Nickel in the terrestrial environment

Variability of the Ionome of Wild Boar (Sus scrofa) and Red Deer (Cervus elaphus) in a Dutch National Park, with Implications for Biomonitoring

The ionome-an important expression of the physiological state of organisms-is poorly known for mammals. The focus on particular tissues-such as liver, kidney, and bones-in biomonitoring of environmental pollution and potential deficiencies is based on widely held assumptions rather than solid knowledge of full mammalian ionomes. We examined the full ionome of Red deer (Cervus elaphus) and Wild boar (Sus scrofa), two commonly used mammals for biomonitoring, in a Dutch protected nature reserve (Veluwezoom). We used four individuals per species. We dissected 13 tissues and organs from each individuals (eight in total) of each species and measured 22 elemental concentrations in each. We assessed, for each element, how concentrations varied across tissues within and between individuals. Based on existing literature, we put our findings in the context of their function in the mammalian body. We found that the ionome was highly variable between as well as within the two species. For most elements, tissues containing the highest and lowest concentration differed between individuals. No single tissue accurately represented the accumulation of toxic elements or potential deficiencies in the bodies. Our assessment of the element's biological roles revealed a serious lack of reference values. Our findings imply that analyses of commonly used tissues in biomonitoring do not necessarily capture bioaccumulation of toxins or potential deficiencies. We recommend establishing a centralized database of mammalian ionomes to derive reference values in future. To our knowledge, our study is one of the most complete assessments of mammalian ionomes to date.

Nickel sources affect soil biological properties but do not affect sorghum growth

Nickel (Ni) is an essential element, but it can be phytotoxic in high concentration, which may be caused by high availability in soil solution. The objective of this study was to evaluate the effect of sources and doses of Ni applied to a dystrophic Red Latosol cultivated with sorghum on i) the availability of the metal in the soil; ii) the impact on biological and biochemical properties of the soil; iii) the absorption and distribution in sorghum plants; and iv) crop productivity. The experiment was carried out within a completely randomized design with two nickel sources [nickel(II) nitrate, Ni(NO3)2 and nickel(III) oxide, Ni2O3], three doses (35, 70, and 140 mg Ni kg-1 soil), plus controls without Ni, with 3 replications. The concentrations of Ni in the soil, soil microbial biomass (SMB), basal soil respiration (BSR), metabolic quotient (qCO2), fluorescein diacetate (FDA) hydrolysis, and urease activity were determined. The concentrations of Ni in the leaf diagnostic and in the plant (shoot, root, and grains) were also measured. In the soil, the concentrations of available Ni remained between 0.21 and 54.01 mg Ni kg-1. Ni2O3 contributed very little to the increase in available Ni. SMB and the FDA hydrolysis were not affected by the Ni source or Ni dose, but BSR and qCO2 had significant increase with Ni application rates, suggesting the soil microorganisms faced stress. Soil urease activity was affected by Ni dose but not by Ni source. The dose of Ni as Ni(NO3)2 decreased the metal concentration in the plant, while that of Ni2O3 increased it. Nickel source did not affect dry mass production of the plants, but grain yield was affected in a dose-dependent manner when Ni2O3 was the source of Ni.

Supplementation of nitric oxide and spermidine alleviates the nickel stress-induced damage to growth, chlorophyll metabolism, and photosynthesis by upregulating ascorbate-glutathione and glyoxalase cycle functioning in tomato

Experiments were conducted to evaluate the role of exogenously applied nitric oxide (NO; 50 µM) and spermidine (Spd; 100 µM) in alleviating the damaging effects of Ni (1 mM NiSO46H2O) toxicity on the growth, chlorophyll metabolism, photosynthesis, and mineral content in tomato. Ni treatment significantly reduced the plant height, dry mass, and the contents of glutamate 1-semialdehyde, δ-amino levulinic acid, prototoporphyrin IX, Mg-prototoporphyrin IX, total chlorophyll, and carotenoids; however, the application of NO and Spd alleviated the decline considerably. Supplementation of NO and Spd mitigated the Ni-induced decline in photosynthesis, gas exchange, and chlorophyll fluorescence parameters. Ni caused oxidative damage, while the application of NO, Spd, and NO+Spd significantly reduced the oxidative stress parameters under normal and Ni toxicity. The application of NO and Spd enhanced the function of the antioxidant system and upregulated the activity of glyoxalase enzymes, reflecting significant reduction of the oxidative effects and methylglyoxal accumulation. Tolerance against Ni was further strengthened by the accumulation of proline and glycine betaine due to NO and Spd application. The decrease in the uptake of essential mineral elements such as N, P, K, and Mg was alleviated by NO and Spd. Hence, individual and combined supplementation of NO and Spd effectively alleviates the damaging effects of Ni on tomato.

Assessment of Pb and Ni and potential health risks associated with the consumption of vegetables grown on the roadside soils in District Swat, Khyber Pakhtunkhwa, Pakistan

Vegetables cultivated near roads absorb toxic metals from polluted soil, which enter the human body through the food chain and cause serious health problems to humans. The present study investigated the concentration of lead (Pb) and nickel (Ni) in soils and vegetables grown along the roadside of District Swat, Pakistan, and the health risks associated with the consumption of the tested vegetables. In results, Pb concentration was higher in plants located at the distance between 0-10 m away from the roadside than the WHO permissible limit. In such plants, Pb concentration was higher than Ni. Rumex dentatus contained the highest concentration of Pb (75.63 mg kg^-1 DW) among the tested vegetables while Ni concentration (27.57 mg kg^-1 DW) was highest in Trachyspermum ammi as compared to other plants. Concentration and accumulation of both the metals decreased in soil and plants with increasing distance from the road. Similarly, target hazard quotient values noted for Pb (up to 3.37) were greater than unity, which shows that there is a potential risk associated with the consumption of tested vegetables near the road. Moreover, the values of target cancer risk (up to 0.8413) were greater than 0.0001, which shows that there is a risk of cancer with the consumption of tested vegetables. In conclusion, the consumption of tested vegetables was very dangerous as it may lead to higher risks of cancer. Strict regulatory control is recommended on the cultivation of these vegetables along the roadside to avoid any contamination due to roadside exhaust.

Metal homeostasis in pathogenic Epsilonproteobacteria: mechanisms of acquisition, efflux, and regulation

Epsilonproteobacteria are a diverse class of eubacteria within the Proteobacteria phylum that includes environmental sulfur-reducing bacteria and the human pathogens, Campylobacter jejuni and Helicobacter pylori. These pathogens infect and proliferate within the gastrointestinal tracts of multiple animal hosts, including humans, and cause a variety of disease outcomes. While infection of these hosts provides nutrients for the pathogenic Epsilonproteobacteria, many hosts have evolved a variety of strategies to either sequester metals from the invading pathogen or exploit the toxicity of metals and drive their accumulation as an antimicrobial strategy. As a result, C. jejuni and H. pylori have developed mechanisms to sense changes in metal availability and regulate their physiology in order to respond to either metal limitation or accumulation. In this review, we will discuss the challenges of metal availability at the host-pathogen interface during infection with C. jejuni and H. pylori and describe what is currently known about how these organisms alter their gene expression and/or deploy bacterial virulence factors in response to these environments.

Natural and anthropogenic sources of lead, zinc, and nickel in sediments of Lake Izabal, Guatemala

Sediments in Lake Izabal, Guatemala, contain substantial lead (Pb), zinc (Zn), and nickel (Ni). The lack of historical data for heavy metal concentrations in the sediments makes it difficult to determine the sources or evaluate whether inputs of metals to the lake have changed through time. We measured the relative abundances and concentrations of Pb, Zn, and Ni by X-Ray Fluorescence core scanning and by Inductively Coupled Plasma Optical Emission Spectrometry in three sediment cores to explore stratigraphic distributions of metals in the lake deposits. High amounts of Pb and Zn in the core taken near the Polochic Delta suggest that galena and sphalerite mining increased Pb and Zn delivery to Lake Izabal between ~1945 and 1965 CE. An up-core Ni increase in the core taken near a different mine on the north shore of Lake Izabal suggests that recent nickel mining operations led to an increase in Ni concentrations in the local sediments, but amounts in the other cores indicate that Ni is not widely distributed throughout the lake. Sediment cores from Lake Izabal are reliable recorders of heavy metal input to the lake, and were measured to establish background metal levels, which would otherwise be unavailable. Concentrations of Pb, Zn, and Ni in older, pre-20th-century Lake Izabal sediments reflect input from natural erosion of bedrock. Our results provide previously unavailable estimates of background metal concentrations in Lake Izabal before the onset of mining. These results are necessary for future monitoring related to mining contamination of the lake ecosystem.

Nickel allergy in lipid transfer protein sensitized patients: Prevalence and clinical features

Nickel (Ni), the main responsible for allergic contact dermatitis worldwide, is also involved in systemic condition called "Systemic Nickel Sulfate Allergy Syndrome (SNAS)." Likewise, IgE-mediated reactivity to Lipid Transfer Protein (LTP) represents the main cause of primary food allergy in adults of Mediterranean countries. We evaluated the prevalence of SNAS in LTP allergic patients and investigated patients' clinical features with double sensitization (LTP and Ni). A retrospective, single-center, observational study was conducted performing a complete allergological work-up including: (1) skin prick tests; (2) serum specific IgE for plant food allergens and rPru p3 (LTP); (3) patch test with 5% Ni sulfate in petrolatum. We enrolled 140 LTP allergic patients of which 36 patients (25.7% of sample) showed additional positivity to Ni patch test. Patients with double sensitization were more frequently females and reported fewer cutaneous symptoms. Higher values of sIgE for peach, apple, peanut, walnut, grain, corn, and garlic were found in LTP allergic patients, while higher values for hazelnut in the other subgroup. The prevalence of SNAS in the LTP allergic population is clinically relevant. Moreover, the clinical and immunological profiles of patients with double sensitization were different from patients monosensitized to LTP.

Nickel Toxicity Induced Changes in Nutrient Dynamics and Antioxidant Profiling in Two Maize (Zea mays L.) Hybrids

Nickel (Ni) is among the essential micronutrient heavy metals utilized by plants. However, an elevated level of Ni causes serious concerns for plants’ physiology and their survival. This study evaluated the mechanisms influencing the growth, physiology, and nutrient dynamics in two commercial maize hybrids (Syngenta and Pioneer) exposed to Ni treatments in hydroponics nutrient solution (NS). Seedlings were raised in plastic trays with quartz sand, and subsequently transferred to Hoagland’s NS at the two leaves stage. After three days of transplantation, Ni levels of 0, 20, and 40 mg L⁻¹ were maintained in the nutrient solution. After 30 days of Ni treatments, seedlings were harvested and different growth, physiological, and nutrient concentrations were determined. The results showed that with increasing Ni concentration, the growth of maize hybrids was significantly reduced, and the maize hybrid, Pioneer, showed significantly higher growth than that of Syngenta at all levels of Ni. Higher growth in Pioneer is ascribed to elevated levels of antioxidant enzymes (SOD, CAT, GR, APX, and POX), lower damage to cellular membranes (i.e., higher MSI and lower MDA), and higher tissue nutrient concentrations (N, P, K, Ca, Mg, Fe, Mn, Zn, and Cu). Furthermore, the maize hybrids showed a difference in nutrient translocation from root to shoot which could be one of the factors responsible for differential response of these hybrids against Ni treatments.

Nickel toxicity in plants: reasons, toxic effects, tolerance mechanisms, and remediation possibilities-a review

Nickel (Ni) is a naturally occurring metal, but anthropogenic activities such as industrialization, use of fertilizers, chemicals, and sewage sludge have increased its concentration in the environment up to undesirable levels. Ni is considered to be essential for plant growth at low concentration; however, Ni pollution is increasing in the environment, and therefore, it is important to understand its functional roles and toxic effects on plants. This review emphasizes the environmental sources of Ni, its essentiality, effects, tolerance mechanisms, possible remediation approaches, and research direction that may help in interdisciplinary studies to assess the significance of Ni toxicity. Briefly, Ni affects plant growth both positively and negatively, depending on the concentration present in the growth medium. On the positive side, Ni is essential for normal growth, enzymatic activities (e.g., urease), nitrogen metabolism, iron uptake, and specific metabolic reactions. On the negative side, Ni reduces seed germination, root and shoot growth, biomass accumulation, and final production. Moreover, Ni toxicity also causes chlorosis and necrosis and inhibits various physiological processes (photosynthesis, transpiration) and cause oxidative damage in plants. The threat associated with Ni is increased as Ni concentration increases day by day in the environment, particularly in soils; therefore, it would be hazardous for crop production in the near future. Additionally, the lack of information regarding the mechanisms of Ni tolerance in plants further intensifies this situation. Therefore, future research should be focused on approachable and prominent solutions in order to minimize the entry of Ni into our ecosystems.

Biogeochemical behavior of nickel under different abiotic stresses: toxicity and detoxification mechanisms in plants

Nickel (Ni) is a ubiquitous and highly important heavy metal. At low levels, Ni plays an essential role in plants such as its role in urease, superoxide dismutase, methyl-coenzyme M reductase, hydrogenase, acetyl-coenzyme A synthase, and carbon monoxide dehydrogenase enzyme. Although its deficiency in crops is very uncommon, but in the past few years, many studies have demonstrated Ni deficiency symptoms in plants. On the other hand, high levels of applied Ni can provoke numerous toxic effects (such as biochemical, physiological, and morphological) in plant tissues. Most importantly, from an ecological and risk assessment point of view, this metal has narrow ranges of its essential, beneficial, and toxic concentrations to plants, which significantly vary with plant species. This implies that it is of great importance to monitor the levels of Ni in different environmental compartments from which it can enter plants. Additionally, several abiotic stresses (such as salinity and drought) have been reported to affect the biogeochemical behavior of Ni in the soil-plant system. Thus, it is also important to assess Ni behavior critically under different abiotic stresses, which can greatly affect its role being an essential or toxic element. This review summarizes and critically discusses data about sources, bioavailability, and adsorption/desorption of Ni in soil; its soil-plant transfer and effect on other competing ions; accumulation in different plant tissues; essential and toxic effects inside plants; and tolerance mechanisms adopted by plants under Ni stress.

Phytoremediation of Ni-contaminated soil by Salicornia iranica

Although nickel (Ni) is useful and is used in various industries, it is one of the most usual and important sources of heavy metals pollutants in the world. In this study, Salicornia iranica was used in order to phytoremediate Ni-contaminated soil. Possible mechanisms of plant tolerance to Ni pollution and its detoxification were studied through using expression analysis of glutathione-S-transferase (GST) and measurement of involved key physiological components. The concentration of the chlorophylls a, b, total chlorophyll, and carotenoids were significantly decreased in 500 mg/kg Ni at 3, 24, 48 h, and 90 days after the treatment. Free proline significantly increased in the tissues. The absorption and concentration of Ni increased in tissues, so that Ni concentration at 50, 250, and 500 mg Ni/kg soil significantly increased to 2.5, 3.5, and 4.5 fold compared with the lowest Ni level respectively. In addition, the GST expression was significantly increased both in the 50 and 500 mg/kg Ni treatment. The highest concentration of Ni affected plant growth parameters such as the root and shoot lengths. Therefore, S. iranica is able to accumulate Ni and it can be used as an environmental biotechnological study for phytoremediation of Ni-polluted soils. Abbreviations: ABA: abscisic acid; ABRE: ABA-responsive element; As⁺³: arsenic; Cd²⁺: cadmium; ef1: elongation factor; FW: fresh weight; GSH: glutathione; GST: glutathione-S-transferase; GSTU: tau class GST; Hcl: hydrochloric acid; Hg²⁺: mercury; HgCl₂: mercury(II) chloride; MYB: myeloblastosis viral oncogene homolog; Ni⁺²: nickel; Pb: lead; SiGSTU: Salicornia iranica GSTU; ZnSO₄: zinc sulfate.

Leaves, berries and herbivorous larvae of bilberry Vaccinium myrtillus as sources of metals in food chains at a Cu-Ni smelter site

Ericaceous dwarf shrubs, such as bilberry, Vaccinium myrtillus, have an important role in nutrient cycling of boreal forests, but in metal polluted environments they also form a link between heavy metal pool of the soil, primary consumers and upper trophic levels. From the viewpoint of metal transfer in a food chain, we document metallic element (As, Ca, Cd, Co, Cu, Mn, Mo, Ni, Pb, Se, Zn) concentrations in leaves, berries and herbivorous larvae of V. myrtillus around a Finnish copper-nickel smelter and compare those with levels in relatively unpolluted reference sites, and with levels documented in soil and feces (a proxy of dietary levels) of an insectivorous bird, the pied flycatcher, Ficedula hypoleuca. Herbivorous larvae of the autumnal moth, Epirrita autumnata (Lepidoptera: Geometridae), grown experimentally on V. myrtillus, showed slower growth rate but not higher mortality in the polluted area. In general, metal levels in leaves, berries and larvae were higher in the polluted area and comparable to those reported at other smelter sites in Europe. The levels of the main toxic metals (As, Cd, Cu, Ni, Pb) followed the general pattern: soil > bird feces > leaves > larvae = berries, and levels in V. myrtillus, E. autumnata and F. hypoleuca reflected soil metal levels. The lowest levels were found in those matrices that are most important sources of food for birds and humans, i.e. leaf-eating larvae and berries, reducing a risk of toxic effects.

Role of Ni-tolerant Bacillus spp. and Althea rosea L. in the phytoremediation of Ni-contaminated soils

In our current study, four nickel-tolerant (Ni-tolerant) bacterial species viz, Bacillus thuringiensis 002, Bacillus fortis 162, Bacillus subtilis 174, and Bacillus farraginis 354, were screened using Ni-contaminated media. The screened microbes exhibited positive results for synthesis of indole acetic acid (IAA), siderophore production, and phosphate solubilization. The effects of these screened microbes on Ni mobility in the soil, root elongation, plant biomass, and Ni uptake in Althea rosea plants grown in Ni-contaminated soil (200 mg Ni kg^-1) were evaluated. Significantly higher value for water-extractable Ni (38 mg kg^-1) was observed in case of Ni-amended soils inoculated with B. subtilis 174. Similarly, B. thuringiensis 002, B. fortis 162, and B. subtilis 174 significantly enhanced growth and Ni uptake in A. rosea. The Ni uptake in the shoots and roots of B. subtilis 174-inoculated plants enhanced up to 1.7 and 1.6-fold, respectively, as compared to that in the un-inoculated control. Bacterial inoculation also significantly improved the root and shoot biomass of treated plants. The current study presents a novel approach for bacteria-assisted phytoremediation of Ni-contaminated areas.

The Nickel Concentration in Breast Milk during the First Month of Lactation in Yazd, Center of Iran

Breastfeeding plays an important role in the growth and development of breastfed infants, especially in the first 6 months of their lives. The present study was conducted to determine the nickel concentrations in breast milk of lactating women in Yazd, Iran. One hundred fifty volunteers were selected among nursing mothers referring to health centers in Yazd. In the first month of lactation, milk samples were collected three times, on days 3 to 5 (first), 16 (Second), and 30 (third) after delivery. Nickel concentration of the samples was measured by atomic absorption spectrophotometer. Demographic variables were collected through a questionnaire which was completed by mothers. The mean age of the study group was 27.40 ± 4.66 years. The mean nickel concentrations in breast milk at the first, second, and third samples were 47.3 ± 7.40, 49.9 ± 8.05, and 54.8 ± 7.38 μg/l, respectively. The concentration of nickel in the breast milk of more than 86 % of mothers was higher than the permissible range for it. There was no significant relationship between the mean value of nickel in breast milk and education, age, and job of mothers. High level of nickel in breast milk may be attributed to consumed food and drinking water containing nickel. Monitoring the nickel level in breast milk regularly is recommended.

Nickel sensitization in patients with gastro-esophageal reflux disease

BACKGROUND

Gastro-esophageal reflux disease (GERD) leads to frequent medical visits, and available therapies fail in up to 40% of patients. Food allergies may be involved in GERD pathogenesis; however, allergens other than food have received little attention. Nickel allergy is common in the general population and some high-nickel foods are associated with GERD. However, the potential relationship between nickel allergy and GERD remains unaddressed.

AIM

This study aimed to evaluate the prevalence of nickel sensitization in patients with and without GERD and to compare clinical and demographic features.

METHODS

This prospective, multicenter study included 210 adult GERD patients and 140 patients without GERD who presented at the general practitioner. All GERD patients had undergone treatment with proton pump inhibitors and upper digestive endoscopy within the previous five years. Demographic and clinical data were collected by questionnaire and patients underwent a nickel patch allergy test.

RESULTS

Patients with and without GERD presented similar characteristics, with the exception of nickel sensitization, which was significantly more prevalent among GERD patients than controls (39.5% vs. 16.4%; p = 0.001). Nickel-positive GERD patients were more frequently female (90.4% vs. 65.4%, p = 0.003) and asthmatic (18.1% vs. 4.7%; p = 0.038), compared to nickel-negative GERD patients. At six-month follow-up, most of the patients, with or without nickel sensitization, reported improved symptoms without differences in drug prescription.

CONCLUSION

Nickel sensitization is particularly prevalent in GERD patients seen in general practice. Whether allergies other than food allergy play a role in GERD remains to be elucidated.

A Comparative Study on the Uptake and Toxicity of Nickel Added in the Form of Different Salts to Maize Seedlings

In soil ecotoxicological studies, a toxic metal is usually added in the form of either an inorganic or organic salt with relatively high solubility. Nitrate, chloride, acetate, or sulfate are commonly considered as valid options for that aim. However, recent studies have shown that different salts of the same metal at the same cationic concentration may exhibit different toxicities to plants and soil organisms. This information should be considered when selecting data to use for developing toxicological criteria for soil environment. A comparative study was carried out to evaluate the toxicity of five nickel (Ni) salts: NiCl₂, NiSO₄, Ni(II)-citrate, Ni(CH₃COO)₂, and Ni(II)-EDTA (ethylenediaminetetraacetate), on maize seedlings. The plant metrics used were plant height, shoot and root biomass, leaf soluble sugars and starch, and the Ni contents of the shoots and roots. The results indicated that when Ni was added to the soil, toxicity varied with the selected anionic partner with the following toxicity ranking NiSO₄ < Ni(CH₃COO)₂ < Ni(II)-citrate < NiCl₂ < Ni(II)-EDTA. Taking the plant-height metric as an example, the effective concentrations for 50% inhibition (EC₅₀) were 3148 mg·kg⁻¹ for NiSO₄, 1315 mg·kg⁻¹ for NiCl₂, and 89 mg·kg⁻¹ for Ni(II)-EDTA. Compared with the Ni in the other salts, that in Ni(II)-EDTA was taken up the most efficiently by the maize roots and, thus, resulted in the greatest toxic effects on the plants. Nickel generally reduced leaf soluble sugars, which indicated an effect on plant carbohydrate metabolism. The outcome of the study demonstrates that different salts of the same metal have quite different ecotoxicities. Therefore, the anionic counterpart of a potentially toxic metal cation must be taken into account in the development of ecotoxicological criteria for evaluating the soil environment, and a preferred approach of leaching soil to reduce the anionic partner should also be considered.

Nickel detoxification and plant growth promotion by multi metal resistant plant growth promoting Rhizobium species RL9

Pollution of the biosphere by heavy metals is a global threat that has accelerated dramatically since the beginning of industrial revolution. The aim of the study is to check the resistance of RL9 towards the metals and to observe the effect of Rhizobium species on growth, pigment content, protein and nickel uptake by lentil in the presence and absence of nickel. The multi metal tolerant and plant growth promoting Rhizobium strain RL9 was isolated from the nodules of lentil. The strain not only tolerated nickel but was also tolerant o cadmium, chromium, nickel, lead, zinc and copper. The strain tolerated nickel 500 μg/mL, cadmium 300 μg/mL, chromium 400 μg/mL, lead 1,400 μg/mL, zinc 1,000 μg/mL and copper 300 μg/mL, produced good amount of indole acetic acid and was also positive for siderophore, hydrogen cyanide and ammonia. The strain RL9 was further assessed with increasing concentrations of nickel when lentil was used as a test crop. The strain RL9 significantly increased growth, nodulation, chlorophyll, leghaemoglobin, nitrogen content, seed protein and seed yield compared to plants grown in the absence of bioinoculant but amended with nickel The strain RL9 decreased uptake of nickel in lentil compared to plants grown in the absence of bio-inoculant. Due to these intrinsic abilities strain RL9 could be utilized for growth promotion as well as for the remediation of nickel in nickel contaminated soil.

Interactive effect of calcium and gibberellin on nickel tolerance in relation to antioxidant systems in Triticum aestivum L

Nickel toxicity affects many metabolic facets of plants and induces anatomical and morphological changes resulting in reduced growth and productivity. To overcome the damaging effects of nickel (Ni) stress, different strategies of the application of nutrients with plant hormones are being adopted. The present experiment was carried out to assess the growth and physiological response of wheat plant (Triticum aestivum L.) cv. Samma to pre-sowing seed treatment with GA(3) alone as well as in combination with Ca(2+) and/or Ni stress. The pre-sowing seed treatment of Ni decreased all the growth characteristics (plant height, root length, fresh, and dry weight) as well as chlorophyll (Chl) content and enzyme carbonic anhydrase (CA: E.C. 4.2.1.1) activity. However, an escalation was recorded in malondialdehyde content and electrolyte leakage in plants raised from seed soaked with Ni alone. Moreover, all the growth parameters and physiological attributes (Chl content, proline (Pro) content, CA, peroxidase (E.C.1.11.1.7), catalase (E.C. 1.11.1.6), superoxide dismutase (E.C. 1.15.1.1), ascorbate peroxidase (E.C. 1.11.1.11), and glutathione reductase (E.C. 1.6.4.2) were enhanced in the plants developed from the seeds soaked with the combination of GA(3) (10(-6) M), Ca(2+), and Ni. The present study showed that pre-sowing seed treatment of GA(3) with Ca(2+) was more capable in mitigation of adverse effect of Ni toxicity by improving the antioxidant system and Pro accumulation.

Phytotoxic effects of nickel on yield and concentration of macro- and micro-nutrients in sunflower (Helianthus annuus L.) achenes

The phytotoxic effects of varying levels of nickel (0, 10, 20, 30, and 40 mg L(-1)) on growth, yield and accumulation of macro- and micro-nutrients in leaves and achenes of sunflower (Helianthus annuus L.) were appraised in this study. A marked reduction in root and shoot fresh biomass was recorded at higher Ni levels. Nickel stress also caused a substantial decrease in all macro- and micro-nutrients in leaves and achenes. The lower level of Ni (10 mg L(-1)) had a non-significant effect on various yield attributes, but higher Ni levels considerably decreased these parameters. Higher Ni levels decreased the concentrations of Ca, Mn and Fe in achenes. In contrast, achene N, K, Zn, Mn and Cu decreased consistently with increasing level of Ni, even at lower level (10 mg L(-1)). Sunflower hybrid Hysun-33 had better yield and higher most of the nutrients in achenes as compared with SF-187. The maximum reduction in all parameters was observed at the maximum level of nickel (40 mg L(-1)) where almost all parameters were reduced more than 50% of those of control plants. In conclusion, the pattern of uptake and accumulation of different nutrients in sunflower plants were nutrient- and cultivar-specific under Ni-stress.

Nickel: an overview of uptake, essentiality and toxicity in plants

Nickel even though recognized as a trace element, its metabolism is very decisive for certain enzyme activities, maintaining proper cellular redox state and various other biochemical, physiological and growth responses. Study of the aspects related with uptake, transport and distributive localization of Ni is very important in various cellular metabolic processes particularly under increased nitrogen metabolism. This review article, in core, encompasses the dual behavior of Ni in plants emphasizing its systemic partitioning, essentiality and ill effects. However, the core mechanism of molecules involved and the successive physiological conditions required starting from the soil absorption, neutralization and toxicity generated is still elusive, and varies among the plants.

Essential roles and hazardous effects of nickel in plants

With the world's ever increasing human population, the issues related to environmental degradation of toxicant chemicals are becoming more serious. Humans have accelerated the emission to the environment of many organic and inorganic pollutants such as pesticides, salts, petroleum products, acids, heavy metals, etc. Among different environmental heavy-metal pollutants, Ni has gained considerable attention in recent years, because of its rapidly increasing concentrations in soil, air, and water in different parts of the world. The main mechanisms by which Ni is taken up by plants are passive diffusion and active transport. Soluble Ni compounds are preferably absorbed by plants passively, through a cation transport system; chelated Ni compounds are taken up through secondary, active-transport-mediated means, using transport proteins such as permeases. Insoluble Ni compounds primarily enter plant root cells through endocytosis. Once absorbed by roots, Ni is easily transported to shoots via the xylem through the transpiration stream and can accumulate in neonatal parts such as buds, fruits, and seeds. The Ni transport and retranslocation processes are strongly regulated by metal-ligand complexes (such as nicotianamine, histidine, and organic acids) and by some proteins that specifically bind and transport Ni. Nickel, in low concentrations, fulfills a variety of essential roles in plants, bacteria, and fungi. Therefore, Ni deficiency produces an array of effects on growth and metabolism of plants, including reduced growth, and induction of senescence, leaf and meristem chlorosis, alterations in N metabolism, and reduced Fe uptake. In addition, Ni is a constituent of several metallo-enzymes such as urease, superoxide dismutase, NiFe hydrogenases, methyl coenzyme M reductase, carbon monoxide dehydrogenase, acetyl coenzyme-A synthase, hydrogenases, and RNase-A. Therefore, Ni deficiencies in plants reduce urease activity, disturb N assimilation, and reduce scavenging of superoxide free radical. In bacteria, Ni participates in several important metabolic reactions such as hydrogen metabolism, methane biogenesis, and acetogenesis. Although Ni is metabolically important in plants, it is toxic to most plant species when present at excessive amounts in soil and in nutrient solution. High Ni concentrations in growth media severely retards seed germinability of many crops. This effect of Ni is a direct one on the activities of amylases, proteases, and ribonucleases, thereby affecting the digestion and mobilization of food reserves in germinating seeds. At vegetative stages, high Ni concentrations retard shoot and root growth, affect branching development, deform various plant parts, produce abnormal flower shape, decrease biomass production, induce leaf spotting, disturb mitotic root tips, and produce Fe deficiency that leads to chlorosis and foliar necrosis. Additionally, excess Ni also affects nutrient absorption by roots, impairs plant metabolism, inhibits photosynthesis and transpiration, and causes ultrastructural modifications. Ultimately, all of these altered processes produce reduced yields of agricultural crops when such crops encounter excessive Ni exposures.

Reactivity of nickel in soils: evidence of retention kinetics

The bioavailability and mobility of nickel (Ni) is highly dependent on the mechanisms associated with Ni adsorption-desorption and its kinetics in soils. To examine the characteristics of Ni retention and release, kinetic sorption batch experiments were performed on three soils having different properties, followed by Ni desorption using successive dilutions. Sorption of Ni by all soils was highly nonlinear and strongly kinetic, where the rate of Ni retention was rapid initially and was followed by gradual or somewhat slow retention behavior with increasing reaction time. Desorption of Ni was strongly irreversible and hysteretic in nature, indicating lack of equilibrium retention and/or irreversible or slowly reversible processes. A sequential extraction procedure provided evidence that a significant amount of Ni was irreversibly adsorbed on all soils. A nonlinear multireaction model with equilibrium-kinetic-irreversible reaction sites successfully described the retention (adsorption) and subsequent release of Ni on the different soils. The model was also capable of predicting Ni desorption kinetics based on adsorption data sets only.

Extension of coupled multispecies metal transport and speciation (TRANSPEC) model to soil

Atmospheric deposition of metals emitted from mining operations has raised metal concentrations in the surrounding soils. This repository may be remobilized and act as a source of metals to nearby surface aquatic systems. It is important to understand metal dynamics and the impact of various chemistry and fate parameters on metal movement in the soil environment in order to evaluate risk associated with metals in terrestrial ecosystems and accurately establish critical discharge limits that are protective of aquatic biota. Here we extend our previously developed coupled multispecies metal fate-TRANsport and SPECiation/complexation (TRANSPEC) model, which was applicable to surface aquatic systems. The extended TRANSPEC, termed TRANSPEC-II, estimates the partition coefficient, K(d), between the soil-solid and -soluble phases using site-specific data and a semi-empirical regression model obtained from literature. A geochemical model calculates metal and species fractions in the dissolved and colloidal phases of the soil solution. The multispecies fugacity/aquivalence based fate-transport model then estimates inter-media transport rates such as leaching from soil, soil runoff, and water-sediment exchanges of each metal species. The model is illustratively applied to Ni in the Kelly Lake watershed (Sudbury, Ontario, Canada), where several mining operations are located. The model results suggest that the current atmospheric fallout supplies only 4% of Ni removed from soil through soil runoff and leaching. Soil runoff contributes about 20% of Ni entering into Kelly Lake with the rest coming from other sources. Leaching to groundwater, apart from runoff, is also a major loss process for Ni in the soil. A sensitivity analysis indicates that raising soil pH to above 6 may substantially reduce metal runoff and improve water quality of nearby water bodies that are impacted by runoff.

Effect of metal tolerant plant growth promoting Bradyrhizobium sp. (vigna) on growth, symbiosis, seed yield and metal uptake by greengram plants

The nickel and zinc tolerant plant growth promoting Bradyrhizobium sp. (vigna) RM8 was isolated from nodules of greengram, grown in metal contaminated Indian soils. The plant growth promoting (PGP) potentials of strain RM8 was assessed both in the presence and absence of nickel and zinc under in vitro conditions. Strain RM8 tolerated a high level of nickel (300 microg ml(-1)) and zinc (1400 microg ml(-1)) on yeast extract mannitol agar medium. Bradyrhizobium sp. (vigna) strain RM8 produced 13.3 microg ml(-1) of indole acetic acid in Luria Bertani broth at 100 microg ml(-1) of tryptophan which increased to 13.6 microg ml(-1) at 50 microg Ni ml(-1) and 13.5 microg ml(-1) at 300 microg Zn ml(-1). Strain RM8 was positive for siderophore, HCN and ammonia both in the absence and presence of nickel and zinc. The PGP activity of this strain was further evaluated with increasing concentrations of nickel and zinc using greengram as a test crop. The bioinoculant enhanced the nodule numbers by 82%, leghaemoglobin by 120%, seed yield by 34%, grain protein by 13%, root N by 41% and shoot N by 37% at 290 mg Ni kg(-1) soil. At 4890 mg Zn kg(-1) soil, the bioinoculant increased the nodule numbers by 50%, leghaemoglobin by 100%, seed yield by 36%, grain protein by 13%, root N by 47% and shoot N by 42%. The bioinoculant strain RM8 reduced the uptake of nickel and zinc by plant organs compared to plants grown in the absence of bioinoculant. This study suggested that the bioinoculant due to its intrinsic abilities of growth promotion and attenuation of the toxic effects of nickel and zinc could be exploited for remediation of metal from nickel and zinc contaminated sites.

Tolerance of transgenic canola plants (Brassica napus) amended with plant growth-promoting bacteria to flooding stress at a metal-contaminated field site

The growth of transgenic canola (Brassica napus) expressing a gene for the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase was compared to non-transformed canola exposed to flooding and elevated soil Ni concentration, in situ. In addition, the ability of the plant growth-promoting bacterium Pseudomonas putida UW4, which also expresses ACC deaminase, to facilitate the growth of non-transformed and transgenic canola under the above mentioned conditions was examined. Transgenic canola and/or canola treated with P. putida UW4 had greater shoot biomass compared to non-transformed canola under low flood-stress conditions. Under high flood-stress conditions, shoot biomass was reduced and Ni accumulation was increased in all instances relative to low flood-stress conditions. This is the first field study to document the increase in plant tolerance utilizing transgenic plants and plant growth-promoting bacteria exposed to multiple stressors.

Significance of Bacillus subtilis strain SJ-101 as a bioinoculant for concurrent plant growth promotion and nickel accumulation in Brassica juncea

In this study, a nickel (Ni)-tolerant Bacillus subtilis strain SJ-101 was characterized based on the 16SrDNA homology and phylogenetic analysis. The role of this strain ascertained in facilitating Ni accumulation in the Indian mustard plant (Brassica juncea [L]. Czern and Coss) var. Pusa Bold (DIR-50), to elucidate the potential of Ni phytoremediation in combination with metal-tolerant rhizobacteria. The data revealed that the plants exposed to NiCl2 (1750 mg kg(-1)) in soil bioaugmented with strain SJ-101 have accumulated 0.147% Ni vis-à-vis 0.094% accumulation in dry biomass of the plants grown in uninoculated soil. The strain SJ-101 has also exhibited the capability of producing indole acetic acid (IAA) (55 microg ml(-1)), and solubilizing inorganic phosphate (90 microg ml(-1)) in specific culture media. The pot culture experiments clearly demonstrated the beneficial effects of bioinoculant strain SJ-101 with significant increase (p<0.05) in the plant growth attributes in untreated control soil. Furthermore, the protective effect of the strain SJ-101 against Ni phytotoxicity was evident in plants grown in soil treated with NiCl2 in concentration range of 250-1750 mg kg(-1). Thus, it is suggested that the strain SJ-101 owing to its intrinsic abilities of plant growth promotion, and attenuation of soil Ni by biosorption and bioaccumulation, could be exploited for bacteria-assisted phytoaccumulation of this toxic heavy metal from contaminated sites.

Nickelophilous plants and their significance in phytotechnologies

Nickeliferous soils are invaded predominantly by members of the Brassicaceae, Cyperaceae, Cunoniaceae, Caryophyllaceae, Fabaceae, Flacourtiaceae, Euphorbiaceous, Lamiaceae, Poaceae and Violaceae, and many of these plants are metal tolerant. About 300 Ni hyperaccumulating plants been identified. These members exhibit unusual appetite for toxic metals and elemental defense. Hyperaccumulators provide protection against fungal and insect attack. Investigations suggested that Ni-hyperaccumulation has a protective function against fungal and bacterial pathogens in Streptanthus polygaloides and Thlaspi montanum. Significance of nickelophilous plants and their significance in phytotechnologies are discussed in this paper.

Characterization and nickel sorption kinetics of a new metal hyper-accumulator Bacillus sp

The heavy metal-resistant bacterial strain SJ-101 has been isolated from fly ash contaminated soil. Based on the morphological and biochemical characteristics, the isolate SJ-101 was presumptively identified as Bacillus sp. The adsorption isotherms revealed the absolute adsorption capacity (Q degrees) of 244 mg Ni g(-1) dry cell mass vis-à-vis 161 mg Ni g(-1) synthetic resin (Amberlite IR-120). The higher relative adsorption capacity (K(F)) of 7.37, and the intensity of adsorption (1/n) of 0.58 with dry cell biomass suggested higher affinity of Bacillus cells towards nickel ions. The data conform to the Langmuir adsorption model relatively better than the Freundlich model. The thermodynamic parameters indicated the feasibility, endothermic, and interactive nature of nickel adsorption process on the cell surface. Higher Ni tolerance and sorption capacity of Bacillus sp. SJ-101, explicitly signifies its implications in Ni bioremediation process.

Mineral content in legumes and nuts: contribution to the Spanish dietary intake

We evaluated the levels of essential elements as Cu, Cr, Fe and Zn, and toxic elements as Al, Ni, Pb and Cd in a total of 40 samples of different legumes and 56 samples of different nuts, that are widely consumed in Spain. These elements were determined in the samples mineralized with HNO(3) and V(2)O(5), using electrothermal atomic absorption spectrometry (ETAAS) as the analytical technique. Reliability of the procedure was checked by analysis of a certified reference material. No matrix effects were observed and aqueous standard solutions were used for calibration. In legumes, the levels ranged from 1.5-5.0 microg Cu/g, 0.05-0.60 microg Cr/g, 18.8-82.4 microg Fe/g, 32.6-70.2 microg Zn/g, 2.7-45.8 microg Al/g, 0.02-0.35 microg Ni/g, 0.32-0.70 microg Pb/g and not detectable-0.018 microg Cd/g. In nuts, the levels ranged from 4.0-25.6 microg Cu/g, 0.25-1.05 microg Cr/g, 7.3-75.6 microg Fe/g, 25.6-69.0 microg Zn/g, 1.2-20.1 microg Al/g, 0.10-0.64 microg Ni/g, 0.14-0.39 microg Pb/g, and not detectable-0.018 microg Cd/g. A direct statistical correlation between Cu-Cr, Zn-Al and Cr-Ni (P<0.05), and Al-Pb (P<0.001), has been found. The growing popularity of these products in recent years on the basis of its nutritional properties and beneficial effects, requires additional data and a periodical control. In addition, the present findings are of potential use to food composition tables.

Heavy metals and metalloids in egg contents and eggshells of passerine birds from Arizona

Concentrations of inorganic elements were determined in eggs of passerine birds including the endangered southwestern willow flycatcher (Empidonax traillii extimus) from four regions in Arizona. The main aim of the study was to determine the distribution of metals in egg contents and eggshells, with emphasis on the deposition of Sr in eggshells. Seventy eggs of 11 passerine species were collected at four nesting locations during 2000. Aluminum, Ba, Cr, Cu, Mn, Se, Sr, and Zn, were detected primarily in egg contents of all bird species. Arsenic, Ni, Pb, and V were detected primarily in eggshells. A proportion of most inorganic elements accumulated in the eggshell. Concentrations of Ba, Cu, Mn, Se, Sr, and Zn in egg contents and As, Ba, Cu, and V in eggshells of yellow-breasted chats (Icteria virens) were similar among locations. However, concentrations of Mn, Ni, Sr, and Zn in eggshells were significant different among locations. Except for Cu, Mn, Se, and Zn, concentrations of inorganic elements were 2-35 times greater in eggshells than in eggs. Most concentrations of metals and metalloids in eggs and eggshells of all the bird species were below levels known to affect reproduction or that have other deleterious effects. However, I found somewhat elevated concentrations of Sr in eggshells (highest MEAN=1505 microg/g dw, n=3) of yellow-breasted chats and willow flycatchers, and in egg contents of yellow warblers (Dendroica petechia) and song sparrows (Melospiza melodia). Whether current observed concentrations of Sr in eggshells are affecting nesting birds in Arizona remains to be determined. Strontium and other metals could be associated with lower hatching success in some areas. This study shows that a proportion of many inorganic elements accumulates in the eggshell and that the potential effects on the proper structure and functioning of the eggshell should not be ignored.

Evidence for high affinity nickel transporter genes in heavy metal resistant Streptomyces spec

We have isolated 25 new strains of streptomycetes from soil samples of a polluted site at the former uranium mine, Wismut, in eastern Thuringia, Germany. The strains grew on medium containing 1 mM NiCl2 and thus were resistant to the heavy metal ion. Seven of the strains were further characterized. All of these strains were resistant to heavy metals in various degrees with up to 10 mM resistance against NiCl2 supplied with the liquid minimal growth medium. The high level of resistance prompted us to look for high affinity nickel transporter genes thought to provide a means to eliminate the excess nickel ions form the cells. Degenerate oligonucleotide primers derived from sequences of P-type ATPase transporter genes of Gram negative bacteria identified a fragment which shows deduced amino acid sequence similarities to known high affinity nickel transporters. Investigation of two genes obtained from the isolates Streptomyces spec. E8 and F4 showed high sequence divergence. This was unexpected since a transmissible plasmid had been thought to convey heavy metal resistance.

Stress indications in copper- and nickel-exposed Scots pine seedlings

Scots pine nursery seedlings were planted in pots, five seedlings per treatment, and placed in an experimental field at the University of Oulu in northern Finland at the beginning of June 1997. Copper and nickel sulphates were mixed with forest mineral soil before seedling planting. The metal levels ranged from 0 to 25 mg Ni kg(-1) dry soil and 0 to 50 mg Cu kg(-1) in dry soil and in combinations of both metals. Current year's needles for element analyses, EDS microanalyses, microscopy and glutathione and peroxidase activity analyses were collected from 1-5 seedlings per treatment in September. Seedling biomass in controls, Cu25 and Cu50 differed significantly from the Ni25Cu50 treatment. The root/shoot ratio was highest in the Ni5 treatment, indicating good root growth, though the roots were visibly healthier in the Cu25 treatment than in the Ni5 treatment. At higher Ni levels, the condition of roots deteriorated. The proportion of plasmolysed mesophyll cells was highest in the Ni25 treatment. Copper-treated seedlings did not suffer from Cu stress, because no severe injuries were seen in either the roots or the needles in Cu-exposed seedlings. The needle concentrations of Cu increased only slightly due to treatments. Ni accumulation in needles increased with increasing concentrations in soil. Needles of Cu-treated seedlings had less oxidized glutathione than those of Ni-treated seedlings, but the roots had higher, not significantly, peroxidase activity levels. Light-colored, swollen thylakoids were occasionally observed in the Ni25Cu50 treatment, indicating some interaction between Ni and Cu. Ni seemed to cause more oxidative stress to the seedlings than copper, which was manifested as a decreased GSH level and an increased proportion of GSSG in the Ni treatments. Copper together with nickel strongly decreased root growth, the root/shoot ratio being lowest in the Ni25Cu50 treatment.

Saturation of ecosystems with toxic metals in Sudbury basin, Ontario, Canada

Mining and resource recovery activities have not been kind to ecosystems in the Sudbury basin, Ontario. The combination of logging, smelting, fires and erosion resulted in an unusual anthropogenic ecosystem of denuded barren land with lifeless lakes, or a micro-desert. Since the 1970s, however, the concerted efforts made to reduce the emissions and rehabilitate parts of the degraded ecosystem have resulted in improvements in water quality, and recoveries in phytoplankton, zooplankton, zoobenthos and fish communities but have had little impact on toxic metal concentrations in many lakes. We show that most of the catchments in the Sudbury basin have become saturated with Cu and Ni, and some with Zn and Pb. It is estimated that mobilization of metals stored in soils and glacial overburden by surface runoff, groundwater drainage and wind re-working of tailings can sustain the high concentrations of Cu and Ni in many lakes for well over 1000 years. Strategies to immobilize the pollutant metals in the watershed rather than further emission controls may be required for dealing with high levels of toxic metals in surface waters of the saturated ecosystems.