc uptake by vesicles in the presence of histidine was correlated to a mono-histidine species (Zn(His)⁺) at all Zn(II) concentrations examined.     

Effects of interaction between65Zn,cadmium, and copper in rats

Distribution and retention of zinc in the presence of cadmium and copper was studied in rats exposed repeatedly to these metals. The experiment was performed on white rats of the Wistar strain. The animals were divided into four groups/five rats each: 1)⁶⁵ZnCl₂; 2)⁶⁵ZnCl₂+CdCl₂; 3)⁶⁵ZnCl₂+CuCl₂; and 4) control group. Rats were administered sc every other day for two weeks:⁶⁵ZnCl₂−5 mg Zn/kg; CdCl₂−0,3 Cd/kg; and CuCl₂−2 mg Cu/kg. The zinc content was measured in rat tissues by γ-counting. Effect of Cd and Cu on subcellular distribution of zinc in the kidney and liver and on the level of metallothionein were also examined. Whole body retention of zinc under the influence of cadmium was lower than that observed in animals treated with zinc alone. However, copper increased twofold the whole body retention of zinc. Cadmium elevated the accumulation of zinc only in the kidneys nuclear fraction and liver soluble fraction. In the kidneys and liver, copper elevated the accumulation of zinc, in the nuclear, mitochondrial, and soluble fractions. The level of metallothionein-like proteins (MT) in the kidneys after a combined supply of zinc and copper was significantly increased with respect to the group of animals treated with zinc alone. These results indicated complex interactions between cadmium, copper, and zinc that can affect the metabolism of each of the metals.     

Identification and characterization of zinc-starvation-induced ZIP transporters from barley roots

Zinc (Zn) is an essential element for plants but limited information is currently available on the molecular basis for Zn²⁺ transport in crop species. To expand the knowledge on Zn²⁺ transport in barley (Hordeum vulgare L.), a cDNA library prepared from barley roots was expressed in the yeast (Saccharomyces cerevisiae) mutant strain Δzrt1/Δzrt2, defective in Zn²⁺ uptake. This strategy resulted in isolation and identification of three new Zn²⁺ transporters from barley. All of the predicted proteins have a high similarity to the ZIP protein family, and are designated HvZIP3, HvZIP5 and HvZIP8, respectively. Complementation studies in Δzrt1/Δzrt2 showed restored growth of the yeast cells transformed with the different HvZIPs, although with different efficiency. Transformation into Fe²⁺ and Mn²⁺ uptake defective yeast mutants showed that the HvZIPs were unable to restore the growth on Fe²⁺ and Mn²⁺ limited media, respectively, indicating a specific role in Zn²⁺ transport. In intact barley roots, HvZIP8 was constitutively expressed whereas HvZIP3 and HvZIP5 were mainly expressed in ?Zn plants. These results suggest that HvZIP3, HvZIP5 and HvZIP8 are Zn²⁺ transporters involved in Zn²⁺ homeostasis in barley roots. The new transporters may facilitate breeding of barley genotypes with improved Zn efficiency and Zn content.     

Free zinc concentration in bovine milk measured by analytical affinity chromatography with immobilized metallothionein

A new analytical affinity chromatography method was developed for measuring the free [Zn²⁺] concentration in bovine milk. The column was generated by immobilizing avidin and attaching biotinylated metallothionein (MT) on controlled-pore glass beads. Zinc bound to the MT column at physiological free [Zn²⁺] concentration and was dissociated again in an elution buffer of pH 2. The distributions of extrinsically added⁶⁵Zn and native zinc in different fractions of milk were virtually identical, validating the use of extrinsic labeling in studies of the free [Zn²⁺] concentration in milk. Extrinsically labeled whey fractions were mixed with standard solutions whose free [Zn²⁺] concentrations were calculated by computer model.⁶⁵Zn retained by the column provided an indication of free [Zn²⁺] concentration in the mixture, and by interpolation, in the original milk. The free [Zn²⁺] concentration measured by the affinity chromatography method in the milk of a group of six cows was 90.4±29.7 pM. This value is similar to estimates of free [Zn²⁺] concentrations in other biological fluids by entirely different methods. Measurement of free [Zn²⁺] may be helpful in understanding the physiology and biochemistry of zinc metabolism.     

Zinc induces DNA damage in tobacco roots

We applied the alkaline version of the single-cell gel electrophoresis (comet assay) to seedlings of heterozygous tobacco (Nicotiana tabacum L. var. xanthi) treated with zinc acetate dihydrate (20 to 80 mM Zn²⁺ for 2 h or 2 to 12 mM Zn²⁺ for 24 h). A dose dependent increase in DNA damage expressed by the tail moment values were observed in nuclei isolated from the roots after 2 and 24 h Zn²⁺ treatments. In contrast, Zn²⁺ did not induce significant DNA damage to leaf nuclei, with the exception of 10 or 12 mM Zn²⁺ for 24 h. Somatic mutations, identified as dark green, yellow, and dark green/yellow double sectors on the pale green tobacco leaves were not detected after any Zn²⁺ treatments. The accumulation of Zn in roots and shoots was determined by inductively coupled plasma optical emission spectrometry and the Zn content in roots was about three times higher than in shoots.     

细菌锌离子调控体系与感染北大核心CSCD

锌(Zn)是生命体不可或缺的微量元素,对细菌和宿主同等重要。细菌体内锌离子稳态的维持依赖锌离子转运和调控体系。宿主通过限制锌离子或高锌离子中毒来控制细菌感染。为了在宿主体内生存,细菌必须表达高亲和力的锌离子转运系统,如ZnuABC,以获取足够的锌离子。由于锌与细菌大量的代谢和毒性通路密切相关,在细菌建立感染的过程中尤为重要,因此通过抑制锌离子转运系统来影响锌离子的稳态,将成为一个非常有发展前途的新型抗菌策略。     

Characteristics of Cd uptake, translocation and accumulation in a novel Cd-accumulating tree, star fruit (Averrhoa carambola L., Oxalidaceae)

Cadmium (Cd) accumulation by terrestrial higher plants is an intriguing phenomenon that may be exploited for phytoextraction of Cd-contaminated soils. Characterizing the physiological processes responsible for elevated concentrations of Cd in shoots is a first step towards a comprehensive understanding of the mechanisms underlying Cd accumulation in plants and may eventually improve the efficiency of phytoextraction. Woody species that can accumulate Cd have been recently recommended as good candidates for phytoextraction of Cd-contaminated soils. However, little is known about the mechanisms of Cd accumulation by woody species. In an attempt to understand the physiological processes contributing to Cd accumulation in woody species, Cd uptake and translocation by a novel tropical Cd-accumulating tree, star fruit (Averrhoa carambola) were characterized and compared with those of a non-Cd-accumulating tree (Clausena lansium). Our results showed that A. carambola had higher Cd uptake and root-to-shoot translocation efficiencies than C. lansium, which might account for its greater Cd-accumulating capacity. Furthermore, Cd accumulation by A. carambola was not significantly affected by zinc (Zn), whereas Zn accumulation was greatly lowered by Cd. This phenomenon could not be fully explained by a simple competition between Cd²⁺ and Zn²⁺, implying the existence of a transport system with a preference for Cd over Zn. Collectively, our results indicate that A. carambola has noteworthy physiological traits associated with accumulation of Cd to high levels.     

Zinc transport by respiratory epithelial cells and interaction with iron homeostasis

Despite recurrent exposure to zinc through inhalation of ambient air pollution particles, relatively little information is known about the homeostasis of this metal in respiratory epithelial cells. We describe zinc uptake and release by respiratory epithelial cells and test the postulate that Zn²⁺ transport interacts with iron homeostasis in these same cells. Zn²⁺ uptake after 4 and 8 h of exposure to zinc sulfate was concentration- and time-dependent. A majority of Zn²⁺ release occurred in the 4 h immediately following cell exposure to ZnSO₄. Regarding metal importers, mRNA for Zip1 and Zip2 showed no change after respiratory epithelial cell exposure to zinc while mRNA for divalent metal transporter (DMT)1 increased. Western blot assay for DMT1 protein supported an elevated expression of this transport protein following zinc exposure. RT-PCR confirmed mRNA for the metal exporters ZnT1 and ZnT4 with the former increasing after ZnSO₄. Cell concentrations of ferritin increased with zinc exposure while oxidative stress, measured as lipid peroxides, was decreased supporting an anti-oxidant function for Zn²⁺. Increased DMT1 expression, following pre-incubations of respiratory epithelial cells with TNF-α, IFN-γ, and endotoxin, was associated with significantly decreased intracellular zinc transport. Finally, incubations of respiratory epithelial cells with both zinc sulfate and ferric ammonium citrate resulted in elevated intracellular concentrations of both metals. We conclude that exposure to zinc increases iron uptake by respiratory epithelial cells. Elevations in cell iron can possibly affect an increased expression of DMT1 and ferritin which function to diminish oxidative stress. Comparable to other metal exposures, changes in iron homeostasis may contribute to the biological effects of zinc in specific cells and tissues.     

Cadmium and Zinc are differentially distributed in Populus tremula x P. alba exposed to metal excess

Abstract

Poplar plants were exposed during 61 days to a soil added with heavy metals so as to contain 300 mg Zn²⁺.kg^?1 soil dry weight (SDW) (Zinc) or 50 mg Cd²⁺.kg^?1 SDW (Cadmium). The Cd treatment induced a delayed growth of poplar, whereas Zn induced no change in physiological parameters. Both treatments resulted in a significant metal accumulation in plants. Zn²⁺ and Cd²⁺ exhibited contrasting distribution within tissues, indicating dissimilar handling by the plant. The main difference was the efficient compartmentalisation of Zn²⁺ in specific organ parts: old leaves and bark, while Cd²⁺ did not exhibit such a compartmentalisation. Results were also compared with a previous work where plants were exposed to 360 mg Cd²⁺.kg^?1 SDW.