MT-like Proteins Research Articles

“Nanosize effect” in the metal-handling strategy of the bivalve Scrobicularia plana exposed to CuO nanoparticles and copper ions in whole-sediment toxicity tests

To date, the occurrence, fate and toxicity of metal-based NPs in the environment is under investigated. Their unique physicochemical, biological and optical properties, responsible for their advantageous application, make them intrinsically different from their bulk counterpart, raising the issue of their potential toxic specificity or “nanosize effect”. The aim of this study was to investigate copper bioaccumulation, subcellular distribution and toxic effect in the marine benthic species Scrobicularia plana exposed to two forms of sediment-associated copper, as nanoparticles (CuO NPs) and as soluble ions (CuCl2). Results showed that the exposure to different copper forms activated specific organism's metal handling strategies. Clams bioaccumulated soluble copper at higher concentrations than those exposed to sediment spiked with CuO NPs. Moreover, CuO NPs exposure elicited a stronger detoxification response mediated by a prompt mobilization of CuO NPs to metal-containing granules as well as a delayed induction of MT-like proteins, which conversely, sequestered soluble copper since the beginning of the exposure at levels significantly different from the control. Eventually, exposure to high concentrations of either copper form led to the same acute toxic effect (100% mortality) but the outcome was delayed in bivalves exposed to CuO NPs suggesting that the mechanisms underlying toxicity were copper form-specific. Indeed, while most of soluble copper was associated to the mitochondrial fraction suggesting an impairment of the ATP synthesis capacity at mitochondrial level, CuO NPs toxicity was most likely caused by the oxidative stress mediated by their bioaccumulation in the enzymatic and mitochondrial metabolically available fractions.

MT-like proteins: Potential bio-indicators of Chlorella vulgaris for zinc contamination in water environment

Chlorella vulgaris has been usually used to monitor the toxicity of Zn in water environment, but the biochemical responses of the algae to Zn2+ at different levels remain unknown to date. In the present study, the growth inhibition, the antioxidant enzymes, the subcellular Zn and the induced Zn-metallothionein-like (Zn-MT-like) proteins in C. vulgaris exposed to 0, 5, 10, 20, 50 and 100μmoll−1 of Zn2+ were investigated. Results showed that the growth of C. vulgaris was significantly inhibited (p<0.05) at Zn2+ level above 5μmoll−1. Compared with the control group, the activities of peroxidase (GSH-Px), superoxide dismutase (SOD) and catalase mostly increased with the rises of Zn2+ concentrations ranging from 5 to 100μmoll−1, except for GSH-Px with a lower value in the 100μmoll−1 group compared with that of the 50μmoll−1 group, and SOD with no significant difference at the 5, 10 and 100μmoll−1 groups compared with that of the control group. Contrarily, the activities of guaiacol peroxidase significantly decreased (p<0.05) at Zn2+ concentrations from 5 to 100μmoll−1 compared with that of the control group. After 72h exposure, Zn in the algal cells was observed to mainly distribute in the form of heat stable fractions, in which Zn-binding metallothionein-like (MT-like) proteins were largely biosynthesized. In addition, the amounts of Zn-MT-like proteins induced in the algae significantly increased (p<0.05) with the rises of Zn2+ concentrations at the assay levels. The results indicated that the activities of antioxidant enzymes and the induction of Zn-MT-like proteins in C. vulgaris may play important roles in dealing with the toxicity of Zn2+ to the algal cells, and the induction of Zn-MT-like proteins in C. vulgaris can be used as a potential bio-indicator to monitor the contamination of Zn2+ in water environment.

Expression analysis of new Metallothionein2-like protein under mercury stress in tomato seedling

Plants including tomato produce several kinds of chelator proteins such as metallothioneins (MTs) for protection against Hg 2+ toxicity. However, the mechanism of protection from Hg 2+ is not perfectly clear. Hg 2+ content subsequently was plateaued from days 1 to 7. Cell death and DNA digestion were not observed in the primary root in the presence of Hg 2+ over the 7 days. The predicted protein sequences of 5 tomato type 2 MT-like (MT2-like) proteins were compared. The coding sequences of accession number Z68185 had no Cys-Cys motif in the N-terminal. However, the Z68185 cDNA genetic recombinant showed high resistance to Hg 2+ in bacteria. In tomato, the expression was observed in the roots, but not in the leaves or stems. mRNA of the MT2-like protein was measured in tomato seedlings exposed to 1 μM Hg 2+ . The expression level did not increase until day 3, but increased expression was observed after day 5. These results suggest that new Metallothionein2-like protein express in root specific and it may trap mercury. Our results indicate that functional identification of an MT2-like protein will be useful for molecular breeding designed to improve plant tolerance to Hg 2+ .

Dehydroascorbate reductase and monodehydroascorbate reductase activities of two metallothionein-like proteins from sweet potato (Ipomoea batatas [L.] Lam. 'Tainong 57') storage roots.

BackgroundMetallothionein (MT) is a group of proteins with low molecular masses and high cysteine contents, and it is classified into different types, which generally contains two domains with typical amino acid sequences.ResultsIn this report, two full-length cDNAs (MT-1 and MT-II) encoding MT-like proteins were isolated from the roots of sweet potato (Ipomoea batatas [L.] Lam. ‘Tainong 57’). Their open reading frames contained 642 and 519 nucleotides (66 and 81 amino acids) for MT-1 and MT-II, respectively, and exhibited a relatively low amino acid sequence similarity. On the basis of the amino acid sequence similarity and conserved residues, it is suggested that MT-I is a member of the plant MT Type-I family, and MT-II is a member of the plant MT Type-II family. The corresponding mRNA levels of MT-1 and MT-II were the highest found in the storage roots. Recombinant MT-1 and MT-II protein overproduced in E. coli (M15) was purified by Ni2+-chelated affinity chromatography. MT-1 and MT-II reduced dehydroascorbate (DHA) in the presence of glutathione (GSH) to regenerate L-ascorbic acid (AsA). However, without GSH, MT-1 and MT-II has very low DHA reductase activity. And AsA was oxidized by AsA oxidase to generate monodehydroascorbate (MDA) free radical. MDA was also reduced by MT-1 and MT-II to AsA in the presence of NADH mimicking the MDA reductase catalyzed reaction.ConclusionsThese data suggest that MT-1 and MT-II have both DHA reductase and MDA reductase activities. MT-1 and MT-II are apparently the first reported plant MTs exhibiting both DHA and MDA activities in vitro.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-54-7) contains supplementary material, which is available to authorized users.

CDNA sequence encoding metallothionein protein from Aegiceras corniculatum and its gene expression induced by Pb2+ and Cd2+ stresses

Constructing various green wetland examples for mangrove wetland systems is a useful way to use natural power to remediate the polluted wetlands at intertidal zones. Metallothioneins (MT) are involved in heavy metal tolerance, homeostasis, and detoxification of intracellular metal ions in plants. In order to understand the mechanism of heavy metal uptake in Aegiceras corniculatum, we isolated its metallothionein gene and studied the MT gene expression in response to heavy metals contamination. Here, we report the isolation and characterization of MT2 genes from young stem tissues of A. corniculatum growing in the cadmium (Cd) and lead (Pb) polluted wetlands of Quanzhou Bay, southeast of China. The obtained cDNA sequence of MT is 512 bp in length, and it has an open reading frame encoding 79 amino acid residues with a molecular weight of 7.92 kDa and the theoretical isoelectric point of 4.55. The amino acids include 14 cysteine residues and 14 glycine residues. It is a non-transmembrane hydrophilic protein. Sequence and homology analysis showed the MT protein sequence shared more than 60% homology with other plant type 2 MT-like protein genes. The results suggested that the expression level of MT gene of A. corniculatum young stems induced by a certain range concentration of Cd(2+) and Pb(2+) stresses (0.2 mmol L(-1) Pb(2+), 1 mmol L(-1) Pb(2+), 0.2 mmol L(-1) Pb(2+), and 40 μmmol L(-1) Cd(2+); 1 mmol L(-1) Pb(2+) and 40 μmol L(-1) Cd(2+)) compared with control might show an adaptive protection. The expression levels of MT gene at 20 h stress treatment were higher than those at 480 h stress treatment. The expression levels of MT gene with 0.2 mmol L(-1) Pb(2+) stress treatment were higher than those with 0.2 mmol L(-1) Pb(2+) and 40 μmol L(-1) Cd(2+) stress treatment, and the MT gene expression levels with 1 mmol L(-1) Pb(2+) treatment were higher than those with 1 mmol L(-1) Pb(2+) and 40 μmol L(-1) Cd(2+) treatment. There exists an antagonistic action between Pb(2+) and Cd(2+) in the MT metabolization of A. corniculatum.

Effect of gamma irradiation on metallothionein protein expression in Plantago ovata Forsk

Purpose: The effect of gamma rays on metallothionein (MT) expression was studied using the medicinal plant Plantago ovata as the test system.Materials and methods: Western blotting and Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) were used for this purpose.Results: Western blot analysis showed significant induction of metallothionein protein following gamma exposure and that induction was highest at 20 Gy gamma dose. At higher gamma doses (100 Gy) MT expression level declined due to degeneration of cells. MALDI-TOF MS analysis indicated the presence of low molecular weight (7–8 kD) MT molecules following the lower radiation doses.Conclusion: It was concluded from the MALDI-TOF MS result that low gamma exposure leads to expression of MT-like protein. At high doses of gamma ray, MT homologues or MT-like protein were not identified, possibly because they might have precipitated due to uncontrolled cross-linking and non-specific aggregation.

A novel metallothionein gene from a mangrove plant Kandelia candel

A new metallothionein (MT) gene was cloned from Kandelia candel, a mangrove plant with constitutional tolerance to heavy metals, by rapid amplification of cDNA ends and named KMT, which is composed of two exons and one intron. The full length of KMT cDNA was 728 bp including 121 bp 5' noncoding domain, 240 bp open reading frame and 384 bp 3' termination. The coding region of KMT represented a putative 79 amino acid protein with a molecular weight of 7.75 kDa. At each of the amino- and carboxy-terminal of the putative protein, cysteine residues were arranged in Cys-Cys, Cys-X-Cys and Cys-X-X-Cys, indicating that the putative protein was a novel type 2 MT. Sequence and homology analysis showed the KMT protein sequence shared more than 60 % homology with other plant type 2 MT-like protein genes. At amino acid level, the KMT was shown homology with the MT of Quercus suber (83 %), of Ricinus communis (81 %) and of Arabidopsis thaliana (64 %). Function studies using protease-deficient Escherichia coli strain BL21 Star ™(DE3) confirmed the functional nature of this KMT gene in sequestering both essential (Zn) and non-essential metals (Cd and Hg) and the E. coli BL21 with KMT can live in 1,000 μmol/L Zn, 120 μmol/L Hg, and 2,000 μmol/L Cd. The information could provide more details of the causative molecular and biochemical mechanisms (including heavy metal sequestration) of the KMT in K. candel or a scientific basis for marine heavy-metal environment remediation with K. candel. This study also provides a great significance of protecting mangrove species and mangrove ecosystem.

Variation of metallothionein-like protein and metal concentrations during the reproductive cycle of the cockle Cerastoderma glaucum from an uncontaminated site: A 1-year study in the Gulf of Gabès area (Tunisia)

Natural variation of metallothionein-like protein (MTLP) concentrations in the cockle Cerastoderma glaucum were analysed over a 1-year period in specimens collected from a relatively uncontaminated site in the Gulf of Gabès (Tunisia). Sampling was carried out from June 2004 to June 2005. At each sampling time, water temperature and salinity were measured. Levels of zinc, cadmium and copper were measured in the whole soft tissues of the cockle C. glaucum. MT-like protein and subcellular metal partitioning were measured in the digestive gland. A histological study was conducted simultaneously to follow the development of the gonad in relation to the reproductive cycle of this bivalve. Results showed a significant fluctuation in MTLP concentrations throughout the whole year, with a maximum value measured in summer and in the late winter. The relationship between MTLP and metal concentrations, abiotic (temperature and salinity) and biotic (mass of target tissues) and also maturity index (MI) factors were examined. Metal levels in the tissues are likely to change during the season, reflecting variability in metabolism and/or a change in tissue weight. However, possible seasonal changes in trace metal concentration are unlikely to entirely explain the observed pattern in the MTLP levels. The physiological changes caused by gonad development and food abundance (change in tissue mass) contribute to a significant variability in MTLP levels in the cockle C. glaucum and can interfere with the estimation of level changes induced by anthropogenic sources.

The dynamics of protein and metal metabolism in acclimated and Cd-exposed freshwater crabs ( Potamonautes warreni)

Climatic and man-made impacts induced dynamic molecular responses in the South African freshwater crab, Potamonautes warreni. Adult crabs exhibited MT-like protein, binding Cd (0.02 μmol g −1 wet mass±0.02), Cu (0.326 μmol g −1 wet mass±0.15), and Zn (0.534 μmol g −1 wet mass±0.20). The native protein binding Cd, Cu, and Zn showed a respective molecular mass ( M) of 9.10 kDa±1.74, 8.95 kDa±1.66, and 9.32 kDa±0.93. With exposure to 0.2 mg Cd 2+ l −1 for up to 21 days in 50% of these crabs approximately 90% of Cd was bound to the MT-like protein component (8.54 kDa±1.64), coinciding with a Zn-bound MT-like component (8.2 kDa±1.54). Less than 10% were bound in the high M protein component, suggesting a protective function of the protein. In the remaining crabs metals were bound to protein (6.8 kDa) with a predominant Cu-binding component.

Growth-inhibitory and metal-binding proteins in Chlorella vulgaris exposed to cadmium or zinc

Phytochelatins, with the general structure of (γ-Glu–Cys) n–Gly ( n = 2–11), are usually recognized as being strongly induced by metals in microalgae and play an important role in the detoxification of heavy metals in environment. However, there have been few studies on metallothionein (MT) synthesis in Chlorella vulgaris ( C. vulgaris) exposed to heavy metals. The present study describes the growth inhibition of C. vulgaris exposed to different concentrations of cadmium and zinc, and the induction of metal-binding MT-like proteins in the cells. The amounts of metal-binding proteins, induced in the alga exposed to different concentrations of Cd and Zn, were analyzed with a size-exclusion HPLC coupled to ICP–MS. After being purified with a gel filtration column (Sephadex G-75, 3.5 cm × 80 cm) and a desalting column (G-25, 1.5 cm × 30 cm), the isoforms and sub-isoforms of Zn-binding protein were characterized by a reverse phase-HPLC coupled to electrospray ionization and a triple quadrupole mass spectrometer (HPLC–ESI–MS/MS). In addition, the ultraviolet spectra of purified Zn-binding proteins were analyzed in media with different pH values. The results showed that the significant inhibitory effects (at p < 0.05) on the cell growth were observed when excessive metals such as 80 μmol l −1 of Cd, and 60 and 80 μmol l −1 of Zn were added. The Cd/Zn-binding proteins induced in C. vulgaris exposed to Cd and Zn were referred to as Cd/Zn-MT-like proteins in which the mean molecular mass of the apo-MT-like was 6152 Da. The induced Cd/Zn-MT-like proteins might be involved in the detoxification of heavy metals, such as cadmium and zinc, by the alga.

Assessment of sediment/water contamination by in vivo transplantation of the cockles Cerastoderma glaucum from a non contaminated to a contaminated area by cadmium

In this study the cockle Cerastoderma glaucum, a filter-feeding bivalve living in the upper layer of sediment was used to investigate the cadmium contamination at a heavily urbanised and industrial area, with a view to using them as an indicator of water/sediment contamination. To this end, cockles collected from indigenous population in a relatively uncontaminated site (Ras Ungha) were in vivo transplanted into sediment and water removed from cadmium contaminated site (El Hofra) for 45 days. The manipulative experiment was undertaken in order to examine the trace metal bioavailability in the contaminated area and to establish an analytical framework between the bioaccumulation of cadmium in the tissues and their biological effect in transplanted cockles. For this purpose, a range of sublethal stress biomarkers were selected on the basis of their potential to provide relevant information. Cadmium concentrations were determined in the sediment and in the soft tissue of the cockles from the two studied stations at time 0. Compared to the reference site, cadmium concentrations in the contaminated site were 53 higher in the sediment and 15 higher in the whole soft tissues. The variation of cadmium concentrations and biomarkers responses in transplanted cockles were determined as a function of exposure time. After 45 days' experience, cadmium concentrations increased by a factor of 5 compared with time 0. No significant change could be detected in controls. In the digestive gland of exposed cockles cadmium was mainly associated with the cytosolic fraction. The significant increase of cadmium concentration in the soluble fraction was followed by a significant increase in the concentration of the Sulphydryl-Containing Heat Stable Compounds (SCHSC) including metallothionein like proteins by approximately 86%. This is led to investigation into possible existence of an induction of MT-like proteins in relation to cadmium accumulated by exposed cockles. Transplanted cockles were also subjected to some stress effect consisting in significant inhibition of cholinesterase activity by 26.5% when compared with control cockles. Increased levels of malondialdehydes (MDA) following cadmium exposure have been also reported, suggesting that exposed cockles have been submitted to an oxidative stress probably due to the presence of high cadmium contamination in the sediment. Principal component analyses showed that cockles in vivo transplanted into cadmium contaminated sediment and water were standing out progressively from the control group as a function of exposure time. A clear separation of the transplanted cockles from their controls was observed after 45 days' experience. But, the transplanted cockles appeared not having yet reached the same characteristics as the resident cockles from the contaminated site.

The effect of in situ cadmium contamination on some biomarkers in Cerastoderma glaucum

The present study was designed to detect in situ effects of cadmium on marine organisms Cerastoderma glaucum from the gulf of Gabès (Tunisia). Six sampling stations were chosen: one site, relatively far from known local source of pollution, was considered as uncontaminated site and five sites clearly exposed to anthropogenic impact. Metallothionein like protein (MTLP) and sub-cellular metal partitioning were measured in cockles (C. glaucum) gills and digestive gland. Various biomarkers were also measured, including malondialdehyde (MDA) in the digestive gland and acetylcholinesterase activity (AChE) in the remainder. The health status of the cockles was assessed by using the condition index (CI). Significant differences between sites were noted for Cd concentrations, (CI) and also for the three studied biomarkers. Significant higher biomarkers response was measured in cockles from stations located in the northern part of the gulf, which are exposed directly to industrial and urban effluents, whereas the response of most biomarkers was minimal at the reference station. Positive and significant correlations were observed between MTLP and Cd concentrations in the digestive gland and in the gills. However, it must be noted that these correlations were more significant in the digestive gland, suggesting that compared to the gills, the digestive gland of C. glaucum is more suitable for monitoring metal pollution. The subcellular distribution of Cd showed that the soluble fraction was the major compartment for Cd storage, a pattern which is due to the role of MTLP in Cd detoxication. But at the most contaminated site (EH), cadmium in the digestive gland was preferentially accumulated in the insoluble fraction (P1) suggesting that the MTLP capacity in binding metals was not sufficient to avoid the binding of Cd to the insoluble fraction. Furthermore, the MTLP concentrations in the cockles from this site are lower than expected. So in highly polluted sites, MTLP in C. glaucum should not be used as a useful biomarker for metal pollution. The lipid peroxidation as presented by malondialdehyde levels, and MT-like protein concentrations increased in cockles exposed to cadmium contamination. We can, therefore, hypothesize that Cd could induce MTLP synthesis and MDA increase. While AChE had distinct and specific pattern showing that cadmium is not the only factor of the inhibition of cholinesterase activity. There are other polluting inputs engendering this inhibition.

The fine‐tuning of heavy metals in mycorrhizal fungi

The fine‐tuning of heavy metals in mycorrhizal fungi

Localization of metallothionein, heat shock protein (Hsp70), and superoxide dismutase expression inHemidiaptomus roubaui(Copepoda, Crustacea) exposed to cadmium and heat stress

Immunohistochemical methods were applied in the present study to investigate the expression of stress proteins such as metallothioneins (MT), which are metal-binding proteins, and heat shock proteins (Hsp70), as well as an antioxidant enzyme (superoxide dismutase, SOD), in the freshwater crustacean copepod Hemidiaptomus roubaui (Richard, 1888) exposed to cadmium or heat stress. The results show a tissue-specific distribution of MT-like protein after cadmium exposure in the brain and in the nerve cord. Cadmium stress did not provoke inducible Hsp70 or SOD expression. Unlike cadmium, heat stress induced the expression of Hsp70 and SOD in the shell glands, a structure involved in the reproductive function, and more particularly in the formation of the diapause egg envelope. MT expression is not induced in animals exposed to heat stress.

Metallothionein responses in the Asiatic clam (Corbicula fluminea) after exposure to trivalent arsenic

The main objective of this work was to evaluate arsenic effects on metallothionein (MT) induction by exposing a freshwater Asiatic clam (Corbicula fluminea) to different concentrations of this metalloid. The presence of MT-like proteins was detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis and compared with a standard rabbit MT. In addition, the polarographic response showed good correspondence between standard MT and MT-like curves from C. fluminea, allowing MT quantification. The results show that clams exposed to different concentrations of arsenic are able to induce significant levels of MTs. Although variability was found in MT induction, significant differences in MT levels were found after 28 days of exposure in all treatments in comparison with the controls, suggesting that exposure to arsenic induced MT-like proteins in C. fluminea.

Rapid isocratic HPLC quantification of metallothionein-like proteins as biomarkers for cadmium exposure in the earthworm Eisenia andrei

Metallothioneins (MTs) are regarded as sensitive biomarkers of cadmium (Cd) exposure in a number of organisms. An isocratic high-performance liquid chromatography (HPLC) method using the fluorophore ammonium-7-fluorobenz-2-oxa-1,3-diazole-4-sulfonate (SBD-F) and UV detection was developed for the quantification of MT-like proteins (MTLPs) in earthworm. This method was developed using a rabbit MT (MT-1) standard, and optimized concentrations of reagents including EDTA, SBD-F, and tris(2-carboxyethyl)phosphine (TCEP). The fluoro-tagged MT-1 (SBD-MT) and MTLP (SBD-MTLP) co-eluted at 7.2–7.3 min retention time on HPLC chromatograms. The optimized method was applied to quantify MTLPs in earthworms exposed to increasing concentrations of Cd (0, 2.7, 26.7, and 267.5 μg g −1 of wet artificial soil) for 1–4 weeks. The amounts of MTLPs increased significantly in a dose- and time-dependent manner except in controls and in earthworms exposed to the lowest concentration of Cd. Since earthworm MTLPs are temporal- and dose-responsive to Cd exposure, they can be used as biomarkers to assess the impact of Cd contamination in soils. The method appeared to be rapid, sensitive, and suitable for direct quantification of total earthworm MTs.

Isolation of putative type 2 metallothionein encoding sequences and spatial expression pattern in the seagrass Posidonia oceanica

Metallothioneins (MTs) are a group of proteins with low molecular mass and high cysteine content that bind to heavy metals and are thought to play a role in their metabolism and detoxification. Genes encoding MT-like proteins have been isolated in a number of plants. In this work we isolated nine MT-like sequences from copper- or cadmium-exposed plants of the seagrass Posidonia oceanica, a marine Angiosperm playing a major role in maintaining infralittoral ecosystems in the Mediterranean sea. These sequences, together with two other MT genes previously isolated from this species, show high similarities with genes encoding type 2 MTs. Neighbour-joining analysis, at both deduced protein and 3′-UTR sequence level, indicates that at least two subgroups occur within Posidonia type 2 MTs, showing, however, a strong sequence uniformity. Southern analysis of two type 2 MT-encoding sequences ( Pomt2b and Pomt2f) belonging to the two different subgroups showed distinct hybridisation patterns. For both type 2 MTs, we have determined, by in situ technique, the expression domain in Posidonia plants. The members of these two MT subgroups show differences in their histological expression, with Pomt2b associated with proliferative tissues whereas Pomt2f is associated with lignified or suberized cell wall.

The effects of temperature and metal exposures on the profiles of metallothionein-like proteins in Oreochromis niloticus

Freshwater fish Oreochromis niloticus were exposed individually to 1 mg/L concentrations of cadmium and zinc for 14 days at 20, 25 and 30° C. Heat-treated (80° C) liver tissue homogenates were run on a column packed with Sephadex G-75 to obtain eluats for determination of metallothionein-like proteins, sulfhydryl groups and metal concentrations. Elution profiles of the liver showed that there were three heat-resistant protein peaks detected at 254 and 280 nm in all samples. Approximate molecular weights of proteins obtained from the first, second and third peaks were 70,000, 43,000 and 6500 Da, respectively. Metallothionein-like proteins (6500) of control fish contained sulfhydryl groups and zinc, but not cadmium. Concentrations of zinc and cadmium in MT-like proteins increased in metal exposed fish and these increases were temperature dependent. However, zinc concentration in control fish decreased in relation to temperature increase. Data indicated that temperature plays significant role on metals bound on metallothioneins. This suggests that season of sampling should be taken into account when natural monitoring studies are carried out with metallothioneins.

Linking changes in subcellular cadmium distribution to growth and mortality rates in transplanted freshwater bivalves ( Pyganodon grandis)

Relationships between Cd accumulation and subcellular distribution, and growth and mortality rates were examined in the freshwater bivalve Pyganodon grandis in a transplant experiment. Organisms were transferred from a clean lacustrine site to four lakes situated along a Cd concentration gradient in the mining region of Rouyn-Noranda. The bivalves were maintained in open enclosures placed in the bottom sediments of the littoral zone of all five lakes for 400 days. At the end of the experiment, metallothionein (MT) was measured in the bivalve gills with a Hg-saturation assay and Cd partitioning among the various cytosolic protein pools was determined by size-exclusion chromatography. Marked differences were observed among the five sites: the range in calculated free-cadmium ion concentrations in water overlying the sediments was 35-fold whereas Cd concentrations in the gill cytosol of the transplanted bivalves varied three-fold. In the transplanted bivalves, the distribution of gill Cd among the various cytosolic complexes also varied significantly among sites. For bivalves transplanted to the three most contaminated sites, Cd concentrations in the high molecular weight pool (HMW > 25 kDa) were significantly higher than the baseline levels determined from bivalves caged at the reference site; a similar trend was seen for Cd concentrations in the metallothionein pool (Cd–MT). For bivalves transferred to two of the high contamination sites, proportionately less of the gill cytosolic Cd was sequestered (i.e. detoxified) by MT-like proteins. Reductions in survival were also observed at these two sites, and these elevated mortalities, in turn, were consistent with the absence of indigenous bivalve populations at these sites. This result is compatible with our recent work on P. grandis populations living in lakes of the Rouyn-Noranda area, in which we demonstrated that excessive accumulation of Cd in the HMW pool of the gill cytosol of the individual mollusks could be related to the impairment of population health status.

Modulatory Effect of Cadmium Exposure on Deltamethrin-Induced Oxidative Stress in Channa punctata Bloch

The modulatory effect of cadmium pretreatment (0.2 mg/kg b.w. i.p.) on deltamethrin-induced oxidative stress and alterations of antioxidants was studied in freshwater fish Channa punctata Bloch. Lipid peroxidation (LPO) was measured as one of the indicators of oxidative stress. Activities of glutathione peroxidase, glutathione reductase, and glutathione-S-transferase were also studied in liver, kidney, and gills. Levels of reduced glutathione (GSH) were measured in various tissues. Fish pretreated with cadmium and subsequently exposed to deltamethrin showed significantly reduced LPO values when compared with deltamethrin-exposed fish. Conversely, in the kidney, a potentiation response was observed. Deltamethrin exposure in fish resulted in significant alteration in activities of glutathione-dependent antioxidant enzymes. In the cadmium preexposed fish, which were subsequently exposed to deltamethrin, antioxidant enzymes showed a tendency toward normalization over deltamethrin-only exposed fish in liver and gills. GSH also showed a similar pattern in liver and gills but in kidney it remained elevated. Cadmium alone had no significant effect on various parameters at the concentration used in this study. When metallothionein (MT) induction was studied, only liver showed an MT-like protein band in sodium dodecylsulfate-polyacrylamide gel electrophoresis analysis. These results demonstrate a modulatory role of cadmium on the oxidative stress and other related parameters in liver and gills. These findings are important in the context of exposure to a mixture of pollutants in aquatic environment.