Ni Toxicity Research Articles

The bifunctional transcription factor NAC32 modulates nickel toxicity responses through repression of root-nickel compartmentalization and activation of auxin biosynthesis

Nickel (Ni) is an important micronutrient, but excess Ni is toxic to many plant species. Currently, relatively little is known about the genetic basis of the plant responses to Ni toxicity. Here, we demonstrate that NAC32 transcription factor functions as a core genetic hub to regulate the Ni toxicity responses in Arabidopsis. NAC32 negatively regulates root-Ni concentration through the IREG2 (IRON REGULATED2) encoding a transporter. NAC32 also induces local auxin biosynthesis in the root-apex transition zone by upregulating YUCCA 7 (YUC7)/8/9 expression, which results in a local enhancement of auxin signaling in root tips, especially under Ni toxicity, thereby impaired primary root growth. By analyses of various combinations of nac32 and ireg2 mutants, as well as nac32 and yuc7/8/9 triple mutants, including high-order quadruple mutant, we demonstrated that NAC32 negatively regulates Ni stress tolerance by acting upstream of IREG2 and YUC7/8/9 to modulate their function in Ni toxicity responses. ChIPqPCR, EMSA (electrophoretic mobility shift assay) and transient dual-LUC reporter assays showed that NAC32 transcriptionally represses IREG2 expression but activates YUC7/8/9 expression by directly binding to their promoters. Our work demonstrates that NAC32 coordinates Ni compartmentation and developmental plasticity in roots, providing a conceptual framework for understanding Ni toxicity responses in plants.

Individual and combinatorial application of nanosilica and carbon nanoparticles alleviate nickel stress in barley (Hordeum vulgare L.): Impacts on gene expression, AsA − GSH cycle, cellular fractionation, and proline metabolism

Nanotechnology is grabbing great attention all over the world because of its stimulating use in numerous fields, and the nanosilica (nSi) and carbon nanoparticles (CNPs) application has been examined in various studies. Conversely, the nSi and CNPs combinatorial use is a new method and researched in limited literature. For this purpose, a pot experiment was conducted to examine various growth and biochemical parameters in barley (Hordeum vulgare L.) under the toxic concentration of nickel (Ni) i.e., 200 mg kg−1 which were primed with combined application of two NPs of nSi at 3 mM and CNPs i.e., 200 μM respectively. The results showed that the Ni toxicity in the soil showed a significantly (P < 0.05) declined in the growth, gas exchange attributes, sugars, AsA-GSH cycle, cellular fractionation, proline metabolism in H. vulgare. However, Ni toxicity significantly (P < 0.05) increased oxidative stress biomarkers, enzymatic and nonenzymatic antioxidants including their gene expression in H. vulgare. Although, the application of nSi and CNPs showed a significant (P < 0.05) increase in the plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds and their gene expression and also decreased the oxidative stress, and Ni uptake. In addition, individual or combined application of nSi and CNPs enhanced the cellular fractionation and decreases the proline metabolism and AsA−GSH cycle in H. vulgare. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of heavy metal contamination in agricultural soils.

Impact of Nickel Toxicity on Growth, Fruit Quality and Antioxidant Response in Zucchini Squash (Cucurbita pepo L.).

The impact of trace metal elements (TMEs) on plants is one current pollution problem, the severity of which is increasing with industrial development, population growth and inappropriate agricultural practices. The latter can have irreversible effects on ecosystems, including species extinction, trophic chain contamination and altered human health, particularly in the case of consumed plants such as zucchini squash (Cucurbita pepo L.). This study aims to investigate the effects of nickel on various physiological and biochemical parameters of zucchini growth, with a particular focus on how this toxic metal impacts the quality of fruit that is consumed by humans. To achieve this, plants aged 45 days were grown for one month on solid media loaded with different concentrations of Ni (0, 100, 300 and 500 µM). The results showed that exposure of plants to Ni resulted in significantly altered growth and higher accumulation of Ni in the shoots (1314 µg·g-1 DW) than in roots and fruits. Concerning non-enzymatic antioxidants, the results showed that Ni toxicity significantly increased total polyphenols, especially in shoots at 300 µM Ni, while flavonoid content decreased in the roots and shoots in response to Ni treatment. Our results also show that nickel tolerance in C. pepo is ensured by a combination of several mechanisms such as an increase in the content of proline. This species can survive and tolerate, to different degrees, toxic cations at concentrations up to 500 µM but with visible symptoms of toxicity such as chlorosis of the leaves. Indeed, based on thresholds of hyperaccumulation, we can qualify Cucurbita pepo as a hyperaccumulator species of nickel.

Nickel-induced oxidative stress and phospholipid remodeling in cucumber leaves

Nickel phytotoxicity has been attributed, among others, to oxidative stress. However, little is known about Ni-induced phospholipid modifications, including the oxidative ones. Accumulation of reactive oxygen species (ROS), antioxidative enzyme activities, malondialdehyde and the early lipid oxidation products contents, membrane permeability, phospholipid profile as well as phospholipid unsaturation degree were studied in the 1st and the 2nd leaves of hydroponically grown cucumber seedlings subjected to Ni stress. Compared to the 2nd leaf the 1st one showed stronger visual Ni toxicity symptoms, higher Ni, O2.- and H2O2 accumulation as well as greater enhancement in membrane permeability. Enzyme activities were differently influenced by Ni stress, however most pronounced changes were generally found in the 1st leaf. Ni treatment resulted in oxidation of leaf lipids, which was evidenced by appearance of increased contents of MDA and the early produced oxylipins. Among the latter 9-hydroxyoctadecatrienoic acid (9-HOTrE) and 13-hydroxyoctadecatrienoic acid (13-HOTrE) contents showed the most pronounced increase in response to Ni treatment. Exposure to the metal led to the changes in the leaf phospholipid profile and increased degree of phospholipid unsaturation. The obtained results have been discussed in relation to the difference in Ni stress severity between the 1st and the 2nd leaves.

Transcriptomics pave the way into mechanisms of cobalt and nickel toxicity: Nrf2-mediated cellular responses in liver carcinoma cells

Cobalt (Co) and Nickel (Ni) are used nowadays in various industrial applications like lithium-ion batteries, raising concerns about their environmental release and public health threats. Both metals are potentially carcinogenic and may cause neurological and cardiovascular dysfunctions, though underlying toxicity mechanisms have to be further elucidated. This study employs untargeted transcriptomics to analyze downstream cellular effects of individual and combined Co and Ni toxicity in human liver carcinoma cells (HepG2). The results reveal a synergistic effect of Co and Ni, leading to significantly higher number of differentially expressed genes (DEGs) compared to individual exposure. There was a clear enrichment of Nrf2 regulated genes linked to pathways such as glycolysis, iron and glutathione metabolism, and sphingolipid metabolism, confirmed by targeted analysis. Co and Ni exposure alone and combined caused nuclear Nrf2 translocation, while only combined exposure significantly affects iron and glutathione metabolism, evidenced by upregulation of HMOX-1 and iron storage protein FTL. Both metals impact sphingolipid metabolism, increasing dihydroceramide levels and decreasing ceramides, sphingosine and lactosylceramides, along with diacylglycerol accumulation. By combining transcriptomics and analytical methods, this study provides valuable insights into molecular mechanisms of Co and Ni toxicity, paving the way for further understanding of metal stress.

Unveiling the potential of A. fabrum and γ-aminobutyric acid for mitigation of nickel toxicity in fenugreek

Nickel (Ni) is a heavy metal that adversely affects the growth of different crops by inducing oxidative stress and nutrient imbalance. The role of rhizobacteria (RB) is vital to resolve this issue. They can promote root growth and facilitate the uptake of water and nutrients, resulting in better crop growth. On the other hand, γ-aminobutyric acid (GABA) can maintain the osmotic balance and scavenge the reactive oxygen species under stress conditions. However, the combined effect of GABA and RB has not been thoroughly explored to alleviate Ni toxicity, especially in fenugreek plants. Therefore, in the current pot study, four treatments, i.e., control, A. fabrum (RB), 0.40 mM GABA, and 0.40 mM GABA + RB, were applied under 0Ni and 80 mg Ni/kg soil (80Ni) stress. Results showed that RB + 0.40 mM GABA caused significant improvements in shoot length (~ 13%), shoot fresh weight (~ 47%), shoot dry weight (~ 47%), root length (~ 13%), root fresh weight (~ 60%), and root dry weight (~ 15%) over control under 80 Ni toxicity. A significant enhancement in total chlorophyll (~ 14%), photosynthetic rate (~ 17%), stomatal CO2 concentration (~ 19%), leaves and roots N (~ 10 and ~ 37%), P (~ 18 and ~ 7%) and K (~ 11 and ~ 30%) concentrations, while a decrease in Ni (~ 83 and ~ 49%) concentration also confirmed the effectiveness of RB + 0.40 mM GABA than control under 80Ni. In conclusion, fabrum + 0.40 mM GABA can potentially alleviate the Ni toxicity in fenugreek plants. The implications of these findings extend to agricultural practices, environmental remediation efforts, nutritional security, and ecological impact. Further research is recommended to elucidate the underlying mechanisms, assess long-term effects, and determine the practical feasibility of using A. fabrum + 0.40GABA to improve growth in different crops under Ni toxicity.

Physiological and molecular bases of the nickel toxicity responses in tomato

Nickel (Ni), a component of urease, is a micronutrient essential for plant growth and development, but excess Ni is toxic to plants. Tomato (Solanum lycopersicum L.) is one of the important vegetables worldwide. Excessive use of fertilizers and pesticides led to Ni contamination in agricultural soils, thus reducing yield and quality of tomatoes. However, the molecular regulatory mechanisms of Ni toxicity responses in tomato plants have largely not been elucidated. Here, we investigated the molecular mechanisms underlying the Ni toxicity response in tomato plants by physio-biochemical, transcriptomic and molecular regulatory network analyses. Ni toxicity repressed photosynthesis, induced the formation of brush-like lateral roots and interfered with micronutrient accumulation in tomato seedlings. Ni toxicity also induced reactive oxygen species accumulation and oxidative stress responses in plants. Furthermore, Ni toxicity reduced the phytohormone concentrations, including auxin, cytokinin and gibberellic acid, thereby retarding plant growth. Transcriptome analysis revealed that Ni toxicity altered the expression of genes involved in carbon/nitrogen metabolism pathways. Taken together, these results provide a theoretical basis for identifying key genes that could reduce excess Ni accumulation in tomato plants and are helpful for ensuring food safety and sustainable agricultural development.

Nickel Effects on Growth and Phytolith Yield of Grasses in Contaminated Soils

Nickel (Ni) is extremely toxic to plants at high concentrations. Phytoliths have the potential to sequester the heavy metals absorbed by plants and act as a detoxification mechanism for the plant. The authors of the present study aimed to evaluate the effects of Ni on the growth and phytolith yield of grasses in two artificially contaminated soils. Two experiments separated by soil types (Typic Quartzipsamment and Rhodic Hapludox) were conducted in a completely randomized design in a 2 × 4 factorial scheme with three replications. The factors were two species of grass (Urochloa decumbens and Megathyrsus maximus) and three concentrations of Ni (20, 40, and 120 mg kg−1) and control treatment. The grasses were influenced by the increase in Ni rates in the soils. Ni exerted a micronutrient function with the addition of 30 mg kg−1 of Ni in soils, but this concentration caused toxicity in grasses. Such a level is lower than the limits imposed by the Brazilian environmental legislation. Higher Ni availability in Typic Quartzipsamment promoted Ni toxicity, with reduced growth and increased phytolith yield in the shoot, increased Ni in the shoot, and Ni occlusion in phytoliths by grasses, in comparison with Rhodic Hapludox. The yield and Ni capture in phytoliths by grasses in Ni-contaminated soils are related to the genetic and physiological differences between grasses and Ni availability in soils. Ni capture by phytoliths indicates that it may be one of the detoxification mechanisms of Urochloa decumbens to Ni contamination, providing additional tolerance. Megathyrsus maximus may be a future grass for the phytoremediation technique in Ni-contaminated soils.

Proline-mediated redox regulation in wheat for mitigating nickel-induced stress and soil decontamination

Nickel (Ni) is known as a plant micronutrient and serves as a component of many significant enzymes, however, it can be extremely toxic to plants when present in excess concentration. Scientists are looking for natural compounds that can influence the development processes of plants. Therefore, it was decided to use proline as a protective agent against Ni toxicity. Proline (Pro) is a popularly known osmoprotectant to regulate the biomass and developmental processes of plants under a variety of environmental stresses, but its role in the modulation of Ni-induced toxicity in wheat is very little explored. This investigation indicated the role of exogenously applied proline (10 mM) on two wheat varieties (V1 = Punjab-11, V2 = Ghazi-11) exposed to Ni (100 mg/kg) stress. Proline mediated a positive rejoinder on morphological, photosynthetic indices, antioxidant enzymes, oxidative stress markers, ion uptake were analyzed with and without Ni stress. Proline alone and in combination with Ni improved the growth, photosynthetic performance, and antioxidant capacity of wheat plants. However, Ni application alone exhibited strong oxidative damage through increased H2O2 (V1 = 28.96, V2 = 55.20) accumulation, lipid peroxidation (V1 = 26.09, V2 = 38.26%), and reduced translocation of macronutrients from root to shoot. Application of Pro to Ni-stressed wheat plants enhanced actions of catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), and total soluble protein (TSP) contents by 45.70, 44.06, 43.40, and 25.11% in V1, and 39.32, 46.46, 42.22, 55.29% in V2, compared to control plants. The upregulation of antioxidant enzymes, proline accumulation, and uptake of essential mineral ions has maintained the equilibrium of Ni in both wheat cultivars, indicating Ni detoxification. This trial insight into an awareness that foliar application of proline can be utilized as a potent biochemical method in mitigating Ni-induced stress and might serve as a strong remedial technique for the decontamination of polluted soil particularly with metals.

Alleviating effects of exogenous melatonin on nickel toxicity in two pepper genotypes

The excessive accumulation of nickel (Ni) poses a significant threat to global agricultural productivity. In recent years, it has become clear that melatonin (ME) may play a significant role in protecting plants against heavy metal toxicity. This current study investigates the influence of exogenous ME on mitigating the adverse effects of Ni toxicity in pepper plants. The present results revealed that Ni toxicity significantly hindered pepper seedling growth, damaged the leaf photosynthetic system, impaired pigment concentration, and increased phenolic content. In contrast, ME supplementation efficiently restored seedling growth, protected the photosynthetic system, and further increased the phenolic concentration in pepper leaves. In addition, Ni toxicity considerably increased malondialdehyde (MDA) and hydrogen peroxide (H2O2) production and increased antioxidant enzymes [SOD (superoxide dismutase), CAT (catalase), POD (peroxidase), GR (glutathione reductase), APX (ascorbate peroxidase), and GST (glutathione S-transferase)] activity in pepper leaves and roots. Conversely, ME inhibited MDA and H2O2 accumulation and further increased the antioxidant enzyme activity in pepper leaves and roots. Furthermore, ME application restricted Ni accumulation from root to shoot. Collectively, the ME has shown the ability to mitigate the adverse effects of Ni toxicity in pepper plants. The findings of this study will contribute to the understanding and mitigation of the adverse impacts of Ni-induced stress on the growth and development of plants.

Histological and ionomics assessment to elucidate tolerance mechanisms of nickel-tolerant and sensitive cultivars of bread wheat (Triticum aestivum L.)

Recent literature has raised concerns over crop safety due to nickel (Ni) contamination of irrigation water and agricultural soil in Pakistan. Consequently, wheat crop has suffered in terms of nutrient disbalance and yield reduction. Therefore, it is important to screen tolerant wheat cultivars against Ni toxicity with the ability to accumulate low concentration in grains. In this regard, two wheat cultivars (SKD-1 and Borlaug-16) were exposed to Ni stress (100 mg/L) in a pot experiment for 21 days. In the present study, trace elements (As, Cr, Cu, Cd, Mn, Hg, Ni, Pb, and Zn) and mineral nutrients (Ca, Fe, K, Mg, Na, and P) were tested by ICP-OES. To understand tolerance mechanisms, wheat tissues were tested for morphological parameters, anatomical alteration, oxidative stress, and antioxidant capacity. The translocation of Ni was higher in SKD-1 (0.62) compared to Borlaug-16 (0.45) due to low Ni accumulation in roots of Borlaug-16. In the roots of Borlaug-16, trace elements (Cr, Cu, Mn, Pb, and Zn) were comparatively higher than SKD-1. On the contrary, nutrients (Ca, Fe, Mg, Na, and P) were higher in leaves of SKD-1. Under Ni stress, the root anatomy of Borlaug-16 exhibited a marked increase in the cellular thickness of the cortex by 130.38% and stele by 46.2%. Conversely, the bundle sheath cell thickness rose by 68.36% in the SKD-1. In terms of leaf anatomy, Borlaug-16 showed enhanced thickness in the xylem by 13.01% and bundle sheath cells by 84.95%. Meanwhile, the upper epidermis and phloem of SKD-1 registered thickness increases of 21.80% and 24.47% under Ni stress. Oxidative stress (MDA and H2O2) was comparatively highly induced in SKD-1 tissues compared to Borlaug-16. On the other hand, antioxidants (SOD, CAT, and APX) were comparatively higher in root and leaf tissues of Borlaug-16. The lower Ni uptake, less cellular damage, and high antioxidant capacity of Borlaug-16 makes it more tolerant to Ni stress. Such findings will pave the way towards sustainable crop production.

Inducing Rhizosphere Acidification in White Willow with Bacillus sp. ZV6 Enhances Ni Phytoextraction from Soil and Soil Quality

Chelating agents may decrease the extent of Ni phytoextraction by reducing plant growth and soil health due to Ni toxicity during enhanced phytoextraction. Contrarily, inducing acidity in the rhizosphere of Ni-accumulating plants with plant growth-promoting rhizobacteria (PGPR) having rhizosphere acidification ability can enhance Ni phytoextraction by increasing Ni bioavailability in the soil, plant growth, and plant stress tolerance. We investigated the efficacy of a PGPR species with rhizosphere acidification potential, named Bacillus sp. ZV6 (ARB), in enhancing Ni phytoextraction by white willow (Salix alba) from a Ni-affected soil. The plants were grown for 120 days in soil with zero, threshold, and moderate Ni pollution levels (0, 50, and 100 mg Ni kg−1 soil, respectively) with and without ARB inoculation. After harvest, the effects of the treatments on rhizosphere acidification and associated Ni bioavailability in this zone, Ni distribution in plants, and Ni removal from the soil were investigated. Moreover, enzyme activity, count of bacteria, biomass of microbes, and organic C in the soil, together with indices of plant growth and antioxidant defense, were evaluated. The ARB inoculation significantly improved the plant parameters and soil health and reduced plant oxidative stress at each Ni level compared to the treatments lacking ARB. Besides lowering the soil pH and increasing Ni bioavailability in the rhizosphere with respect to the bulk zone, ARB inoculation exerted additional effects. Surprisingly, the Ni 100 + ARB treatment induced the highest decrease in soil pH (0.32 unit) and an increase in DPTA-extractable Ni (0.45 mg kg−1 soil) between that measured in the bulk zones and that obtained in the rhizosphere zone. Ni distribution in plant parts and Ni removal (% of total Ni) from the soil were also significantly improved with ARB inoculation, compared to the Ni treatments without ARB. The extent of Ni removal was similar for the Ni 50 + ARB (0.27%) and Ni 100 + ARB (0.25%) treatments. Concluding, ARB-inoculated Salix alba can remove similar amounts of Ni from the soil, irrespective of the Ni pollution level.

Exogenously applied sodium nitroprusside alleviates nickel toxicity in maize by regulating antioxidant activities and defense-related gene expression.

Nickel (Ni) stress adversely affects plant growth and biomass accumulation, posturing severe menace to crop production and food security. The current study aimed to determine the putative role of sodium nitroprusside (SNP) in mitigating Ni-induced phytotoxicity and identify the underlying defense mechanisms in maize, which are poorly understood. Our findings showed that SNP significantly augmented plant growth, biomass, and photosynthesis-related attributes (Fv/Fm, Fm, qP ETR, and ΦPSII) through diminishing Ni uptake and translocation in root and shoot tissues of maize under Ni stress conditions. In parallel, exogenous SNP substantially relieved maize seedlings from Ni-induced stress by enhancing enzymatic (SOD, CAT, and GPX) and non-enzymatic (phenol and flavonoids) antioxidant defenses and reducing oxidative stress indicators (MDA and H2 O2 ). The results revealed that SNP treatment increased the content of organic osmolyte glycine betaine and the activity of GST, concomitantly with ATP and ionic exchange capacity (including Ca2+ -ATPase and Mg2+ -ATPase), advocating its sufficiency to promote plant growth and avert Ni-induced stress in maize plants. The only exception was the production of organic acids (citric, oxalic, malic, and formic acids), which was reduced as SNP treatment relieved maize seedlings from Ni-induced oxidative damage. The application of SNP also displayed higher expression of defense- and detoxifying-related genes than in control treatments. Together, our data highlighted the mechanism involved in the amelioration of Ni toxicity by SNP; thus, suggesting a potential role of SNP in mitigating the adverse effects of Ni-contaminated soils to boost growth and yield of crop plants, that is, maize.

Phytohormones and arbuscular mycorrhizal Rhizoglomus intraradices together modulate defense mechanisms in mungbean to reduce Ni toxicity

The roles of Salicylic acid (SA), Nitric Oxide (NO) and Rhizoglomus intraradices in imparting tolerance to Vigna radiata (mungbean) in Nickel (Ni) contaminated soil have been studied individually but not cumulatively. In this study, pot experiments were conducted to compare the individual and synergistic role of phytohormones, with/without R. intraradices in modulating soil properties and curbing the generation of reactive carbonyl species, reactive oxygen species in mungbean plants subjected to Ni (0, 150 mgkg−1) stress. Ni had a negative correlation with growth and productivity potential of plants. Application of phytohormones and arbuscular mycorrhiza (AM) improved the yielding potential by successfully boosting the functioning of enzymes involved in glyoxalase pathway and antioxidant defense system. AM improved the functional efficiency of plants by modulating soil properties and various defense mechanisms to a maximum extent followed by SA and least by NO. Moreover, exogenous application of phytohormones to AM inoculated plants increased the colonisation capacity of fungal partner significantly, which in turn enhanced the synthesis of glomalin and improved the activity of soil enzymes responsible for nutrient cycling. However, combined application of SA with AM functioned in a more synergistic manner than the combined application of NO with AM. Interestingly, the cumulative treatment of the two phytohormones along with R. intraradices was the most efficient in re-establishing mungbean plants under Ni-stress. The study suggested the use of this cost-effective ameliorative strategy involving the combined use of phytohormones with AM to improve the agricultural outputs of mungbean cultivation even under Ni-stressed environments. The study recommends combined applications of phytohormones with AM to impart Ni tolerance to mungbean plants. However, field studies are suggested to be carried out for the authentication of present result findings.

Deterioration of the quality of packaged potable water (bottled water) exposed to sunlight for a prolonged period: An implication for public health.

The exposure of bottled water to sunlight leaches heavy metals into the water, thereby deteriorating its quality and this informed the study. Three plastic bottle brands (n = 100 per brand) were exposed to sunlight for different durations. The leaching of contaminants was exposure duration dependent. The following ranges were recorded for temperature (26.67-29.83 °C), pH (4.73-6.12), conductivity (159.00-298.67 μs/cm), turbidity (0.92-1.22 N.T.U), TDS (98.17-192.77 mg/l), hardness (38.12-78.17 mg/l), Fe (0.01-0.57 mg/l), Mn (BDL - 0.46), Cr (BDL - 0.37 mg/l), Al (BDL - 0.53 mg/l), Cd (0.02-0.21 mg/l), Zn (1.18-9.90 mg/l), Pb (0.03-1.68 mg/l), As (BDL - 1.48 mg/l), and Ni (0.05-1.55 mg/l). Health risk evaluation in all bottled water brands revealed possible Cr, Cd, Pb, As, and Ni toxicity. The carcinogenic risk of Cr, As, and Ni, indicated potential cancer. Arsenic posed the highest non-carcinogenic risk, while Ni posed the highest carcinogenic risk in all brands after 42 days of exposure. The microbial parameters failed to meet the WHO safety limits. The exposure of bottled water to sunlight should be avoided, to ensure a healthy population.

Validation of Nickel Bioavailability Models for Algae, Invertebrates, and Fish in Chinese Surface Waters.

Nickel (Ni) is used primarily in the production of alloys like stainless steel and is increasingly being used in the production of batteries for the electric vehicle market. Exposure of Ni to ecosystems is of concern because Ni can be toxic to aquatic organisms. The influence of water chemistry constituents (e.g., hardness, pH, dissolved organic carbon) on the toxicity of Ni has prompted the development and use of bioavailability models, such as biotic ligand models (BLMs), which have been demonstrated to accurately predict Ni toxicity in broadly different ecosystems, including Europe, North America, and Australia. China, a leading producer of Ni, is considering bioavailability-based approaches for regulating Ni emissions. Adoption of bioavailability-based approaches in China requires information to demonstrate the validity of bioavailability models for the local water chemistry conditions. The present study investigates the toxicity of Ni to three standard test species (Daphnia magna, Pseudokirchneriella subcapitata, and Danio rerio) in field-collected natural waters that are broadly representative of the range of water chemistries and bioavailabilities encountered in Chinese lakes and rivers. All experimental data are within a factor of 3 of the BLM predicted values for all tests with all species. For D. magna, six of seven waters were predicted within a factor of 2 of the experimental result. Comparison of experimental data against BLM predictions shows that the existing Ni bioavailability models are able to explain the differences in toxicity that result from water chemistry conditions in China. Validation of bioavailability models to water chemistries and bioavailability ranges within China provides technical support for the derivation of site-specific Ni water quality criteria in China. Environ Toxicol Chem 2023;42:1257-1265. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Gibberellic acid mitigates nickel stress in soybean by cell wall fixation and regulating oxidative stress metabolism and glyoxalase system

It is broadly known that excessive concentration of nickel (Ni) causes venomous effects on plant health as well as food security. The underlying gibberellic acid (GA) mechanism to overcome Ni-induced stress is still unclear. Our outcomes represented the potential role of gibberellic acid (GA) to boost the soybean stress tolerance mechanism against Ni toxicity. GA elevated the seed germination, plant growth, biomass indices, and photosynthetic machinery as well as relative water contents under Ni-induced stress in soybean. We found that the GA lowered the Ni uptake, and distribution in the soybean plants, as well as GA, can decrease the Ni fixation in the root cell wall by lowering the hemicelluloses content. However, it reduces the MDA level, over-generation of ROS, electrolyte leakage, and methylglyoxal contents by up-surging the level of antioxidant enzyme, and glyoxalase I and glyoxalase II activities. Furthermore, GA regulates the antioxidant-related (CAT, SOD, APX, and GSH) and phytochelatins (PCs) genes expression to sequester the excessive Ni to the vacuoles and efflux the Ni outer the cell. Hence, less Ni was translocated toward shoots. Overall, GA augmented cell wall Ni elimination, and the antioxidant defense mechanism possibly upgraded the soybean tolerance against Ni stress.

Effects of Bio-Slurry and Chemical Fertilizer Application on Soil Properties and Food Safety of Tomato (Solanum lycopersicum Mill.)

This study evaluated the effects of bio-slurry (BS) and chemical fertilizer (CF) application on soil properties and food safety of tomato (Solanum lycopersicum Mill.). A field experiment consisting of 100% BS (5 ton BS ha−1), 100% CF (90 kg N·ha−1 + 30 kg P·ha−1 + 13 kg S·ha−1), and control was conducted. Soil samples from all the treatments were collected for their physico-chemical characteristics. The level of ten heavy metals in experimental soil and tomato fruit samples was also determined. Compared to CF and control, the application of BS improved soil physico-chemical characteristics. The BC significantly reduced the mean concentrations of Cd and Mn in the tomato fruit samples. The mean concentration of Ni (18.24 ± 0.61, 23.9 ± 0.3, and 9.66 ± 1.2 mg kg−1) and Mn (15.4 ± 2.4, 38 ± 3.3 and 21.8 ± 0.99 mg kg−1) in tomato fruit samples of BS-treated, CF-treated, and control soil, respectively, was above the safety limit set by the Food and Agriculture Organization/World Health Organization for human consumption. Similarly, the mean concentration of Cd (7.98 ± 0.72 and 3.29 ± 0.37 mg kg−1) in tomato fruit samples of CF-treated and control soil was above the safety limit. From this perspective, the consumption of these tomato fruits could be unsafe for human health with respect to Ni, Mn, and Cd toxicities. The application of BS could remediate the Cd toxicities, yet other scenarios of phytoremediation would be praiseworthy to address Ni, Cd, and Ni toxicities.

Spring wheat yield under application of growth promoting rhizobacterium in soil contaminated with nickel

Impact of growth promoting rhizobacterium Pseudomonas fluorescens 20 on the yield of spring wheat was studied in pot experiment. Plants were grown up to maturity when agrogray soil was contaminated with Ni as NiCl2·6H2O at a rate of 200 mg Ni/kg of soil against background of applying NPK fertilizers. After harvesting, content of nutrients N, P, K, Ca, Mg, Fe, Mn, Zn and Cu in grain, straw and roots was determined. N was determined by phenol technique. Resistance of plants to Ni toxicity was found under bacterial inoculation. Application of bacterium eliminated phytotoxicity of heavy metal and provided the same biomass production including grain as in control - in non-inoculated plants non-exposed Ni stress. Resistance of plants inoculated with bacterium to Ni toxicity was due to enhanced growth of root system and increase in content and accumulation of Ni in roots and, as a result this was not accompanied by increase in metal incorporation into aboveground organs. Resistance of plants inoculated with bacterium to Ni toxicity was due to enhanced growth of root system and increase in content and accumulation of Ni in roots. Application of bacterium also improved mineral nutrition of plants - increased nutrient uptake from contaminated soil. Increase in nutrient uptake by yield from contaminated soil as influenced by inoculation with bacterium was due to growth promotion and increase of plant weight in general without significant changes in content of most elements in aboveground organs and roots. Bacterium enhanced phytoextraction of heavy metal (soil cleaning) - increased Ni uptake by aboveground organs without significant changes in its content in grain and straw. Increase in Ni uptake by bacterially inoculated plants occurred without changes of soil medium reaction and was probably due to production of bacterial siderophores.

Transcriptomic, osmoregulatory and translocation changes modulates Ni toxicity in Theobroma cacao

Nickel is one of the most released trace elements in the environment and in the case of bioaccumulation in foods and beverages derived from cocoa beans can cause risk to human health. It is very important to understand how plants respond to toxic metals and which are the defense strategies they adopt to mitigate their effects. In the present study we used young plants of T. cacao, submitted to increasing Ni doses (0, 100, 200, 300, 400 and 500 mg Ni kg−1 soil) and evaluated them for a period of 30 days. Doses of Ni, from 300 mg of Ni kg−1 onwards in the soil, promoted changes in photosynthetic, antioxidant, osmoregulatory, transcriptomic and translocation levels, evidenced by the increase in the activity of antioxidant enzymes, proline, glycine betaine, upregulation of the metallothionein 2B gene (Mt2b), and lipid peroxidation of the cell membranes. Foliar gas exchange was severely affected at higher doses of Ni. In addition, reduced levels of stomatal conductivity and transpiration rate were observed from 300 mg Ni kg−1 dose onwards in the soil, which consequently affected CO2 assimilation. Phytostabilization and exclusion mechanisms control the translocation of Ni from the root to the shoot and reduce harmful effects on plant metabolism. Our results highlighted the toxicity of Ni, a trace element often underestimated in T. cacao. In particular, it was noted that doses of 100 and 200 Ni kg−1 soil, although high, do not induce toxicity in T. cacao plants. But Ni toxicity is observed from 300 mg Ni kg−1 soil onwards. This study contributed to the understanding of the harmful effects of higher doses of Ni in cacao plants and the biochemical processes the plant uses to mitigate the effects of this metal.