Colorimetric Sensor Array Based on Amino Acid-Modified Gold Nanoparticles for Toxic Metal Ion Detection in Water.

Several chromatographic and spectroscopic methods are available for the detection of toxic mercury (Hg2+) in water; however simple, rapid, inexpensive, and sensitive methods are still needed. In this chapter, we describe a facile, very sensitive, and rapid method for the colorimetric detection of Hg2+ in water with the detection limit of 2.9 nM. This simple procedure is based on the lysine-induced aggregation of citrate-capped gold nanoparticles (AuNPs) in the presence of Hg2+ ions.

Identification of Several Toxic Metal Ions Using a Colorimetric Sensor Array.

Water pollution by toxic metal ions is a worldwide environmental and health problem, and therefore monitoring of toxic metal ions in water resources is highly desired. In this chapter, we describe a simple colorimetric sensor array for simultaneous detection of multiple toxic heavy metal ions (Hg2+, Cd2+, Fe3+, Pb2+, Al3+, Cu2+, and Cr3+) in water. This assay is produced by using 11-mercaptoundecanoic acid (MUA)-capped gold nanoparticles (AuNPs) and five amino acids (lysine, cysteine, histidine, tyrosine, and arginine). The presence of amino acids can enhance or diminish the aggregation MUA-capped AuNPs with metal ions. The color change of the sensor array after aggregation in some of the channels creates unique response patterns for each metal ion.

The regulation of oxidative phosphorylation pathway on Vibrio alginolyticus adhesion under adversities.

Vibrio alginolyticus is one of the most important pathogens in mariculture and leading to heavy losses. After treatment with Cu2+ , Pb2+ , and low pH, the expression of oxidative phosphorylation pathway genes, including coxA, coxB, coxC, ccoN, ccoO, and ccoQ, was found commonly downregulated by RNA-seq as well as quantitative real-time PCR. RNAi significantly reduced the expression of coxA, coxB, coxC, ccoN, ccoO, and ccoQ in V. alginolyticus. Compared with the wild-type strain, the adhesion abilities of RNAi strains of V. alginolyticus were significantly impaired, as well as their cytochrome C oxidase activity. ccoQ appeared to be more important in the regulation of bacterial adhesion in these target genes, while ccoO was relatively weak in the regulation of the adhesion. Meanwhile, the changes of temperature, salinity, pH, and starvation affected coxA, coxB, coxC, ccoN, ccoO, and ccoQ expression remarkably. These findings indicated that: the oxidative phosphorylation pathway is a critical regulator of adhesion in V. alginolyticus; coxA, coxB, coxC, ccoN, ccoO, and ccoQ regulate the bacterial adhesion in response to environmental changes such as temperature, salinity, pH, and starvation.

Reactive cysteine residues in the oxidative dimerization and Cu2+ induced aggregation of human γD-crystallin: Implications for age-related cataract.

Cysteine (Cys) residues are major causes of crystallin disulfide formation and aggregation in aging and cataractous human lenses. We recently found that disulfide linkages are highly and partly conserved in ß- and γ-crystallins, respectively, in human age-related nuclear cataract and glutathione depleted LEGSKO mouse lenses, and could be mimicked by in vitro oxidation. Here we determined which Cys residues are involved in disulfide-mediated crosslinking of recombinant human γD-crystallin (hγD). In vitro diamide oxidation revealed dimer formation by SDS-PAGE and LC-MS analysis with Cys 111-111 and C111-C19 as intermolecular disulfides and Cys 111-109 as intramolecular sites. Mutation of Cys111 to alanine completely abolished dimerization. Addition of αB-crystallin was unable to protect Cys 111 from dimerization. However, Cu2+-induced hγD-crystallin aggregation was suppressed up to 50% and 80% by mutants C109A and C111A, respectively, as well as by total glutathionylation. In contrast to our recently published results using ICAT-labeling method, manual mining of the same database confirmed the specific involvement of Cys111 in disulfides with no free Cys111 detectable in γD-crystallin from old and cataractous human lenses. Surface accessibility studies show that Cys111 in hγD is the most exposed Cys residue (29%), explaining thereby its high propensity toward oxidation and polymerization in the aging lens.

Molecular basis of Cd+2 stress response in Candida tropicalis.

This study examines the bioremediation potential and cadmium-induced cellular response on a molecular level in Candida tropicalis 3Aer. Spectroscopic analysis clearly illustrated the involvement of yeast cell wall components in biosorption. Cadmium bioaccumulation was confirmed by TEM, SEM, and EDX examination. TEM images revealed extracellular as well as cytoplasmic and vacuolar cadmium nanoparticle formation, further validated by presence of ycf1 gene and increased biosynthesis of GSH under cadmium stress. Fourteen proteins exhibited differential expression and during cellular redox homeostasis are found to involve in nitrogen metabolism, nucleotide biosynthesis, and carbohydrate catabolism. Interestingly, C. tropicalis 3Aer is equipped with nitrile hydratase enzyme, rarely been reported in yeast. It has the potential to remove nitriles from the environment. The Cd+2 toxicity not only caused growth stasis but also upregulated the cysteine biosynthesis, protein folding and cytoplasmic detoxification response elements. The present study suggests that C. tropicalis 3Aer is a potential candidate for bioremediating environmental pollution by Cd+2.

Cation-Stress-Responsive Transcription Factors SltA and CrzA Regulate Morphogenetic Processes and Pathogenicity of Colletotrichum gloeosporioides.

Growth of Colletotrichum gloeosporioides in the presence of cation salts NaCl and KCl inhibited fungal growth and anthracnose symptom of colonization. Previous reports indicate that adaptation of Aspergillus nidulans to salt- and osmotic-stress conditions revealed the role of zinc-finger transcription factors SltA and CrzA in cation homeostasis. Homologs of A. nidulans SltA and CrzA were identified in C. gloeosporioides. The C. gloeosporioides CrzA homolog is a 682-amino acid protein, which contains a C2H2 zinc finger DNA-binding domain that is highly conserved among CrzA proteins from yeast and filamentous fungi. The C. gloeosporioides SltA homolog encodes a 775-amino acid protein with strong similarity to A. nidulans SltA and Trichoderma reesei ACE1, and highest conservation in the three zinc-finger regions with almost no changes compared to ACE1 sequences. Knockout of C. gloeosporioides crzA (ΔcrzA) resulted in a phenotype with inhibited growth, sporulation, germination and appressorium formation, indicating the importance of this calciu006D-activated transcription factor in regulating these morphogenetic processes. In contrast, knockout of C. gloeosporioides sltA (ΔsltA) mainly inhibited appressorium formation. Both mutants had reduced pathogenicity on mango and avocado fruit. Inhibition of the different morphogenetic stages in the ΔcrzA mutant was accompanied by drastic inhibition of chitin synthase A and B and glucan synthase, which was partially restored with Ca2+ supplementation. Inhibition of appressorium formation in ΔsltA mutants was accompanied by downregulation of the MAP kinase pmk1 and carnitine acetyl transferase (cat1), genes involved in appressorium formation and colonization, which was restored by Ca2+ supplementation. Furthermore, exposure of C. gloeosporioides ΔcrzA or ΔsltA mutants to cations such as Na+, K+ and Li+ at concentrations that the wild type C. gloeosporioides is not affected had further adverse morphogenetic effects on C. gloeosporioides which were partially or fully restored by Ca2+. Overall results suggest that both genes modulating alkali cation homeostasis have significant morphogenetic effects that reduce C. gloeosporioides colonization.

Mechanisms of divalent metal toxicity in affective disorders.

Metals are required for proper brain development and play an important role in a number of neurobiological functions. The divalent metal transporter 1 (DMT1) is a major metal transporter involved in the absorption and metabolism of several essential metals like iron and manganese. However, non-essential divalent metals are also transported through this transporter. Therefore, altered expression of DMT1 can modify the absorption of toxic metals and metal-induced toxicity. An accumulating body of evidence has suggested that increased metal stores in the brain are associated with elevated oxidative stress promoted by the ability of metals to catalyze redox reactions, resulting in abnormal neurobehavioral function and the progression of neurodegenerative diseases. Metal overload has also been implicated in impaired emotional behavior, although the underlying mechanisms are not well understood with limited information. The current review focuses on psychiatric dysfunction associated with imbalanced metabolism of metals that are transported by DMT1. The investigations with respect to the toxic effects of metal overload on behavior and their underlying mechanisms of toxicity could provide several new therapeutic targets to treat metal-associated affective disorders.

Carvacrol protects neuroblastoma SH-SY5Y cells against Fe(2+)-induced apoptosis by suppressing activation of MAPK/JNK-NF-κB signaling pathway.

AIM: Carvacrol (2-methyl-5-isopropylphenol), a phenolic monoterpene in the essential oils of the genera Origanum and Thymus, has been shown to exert a variety of therapeutic effects. Here we examined whether carvacrol protected neuroblastoma SH-SY5Y cells against Fe(2+)-induced apoptosis and explored the underlying mechanisms. METHODS: Neuroblastoma SH-SY5Y cells were incubated with Fe(2+) for 24 h, and the cell viability was assessed with CCK-8 assay. TUNEL assay and flow cytometric analysis were performed to evaluate cell apoptosis. The mRNA levels of pro-inflammatory cytokines and NF-κB p65 were determined using qPCR. The expression of relevant proteins was determined using Western blot analysis or immunofluorescence staining. RESULTS: Treatment of SH-SY5Y cells with Fe(2+) (50-200 µmol/L) dose-dependently decreased the cell viability, which was significantly attenuated by pretreatment with carvacrol (164 and 333 µmol/L). Treatment with Fe(2+) increased the Bax level and caspase-3 activity, and decreased the Bcl-2 level, resulting in cell apoptosis. Furthermore, treatment with Fe(2+) significantly increased the gene expression of IL-1ß, IL-6 and TNF-α, and induced the nuclear translocation of NF-κB. Treatment with Fe(2+) also significantly increased the phosphorylation of p38, ERK, JNK and IKK in the cells. Pretreatment with carvacrol significantly inhibited Fe(2+)-induced activation of NF-κB, expression of the pro-inflammatory cytokines, and cell apoptosis. Moreover, pretreatment with carvacrol inhibited Fe(2+)-induced phosphorylation of JNK and IKK, but not p38 and ERK in the cells. CONCLUSION: Carvacrol protects neuroblastoma SH-SY5Y cells against Fe(2+)-induced apoptosis, which may result from suppressing the MAPK/JNK-NF-κB signaling pathways.

Application of Polymeric Nanoparticles for CNS Targeted Zinc Delivery In Vivo.

A dyshomeostasis of zinc ions has been reported for many psychiatric and neurodegenerative disorders including schizophrenia, attention deficit hyperactivity disorder, depression, autism, Parkinson's and Alzheimer's disease. Furthermore, alterations in zinc-levels have been associated with seizures and traumatic brain injury. Thus, altering zinclevels within the brain is emerging as a new target for the prevention and treatment of psychiatric and neurological diseases. However, given the restriction of zinc uptake into the brain by the blood-brain barrier, methods for controlled regulation and manipulation of zinc concentrations within the brain are rare. Here, we performed in vivo studies investigating the possibility of brain targeted zinc delivery using zinc-loaded nanoparticles which are able to cross the blood-brain barrier. After injecting these nanoparticles, we analyzed the regional and time-dependent distribution of zinc and nanoparticles within the brain. Moreover, we evaluated whether the presence of zinc-loaded nanoparticles alters the expression of zinc sensitive genes and proteins such as metallothioneins and zinc transporters and quantified possible toxic effects. Our results show that zinc loaded g7 nanoparticles offer a promising approach as a novel non - invasive method to selectively enrich zinc in the brain within a small amount of time.

Heavy metal ions affecting the removal of polycyclic aromatic hydrocarbons by fungi with heavy-metal resistance.

The co-occurrence of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) is very common in contaminated environments. It is of paramount importance and great challenge to exploit a bioremediation to remove PAHs in these environments with combined pollution. We approached this question by probing the influence of HMs coexisting with PAHs on the removal of PAHs by Acremonium sp. P0997 possessing metal resistance. A removal capability for naphthalene, fluorene, phenanthrene, anthracene, and fluoranthenepresentalone (98.6, 99.3, 89.9, 60.4, and 70 %, respectively) and in a mixture (96.9, 71.8, 67.0, 85.0, and 87.9 %, respectively) was achieved in mineral culture inoculated with Acremonium sp. P0997, and this strain also displayed high resistance to the individual HMs (Mn(2+), Fe(2+), Zn(2+), Cu(2+), Al(3+), and Pb(2+)). The removal of individual PAHs existing in a mixture was differently affected by the separately tested HMs. Cu(2+)enhanced the partition process of anthracene to dead or alive mycelia and the contribution of the biosorption by this strain but imposed a little negative influence on the contribution of biodegradation to the total removal of anthracene individually in a culture. However, Mn(2+) had an inhibitory effect on the partition process of anthracene to dead or alive mycelia and decreased the contributions of both biosorption and biodegradation to the total anthracene removal. This work showcased the value of fungi in bioremediation for the environments with combined pollution, and the findings have major implications for the bioremediation of organic pollutants in metal-organic mixed contaminated sites.

Polyhydroxyfullerene binds cadmium ions and alleviates metal-induced oxidative stress in Saccharomyces cerevisiae.

The water-soluble polyhydroxyfullerene (PHF) is a functionalized carbon nanomaterial with several industrial and commercial applications. There have been controversial reports on the toxicity and/or antioxidant properties of fullerenes and their derivatives. Conversely, metals have been recognized as toxic mainly due to their ability to induce oxidative stress in living organisms. We investigated the interactive effects of PHF and cadmium ions (Cd) on the model yeast Saccharomyces cerevisiae by exposing cells to Cd (≤5 mg liter(-1)) in the absence or presence of PHF (≤500 mg liter(-1)) at different pHs (5.8 to 6.8). In the absence of Cd, PHF stimulated yeast growth up to 10.4%. Cd inhibited growth up to 79.7%, induced intracellular accumulation of reactive oxygen species (ROS), and promoted plasma membrane disruption in a dose- and pH-dependent manner. The negative effects of Cd on growth were attenuated by the presence of PHF, and maximum growth recovery (53.8%) was obtained at the highest PHF concentration and pH. The coexposure to Cd and PHF decreased ROS accumulation up to 36.7% and membrane disruption up to 30.7% in a dose- and pH-dependent manner. Two mechanisms helped to explain the role of PHF in alleviating Cd toxicity to yeasts: PHF decreased Cd-induced oxidative stress and bound significant amounts of Cd in the extracellular medium, reducing its bioavailability to the cells.

Surfactants present complex joint effects on the toxicities of metal oxide nanoparticles.

The potential toxicities of nanoparticles (NPs) have been intensively discussed over the past decade. In addition to their single toxicities, NPs can interact with other environmental chemicals and thereby exert joint effects on biological systems and the environment. The present study investigated the combined toxicities of NPs and surfactants, which are among the chemicals that most likely coexist with NPs. Photobacterium phosphoreum was employed as the model organism. The results indicate that surfactants with different ion types can alter the properties of NPs (i.e., particle size and surface charge) in different ways and present complex joint effects on NP toxicities. Mixtures of different NPs and surfactants exhibited antagonistic, synergistic, and additive effects. In particular, the toxicity of ZnO was observed to result from its dissolved Zn(2+); thus, the joint effects of the ZnO NPs and surfactants can be explained by the interactions between the Zn ions and the surfactants. Our study suggests that the potential hazards caused by mixtures of NPs and surfactants are different from those caused by single NPs. Because surfactants are extensively used in the field of nanotechnology and are likely to coexist with NPs in natural waters, the ecological risk assessments of NPs should consider the impacts of surfactants.

Long-term effects of Ni(II) on the performance and activity of activated sludge processes.

The long-term effects of Ni(II) on substrate removal and microorganism activities were investigated by operating sequencing batch reactors (SBRs). Compared to the control system lacking Ni(II), the removal efficiencies of total organic carbon (TOC) and ammonium nitrogen (NH4(+)-N) in SBR system loading with 10mgL(-1) Ni(II) decreased drastically from 90.2±3.6 percent to 75.0±8.9 percent, and 99.2±0.6 percent to 50.8±11.5 percent, respectively. As compared to the control system, a inhibitory rate of more than 50 percent for the 2,3,5-triphenyltetrazolium chloride electron transport system (TTC-ETS) and the 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride electron transport system (INT-ETS), and 43 percent for the specific oxygen uptake rate (sOUR) were detected in SBR system loading with 20mgL(-1) Ni(II). TTC-ETS, INT-ETS, and sOUR were significantly correlated with substrate removal efficiencies, suggesting that they could all serve as effective indicators of the performance of activated sludge processes. Additionally, INT-ETS is superior to sOUR and TTC-ETS in detecting the toxic effects of Ni(II) on sludge microorganism activity.

Modelling the effects of copper on soil organisms and processes using the free ion approach: towards a multi-species toxicity model.

The free ion approach has been previously used to calculate critical limit concentrations for soil metals based on point estimates of toxicity. Here, the approach was applied to dose-response data for copper effects on seven biological endpoints in each of 19 European soils. The approach was applied using the concept of an effective dose, comprising a function of the concentrations of free copper and 'protective' major cations, including H(+). A significant influence of H(+) on the toxicity of Cu(2+) was found, while the effects of other cations were inconsistent. The model could be generalised by forcing the effect of H(+) and the slope of the dose-response relationship to be equal for all endpoints. This suggests the possibility of a general bioavailability model for copper effects on organisms. Furthermore, the possibility of such a model could be explored for other cationic metals such as nickel, zinc, cadmium and lead.

Modeling rhizotoxicity and uptake of Zn and Co singly and in binary mixture in wheat in terms of the cell membrane surface electrical potential.

The usually negative, but variable electrical potential (ψ0) at the cell membrane (CM) surface influences the surface activities of free ions and the electrical driving force for the transport of ions across the CM. The rhizotoxic effects and uptake of Zn(2+) and Co(2+) singly and in binary mixture in wheat ( Triticum aestivum L.) at three pH values (4.5, 5.5, or 6.1) were examined in terms of the free ion activities of Zn(2+), Co(2+), and H(+) at the CM surface (these ions are denoted {M(n+)}(0)). Toxicity and uptake of Zn(2+) or Co(2+) singly to roots were better correlated with {M(2+)}(0) than with their bulk-phase activities. Studies of toxicant interactions using the electrostatic approach and a response-multiplication model for toxicant mixtures indicated that {Co(2+)}(0) significantly enhanced the toxicity of {Zn(2+)}(0), but {Zn(2+)}(0) did not significantly affect the toxicity of {Co(2+)}(0). {H(+)}(0) substantially enhanced the toxicity of both metal ions. Taking ψo into account improved the correspondence (denoted r(2)) between observed and predicted uptake of both Zn(2+) and Co(2+), and each inhibited the uptake of the other. Results showed that r(2) increased from 0.776 to 0.936 for Zn uptake and improved from 0.805 to 0.951 for Co uptake. Thus electrostatic models for metal toxicity and uptake proved superior to models incorporating only bulk-phase activities of ions.

Modeling toxicity of binary metal mixtures (Cu(2+) -Ag(+) , Cu(2+) -Zn(2+) ) to lettuce, Lactuca sativa, with the biotic ligand model.

The biotic ligand model (BLM) was applied to predict metal toxicity to lettuce, Lactuca sativa. Cu(2+) had the lowest median effective activity (EA50(M) ), compared with Ag(+) and Zn(2+) (EA50(Cu) = 2.60 × 10(-8) M, EA50(Ag) = 1.34 × 10(-7) M, EA50(Zn) = 1.06 × 10(-4) M). At the 50% response level, the fraction of the total number of biotic ligands occupied by ions (f50(M) ) was lowest for Ag(+) among the metals (f50(Ag) = 0.22, f50(Cu) = 0.36, f50(Zn) = 0.42). Cu(2+) had the highest affinity for biotic ligands compared with Ag(+) and Zn(2+) , as shown by stability constants of the cation-biotic ligand binding, expressed as log K(MBL) (log K(CuBL) = 7.40, log K(AgBL) = 6.39, log K(ZnBL) = 4.00). Furthermore, the BLM was combined with the toxic equivalency factor approach in predicting toxicity of mixtures of Cu(2+) -Zn(2+) and Cu(2+) -Ag(+) . The fraction of biotic ligands occupied by ions was used to determine the relative toxic potency of metals and the toxic equivalency quotient (TEQ) of mixtures. This approach allowed for including interactions in estimating mixture toxicity and showed good predictive power (r(2) = 0.64-0.84). The TEQ at the 50% response level (TEQ50, Cu(2+) equivalents) for Cu(2+) -Zn(2+) mixtures was significantly lower than the value for Cu(2+) -Ag(+) mixtures. Joint toxicity depended on both TEQ and specific composition of the mixture. The present study supports the use of the accumulation of metal ions at the biotic ligands as a predictor of toxicity of single metals and mixtures.

Role in metal homeostasis of CtpD, a Co²âº transporting P(1B4)-ATPase of Mycobacterium smegmatis.

Genetic studies in the tuberculosis mouse model have suggested that mycobacterial metal efflux systems, such as the P(1B4)-ATPase CtpD, are important for pathogenesis. The specificity for substrate metals largely determines the function of these ATPases; however, various substrates have been reported for bacterial and plant P(1B4)-ATPases leaving their function uncertain. Here we describe the functional role of the CtpD protein of Mycobacterium smegmatis. An M. smegmatis mutant strain lacking the ctpD gene was hypersensitive to Co²âº and Ni²âº and accumulated these metals in the cytoplasm. ctpD transcription was induced by both Co²âº and superoxide stress. Biochemical characterization of heterologously expressed, affinity-purified CtpD showed that this ATPase is activated by Co²âº, Ni²âº and to a lesser extend Zn²âº (20% of maximum activity). The protein was also able to bind one Co²âº, Ni²âº or Zn²âº to its transmembrane transport site. These observations indicate that CtpD is important for Co²âº and Ni²âº homeostasis in M. smegmatis, and that M. tuberculosis CtpD orthologue could be involved in metal detoxification and resisting cellular oxidative stress by modulating the intracellular concentration of these metals.

Physiological metal uptake by Nostoc punctiforme.

Trace metals are required for many cellular processes. The acquisition of trace elements from the environment includes a rapid adsorption of metals to the cell surface, followed by a slower internalization. We investigated the uptake of the trace elements Co(2+), Cu(2+), Mn(2+), Ni(2+), and Zn(2+) and the non-essential divalent cation Cd(2+) in the cyanobacterium Nostoc punctiforme. For each metal, a dose response study based on cell viability showed that the highest non-toxic concentrations were: 0.5 µM Cd(2+), 2 µM Co(2+), 0.5 µM Cu(2+), 500 µM Mn(2+), 1 µM Ni(2+), and 18 µM Zn(2+). Cells exposed to these non-toxic concentrations with combinations of Zn(2+) and Cd(2+), Zn(2+) and Co(2+), Zn(2+) and Cu(2+) or Zn(2+) and Ni(2+), had reduced growth in comparison to controls. Cells exposed to metal combinations with the addition of 500 µM Mn(2+) showed similar growth compared to the untreated controls. Metal levels were measured after one and 72 h for whole cells and absorbed (EDTA-resistant) fractions and used to calculate differential uptake rates for each metal. The differences in binding and internalisation between different metals indicate different uptake processes exist for each metal. For each metal, competitive uptake experiments using (65)Zn showed that after 72 h of exposure Zn(2+) uptake was reduced by most metals particularly 0.5 µM Cd(2+), while 2 µM Co(2+) increased Zn(2+) uptake. This study demonstrates that N. punctiforme discriminates between different metals and favourably substitutes their uptake to avoid the toxic effects of particular metals.

A time course assessment of changes in reactive oxygen species generation and antioxidant defense in hydroponically grown wheat in response to lead ions (Pb2+).

We examined the effect of Pb(2+) (8 and 40 mg l(-1)) on reactive oxygen species generation and alterations in antioxidant enzymes in hydroponically grown wheat at 24, 72, and 120 h after exposure. Pb(2+) toxicity was more pronounced on root growth, and it correlated with the greater Pb accumulation in roots. Pb exposure (40 mg l(-1)) enhanced superoxide anion, H(2)O(2), and MDA content in wheat roots by 1.9- to 2.2-folds, 56-255%, and 41-90%, respectively, over the control. Pb-induced loss of membrane integrity was confirmed by the enhanced electrolyte leakage and in vivo histochemical localization. Activities of scavenging enzymes, superoxide dismutases and catalases, enhanced in Pb-treated wheat roots by 1.4- to 5.7-folds over that in the control. In contrast, the activities of ascorbate and guaiacol peroxidases and glutathione reductases decreased significantly, suggesting their non-involvement in detoxification process. The study concludes that Pb(2+)-induced oxidative damage in wheat roots involve greater H(2)O(2) accumulation and the deactivation of the related scavenging enzymes.

Reproduction of aquatic hyphomycetes at low concentrations of Ca2+, Zn2+, Cu2+, and Cd2+.

Maple leaf disks were conditioned in a stream for three weeks and then aerated for 2 d in distilled water to induce fungal sporulation. The release of aquatic hyphomycete spores increased when the water was supplemented with low concentrations of Ca(2+) (5 µg/L), Zn(2+) (2.5 µg/L), Cu(2+) (0.5 µg/L), or Cd(2+) (0.125 µg/L). Higher supplement concentrations inhibited sporulation. Over the concentration range used, the sporulation response was generally best described by a quadratic regression, suggesting a biphasic or hormetic response. A similar pattern was found with the number of fungal species as the dependent variable. Anguillospora filiformis and Anguillospora longissima were generally least inhibited by metal supplements, and Ca(2+) was the least and Cd(2+) the most toxic metal. Combinations of metals had a more severe effect on fungal sporulation than predicted from addition of the effects of the metals in isolation. The biological significance of the hormetic response is unclear; however, acknowledging it is clearly relevant for establishing guidelines or recommendations in toxicology.