Nickel; whether toxic or essential for plants and environment - A review

Tidal control of heavy metal loading in the nearshore of the northwestern Indian coast

Heavy metals accumulate in the marine food chain and their excessive amounts are hazardous to aquatic and human lives. The current study presents the role of ecosystem variables especially tides in deciding the presence of ten heavy metals (Fe, Zn, Cu, Co, Cr, Mn, Ni, V, Pb, and Cd) in seawater and copepods along the Indian west coast. The Indian northwestern coast is an industrial hub, where thousands of industries release enormous volumes of effluents, while the southwest coast has a far lower number of industries. Multiple surface seawater and zooplankton samples from eight selected marine outfall regions in the nearshore of the Indian west coast showed that Fe/Cd was generally the highest/lowest in seawater (av. 184 ± 12.40 μg L-1/ av. 0.01 ± 0.01 μg L-1) and copepods (av. 41,818 ± 2867 μg. g-1/ av. 0.2 ± 0.02 μg g-1). The heavy metals in seawater/copepods generally showed the order Fe/Fe > Zn/Zn > V/Mn > Cr/Cr > Pb/Cu > Ni/Ni > Cu/Pb > Mn/V > Co/Co > Cd/Cd. Contrary to expectations, despite being loaded with massive amounts of effluent from thousands of industries, most heavy metals in seawater on the northwestern Indian coast were not higher than on the southwestern coast. It is shown here that this feature is the result of the macro-tidal nature of the northwest Indian coast (av. 7 m tide), where tidal currents, sediment resuspension, and flushing are far more intense than in the southwest (av. 1 m tide), which reduce pollution levels. Yet, the marine pollution index and bioaccumulation factor of heavy metals in copepods was found highest along the northwestern Indian coast, which are important indicators to be considered when developing environmental management strategies for the area.

Unveiling Novel Genetic Loci and Superior Alleles for Nickel Accumulation in Wheat via Genome-Wide Association Study

Nickel (Ni) pollution poses significant threats to human health and crop development through the food chain. This study aimed to identify the novel genomic regions and superior alleles associated with Ni accumulation in wheat (Triticum aestivum L.) grains using genome-wide association analysis (GWAS) with a diversity panel of 207 bread wheat varieties. In total, five unique genetic loci associated with Ni accumulation were identified and they explained, on average, 8.20-11.29% of the phenotypic variation. Among them, three unique genetic loci were mutually verified by different statistical models in at least two environments, indicating their stability across different environments. Moreover, the highest effect quantitative trait nucleotide (QTN) AX-111126872 with a quantitative trait locus (QTL) hotspot on chromosome 6B identified in this study was not reported previously. Three putative candidate genes linked to Ni accumulation were revealed from the stable genetic loci. Among them, one gene associated with the stable genetic locus on chromosome 6B (AX-111126872) encodes the glycine-rich proteins (GRPs) as a critical factor influencing Ni accumulation in wheat grains. This study increases our understanding of the genetic architecture of Ni accumulation in wheat grains, which is potentially helpful for breeding wheat varieties without Ni toxicity.

Biochar-mediated remediation of nickel and copper improved nutrient availability and physiological performance of dill plants

The presence of heavy metals, such as copper and nickel, in the rhizosphere reduces the physiological efficiency and growth of plants. This study evaluated the effects of plum tree biochar levels (0, 15, 30, and 45 g kg-1 soil) with and without copper sulfate (200 mg kg-1 soil), nickel sulfate (400 mg kg-1 soil), and their combination on dill plants in a factorial experiment with a randomized complete block design in three replicates. The results indicated that the presence of copper and nickel in the soil had detrimental effects on the growth and physiological performance of dill. Specifically, copper stress alone reduced biomass by 31%, nickel stress by 27%, and their combined treatment by 37.7%. On the other hand, incorporating biochar into the soil decreased the uptake of heavy metals, oxidative stress, and the production of osmotic regulators in the plants, while enhanced nutrient uptake (N, K, Ca, Mg, Fe, and Zn), photosynthetic pigments, and plant biomass. Increasing biochar application rate in the soil did not have any additional beneficial effect on growth and physiological characteristics of plants. These results suggest that the low rate of biochar (15 g kg-1) from agricultural wastes is an appropriate soil amendment to remediate copper and nickel pollutants in the rhizosphere to enhance nutrient availability and plant performance. Future research could focus on the long-term efficacy of biochar under diverse field conditions, soil types, and plant species to optimize sustainable agricultural practices.

Global soil pollution by toxic metals threatens agriculture and human health

Toxic metal pollution is ubiquitous in soils, yet its worldwide distribution is unknown. We analyzed a global database of soil pollution by arsenic, cadmium, cobalt, chromium, copper, nickel, and lead at 796,084 sampling points from 1493 regional studies and used machine learning techniques to map areas with exceedance of agricultural and human health thresholds. We reveal a previously unrecognized high-risk, metal-enriched zone in low-latitude Eurasia, which is attributed to influential climatic, topographic, and anthropogenic conditions. This feature can be regarded as a signpost for the Anthropocene era. We show that 14 to 17% of cropland is affected by toxic metal pollution globally and estimate that between 0.9 and 1.4 billion people live in regions of heightened public health and ecological risks.

Starvation from within: How heavy metals compete with essential nutrients, disrupt metabolism, and impair plant growth

Nutrient starvation is a critical consequence of heavy metal toxicity, severely impacting plant health and productivity. This issue arises from various sources, including industrial activities, mining, agricultural practices, and natural processes, leading to the accumulation of metals such as aluminum (Al), arsenic (As), cadmium (Cd), chromium (Cr), lead (Pb), mercury (Hg), and nickel (Ni) in soil and water. Heavy metal exposure disrupts key physiological processes, particularly nutrient uptake and transport, resulting in nutrient imbalances within the plant. Essential nutrients are often unavailable or improperly absorbed due to metal chelation and interference with transporter functions, exacerbating nutrient deficiencies. This nutrient starvation, coupled with oxidative stress induced by heavy metals, manifests in impaired photosynthesis, stunted growth, and reduced crop yields. This review presents important insights into the molecular mechanisms driving nutrient deprivation in plants exposed to heavy metals, emphasizing the roles of transporters, transcription factors, and signaling pathways. It also examines the physiological and biochemical effects, such as chlorosis, necrosis, and altered metabolic activities. Lastly, we explore strategies to mitigate heavy metal-induced nutrient starvation, including phytoremediation, soil amendments, genetic approaches, and microbial interventions, offering insights for enhancing plant resilience in contaminated soils.

The resistance of biohumus microbiome to cobalt and nickel compounds

Heavy metals, particularly cobalt and nickel, are highly toxic and widely distributed in ecosystems. Sometimes, their concentration in natural ecosystems can increase sharply due to anthropogenic activities. Metal-resistant microorganisms are considered to be promising for their detoxification. The purpose of the work was to study the sustainability of microorganisms derived from the biohumus in the presence of toxic cobalt and nickel compounds as well as determine the maximum limit concentration of Co2+ and Ni2+ for them. The biohumus served as a model natural ecosystem free from heavy metals where microorganisms were not adapted to them. The resistance of microorganisms was determined by cultivation in the medium with a gradient of simultaneous Co2+ and Ni2+ from 0 to 1000 mg/L. The quantification of Co2+ and Ni2+-resistant microorganisms in the biohumus was determined by counting the number of colony forming units on nutrient agar. Using a Niton XL5 Plus manual XRF analyzer, it was determined that in metal missile fragments the concentration of cobalt ranged from 73 ± 22 to 589 ± 34 mg/kg, the concentration of nickel was 110 ± 15-577 ± 21 mg/kg. Cobalt was not detected in all soil samples. Nickel compounds were detected in two samples of the affected soil up to 408 ± 8 mg/kg and 36 ± 4 mg/kg in soil without shell explosions. On the example of the microorganisms of the biohumus, we confirmed that natural ecosystems contain microorganisms resistant to toxic Co2+ and Ni2+ compounds in high concentrations. The concentrations of simultaneous Co2+ and Ni2+ of 100 and 200 mg/L were established not to affect the growth of microorganisms, and the number of CFUs was (6.2 ± 0.2)×105 and (6.1 ± 0.2)×105 CFU/g. The maximum permissible concentration of simultaneous Co2+ and Ni2+ for the biohumus microbiome was 700 mg/L and the number of CFUs was (5.0 ± 0.1)×102 CFU/g after a month of cultivation. Moreover, microorganisms can adapt and maintain sustainable growth even after the increase in the concentration of metals from 500 to 2500 mg/L as well as to provide the detoxification of divalent metals by transforming into insoluble non-toxic sulfides.

Dendrochemical analysis of heavy metals in Magnolia champaca tree rings in Mizoram, Northeast India

Heavy metals are among the important environmental pollutants, yet their impact in remote areas remains underexplored because of limited studies on their monitoring. This study presents the first dendrochemical analysis from Mizoram, using Magnolia champaca tree rings to assess heavy metal concentration trends at a natural forest site (Site-I) and a roadside plantation (Site-II) for about two and half decades (from 1993 to 2019). The concentrations of Zn, Pb, Fe, Cu, Ni, and Mn were analyzed in tree rings to reconstruct pollution history. The results revealed a significant difference between the two sites, with roadside tree cores exhibiting greater variability and steadily increasing heavy metal concentrations as compared to natural forest. The mean concentrations of metals in natural forest samples were in the order: Fe (18.22 mg kg⁻1) > Mn (12.01 mg kg⁻1) > Ni (7.23 mg kg⁻1) > Cu (3.71 mg kg⁻1) > Pb (0.398 mg kg⁻1) > Zn (0.411 mg kg⁻1). In contrast, roadside samples showed considerably higher metal concentrations in the order: Mn (39.92 mg kg⁻1) > Fe (22.9 mg kg⁻1) > Ni (11.61 mg kg⁻1) > Cu (10.28 mg kg⁻1) > Zn (6.723 mg kg⁻1) > Pb (3.17 mg kg⁻1). Notably, M. champaca samples collected from the roadside contained elevated levels of Pb, Fe, Cu, and Ni, exceeding the permissible limits for plant parts as prescribed by the WHO. The study underscores the potential of species as a bioindicator of heavy metal pollution. These findings are crucial for informing soil management, pollution control, and understanding nutrient-metal cycling in trees. Further research is needed to explore the plant-soil interactions and behaviours of heavy metals in these environments.

L-histidine makes Ni2+ 'visible' for plant signalling systems: Shading the light on Ni2+-induced Ca2+ and redox signalling in plants

Nickel is both an important nutrient and an ecotoxicant for plants. Organic ligands, such as L-histidine (His), play a key role in Ni2+ detoxification. Here, we show that His (added together with 0.01-10 mM Ni2+) decreases Ni2+ toxicity to Arabidopsis thaliana roots not only as a result of a decrease in Ni2+ activity, but also via the induction of signalling phenomena important for adaptation such as the generation of reactive oxygen species (ROS) and cytosolic Ca2+ transients. With the use of EPR spectroscopy, we demonstrate that Ni-His complexes generate hydroxyl radicals that is not detected by the addition of Ni2+ or His separately. Similarly, Ni-His complexes, but not Ni2+, activate Ca2+ influx and K+ efflux currents in patch-clamped root protoplasts resulting in distinct cytosolic Ca2+ signals and a transient K+ release. His prevented programmed cell death symptoms (cytoplasm shrinkage, protease and endonuclease activation) induced by Ni2+ and inhibited Ni2+ accumulation at [Ni2+]>0.3 mM. Intriguingly, priming of roots with Ni-His stimulated plant resistance to Ni2+. Overall, these data show that His triggers ROS-Ca2+-mediated reactions making Ni2+ 'visible' for plant signalling machinery and facilitating adaptation to the excess Ni2+.

Impact of Nutrient Stress on Plant Disease Resistance

Plants are constantly exposed to abiotic and biotic stresses that seriously affect crop yield and quality. A coordinated regulation of plant responses to combined abiotic/biotic stresses requires crosstalk between signaling pathways initiated by each stressor. Interconnected signaling pathways further finetune plant stress responses and allow the plant to respond to such stresses effectively. The plant nutritional status might influence disease resistance by strengthening or weakening plant immune responses, as well as through modulation of the pathogenicity program in the pathogen. Here, we discuss advances in our understanding of interactions between nutrient stress, deficiency or excess, and immune signaling pathways in the context of current agricultural practices. The introduction of chemical fertilizers and pesticides was a major component of the Green Revolution initiated in the 1960s that greatly boosted crop production. However, the massive application of agrochemicals also has adverse consequences on the environment and animal/human health. Therefore, an in-depth understanding of the connections between stress caused by overfertilization (or low bioavailability of nutrients) and immune responses is a timely and novel field of research with important implications for disease control in crop species. Optimizing nutrient management practices tailored to specific environmental conditions will be crucial in maximizing crop production using environmentally friendly systems.

Evaluation of the dynamics of nutrients and potentially toxic elements along a major river in Ethiopia using multivariate statistical techniques: Implications of possible co-occurrences

This study utilized established field and laboratory methods and multivariate statistical tools to evaluate the nutrient and potentially toxic elements (PTEs) distribution, identify possible sources, and determine potential co-existence in the Awash River. The levels of soluble reactive phosphorus (SRP), total phosphorus (TP), NO3-N, Mn, Ni, Cr, and Cu generally increased downstream in the upper Awash, with the highest respective values of 0.70, 1.34, 1.19, 1.58, 1.03, 0.85, and 0.11 mg L-1 at the inlet to Lake Koka. Sites found downstream of the inflow of Lake Beseka and Metehara town showed the highest levels of Fe, B, Zn, and dissolved silica. Principal components and correlation analysis findings revealed strong associations (r ≥ 0.80, p < 0.05) between nutrient parameters (SRP, TP, and NO3-N) and PTEs (Cu, Ni, Mn, and Cr), implying common origins and potential co-occurrences. The potential co-occurrences of these parameters may strengthen their potential individual impacts due to complex interactions.

Nickel-induced multimetal uptake in two microalgal species (Chlorella sorokiniana and Chlamydomonas reinhardtii) and its effect on growth and lipid unsaturation

As the concern for Ni contamination in the aquatic environment escalates, efforts for microalgal use in environmental monitoring and bioremediation are increasing. This study aims to evaluate the potential of Chlorella sorokiniana and Chlamydomonas reinhardtii for Ni bioremediation by investigating their physiological stress responses in Ni-contaminated environments. The analysis focuses on how Ni(II) uptake affects cell growth, nutrient metal homeostasis, and lipid unsaturation levels, as these parameters are critical indicators of metabolic stability and resilience essential for effective bioremediation. The microalgae were grown under mixotrophic conditions in a tris-acetate-phosphate (TAP) medium enriched with Ni(II), at concentrations (1-6 mg∙L-1) exceeding those typically found in wastewater, providing insights into metal stress under severe contamination conditions. Even though increased uptake of Ni(II) was observed for both algal species, accompanied by growth suppression at high Ni(II) concentrations, multi-elemental trace analysis revealed a significant, Ni concentration-dependent, uptake of growth media essential metals as well. Specifically, for both algal species, Zn uptake concentrations increased by approximately 20 times when going from control cultures, with no Ni(II) added, to cultures incubated with increasing Ni(II) concentrations. Overall, Zn uptake was determined to be approximately 3 orders of magnitude higher than Ni(II) uptake when high concentrations of Ni(II) were present, making Zn the metal with the most significant uptake. Similar uptake trends were observed for Cu and Co for both algal species, with Cu uptake being approximately 2 orders of magnitude higher, while Co remained below the Ni(II) concentrations at high added Ni(II) concentrations. For Chlorella sorokiniana, increased Fe uptake relative to Ni(II) uptake was observed (2 orders of magnitude higher), as was the case for Mn (1 order of magnitude higher). This induced increase in uptake of some of the growth media metals was attributed to their liberation from ethylenediaminetetraacetic acid (EDTA) in tris-acetate-phosphate (TAP) medium, following the addition of Ni(II), which has a higher stability constant (Kf) with EDTA and was added at concentrations comparable or higher than those of the other metals. Calculated levels of free Ni(II) and free metals in the medium matched the observed metal uptake trends as determined using multielemental inductively coupled plasma mass spectrometry. Negative ion electrospray mass spectrometry also revealed that EDTA-metal complexes in the TAP media decreased as Ni(II) concentrations increased. The lipid unsaturation level and relative ω-3 fatty acids concentration of both microalgal species, based on 1H Nuclear Magnetic Resonance analysis, decreased with increasing Ni(II) concentration, with the decrease being more pronounced at Ni(II) incubation concentrations of 4 and 6 ppm. Unsaturation levels for individual lipid classes [monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), and sulfoquinovosyldiacylglycerol (SQDG)] in Chlamydomonas reinhardtii cells were also studied using positive ion mode electrospray mass spectrometry. At the highest Ni(II) concentrations, an overall reduction in unsaturation levels was observed for all 3 lipid classes, indicating a significant impact of elevated metal ion concentrations on membrane fluidity and therefore on cellular physiology and metabolism. Comparison of the two microalgal species under Ni-enriched conditions shows that Chlorella sorokiniana exhibits greater tolerance to the metal-induced stress under study than Chlamydomonas reinhardtii, suggesting its higher efficiency for the bioremediation in Ni-contaminated environments.

Phenolics Profile and Phenol-Related Enzyme Activities in Cucumber Plants Under Ni Stress

Ni phytotoxicity has been attributed to its multidirectional detrimental effects on plant cell structure and function. However, relatively little is known about Ni's impact on phenolic metabolism in plants. The objective of our study was to obtain insight into the effect of Ni treatment on phenolic compound composition, phenol-related enzyme activities, and lignin accumulation in cucumber plants. Besides growth reduction, the chlorophyll a and carotenoid contents as well as the chlorophyll a fluorescence parameters, namely, the maximum photochemical efficiency of PS II and non-photochemical quenching, were significantly decreased in the Ni-treated cucumber plants. Application of Ni resulted in changes in the phenolic acid and flavonoid profiles; however, the total content of the detected phenolic compounds remained unchanged in the leaf and slightly decreased in the root. The Ni-induced release of free phenolic acids from their conjugates was found in the leaf. Ni treatment led to a marked increase in leaf peroxidase activities assayed with various phenolic substrates, while it did not influence phenyl ammonia lyase and polyphenol oxidase activities. Increased lignin deposition was observed in the leaf blade of Ni-exposed plants. Neither lignin accumulation nor induction of peroxidase activities were found in the root. Our results indicate that the Ni effect on phenolic compound composition and related enzyme activities is organ-specific. The observed changes in the content of individual compounds might result rather from the metal-triggered conversions of the compounds constitutively present in the cucumber tissues than from de novo synthesis.

Evaluating and modeling the efficacy of Stipagrostis plumosa for the phytoremediation of petroleum compounds in crude oil-contaminated soil

This study focused on using Stipagrostis plumosa for phytoremediation to eliminate total petroleum hydrocarbons (TPHs) and heavy metals (HMs) like cadmium (Cd), chromium (Cr), lead (Pb), and nickel (Ni) from oil-contaminated soil. Conducted over six months at a field-scale without artificial pollutants, soil samples were analyzed using gas chromatography‒mass spectrometry (GC‒MS) for TPHs and inductively coupled plasma-optical emission spectroscopy (ICP‒OES) for HMs. Results after six months revealed that plots with plants had significantly higher average removal percentages for TPHs (61.45%), Cd (39.4%), Cr (46.1%), Pb (41.5%), and Ni (44.2%) compared to the control group (p <0.05). Increased microbial respiration and bacteria populations in planted plots indicated enhanced soil microbial growth. Kinetic rate models aligned well with the first-order kinetic rate model for all pollutants (R2 >0.9). Overall, the study demonstrates that S. plumosa can effectively reduce TPHs and HMs in oil-contaminated soil, making it a promising option for pollutant absorption.

Transcriptome response in a marine copepod under multigenerational exposure to ocean warming and Ni at an environmentally realistic concentration

Due to anthropogenic activities, coastal areas have been challenged with multi-stresses such as ocean warming and nickel (Ni) pollution. Currently, studies have concerned the combined effects of Ni and warming in marine organisms at the phenotypic level; however, the underlying molecular mechanisms are poorly known. In this study, a marine copepod Tigriopus japonicus was maintained under warming (+ 4℃) and an environmentally realistic level of Ni (20 μg/L) alone or combined for three generations (F0-F2). Transcriptome analysis was performed for the F2 individuals. We found that the gene transcripts of copepods were predominantly down-regulated after Ni and warming exposure. Based on the results of GO and KEGG analysis, chitin metabolism, detoxification, antioxidant, apoptosis, and energy metabolism were screened in this study. Among the above functions, the combined exposure enriched more differential expression genes and had a larger fold change compared to Ni exposure alone, suggesting that warming increased the negative effect of Ni on marine copepods from a molecular perspective. Specifically, the combined exposure exacerbated the down-regulation of defense, apoptosis, xenobiotic efflux, GSH system, and energy metabolism, as well as the up-regulation of detoxification and peroxidase system. Overall, this study indicates that both ocean warming and Ni pollution adversely affect the marine copepod T. japonicus from multigenerational transcriptome analysis, especially warming increased Ni toxicity to marine copepods, and our results also provide references to the mechanism concerning the effects of Ni and warming on marine copepods.

Improving Ni2+ Tolerance of Arabidopsis by Overexpressing Bacterial rcnA Gene Encoding a Membrane-Bound Exporter of Ni2

The prerequisite for breeding a plant to be used in phytoremediation is its high tolerance to grow normally in soil contaminated by certain heavy metals. As mechanisms of plant uptake and transport of nickel (Ni) are not fully understood, it is of significance to utilize exogenous genes for improving plant Ni tolerance. In this study, rcnA from Escherichia coli encoding an exporter of Ni and cobalt was overexpressed constitutively in Arabidopsis thaliana, and the performance of transgenic plants was assayed under Ni stress. The subcellular localization of rcnA in plant cells was found to be the plasma membrane. Constitutive overexpression of rcnA in Arabidopsis rendered better growth of either seedlings on agar medium containing 85, 100, and 120 μM NiCl2 or adult plants in a nutrient solution with 5 mM NiCl2 added. Compared to the wildtype, rcnA-OE transgenic plants under Ni stress accumulated lower levels of reactive oxygen species (i.e., superoxide and hydrogen peroxide) in leaves and exhibited less oxidative damage in shoots, as demonstrated by less electrolyte leakage and the lower malondialdehyde content. Notably, rcnA-OE transgenic plants retained a higher content of Ni in roots and had a lower content of Ni in shoots. Therefore, our findings indicated that the bacterial rcnA gene may be utilized to improve plant Ni tolerance through genetic transformation.

Integrating environmental, ecological and human health risk assessments for heavy metals in tropical ultramafic soils

Ultramafic soils are a natural source of metals such as Ni, Co and Cr that can pose ecosystem and human risks. Here, we assessed the environmental, ecological, and human health (carcinogenic and non-carcinogenic) risks from exposure to ultramafic soils through an integrated approach using petrographic and soil mineralogical assessments together with total, available, bioaccessible, and soil fractions analyses of Ni, Co and Cr in ultramafic soils from Brazil. The metal concentrations were similar or up to 5-fold higher for Ni than other studies worldwide in ultramafic soils. Soil sequential extraction showed Co and Ni predominantly bound to Fe and Mn oxides, while Cr was mostly in residual fractions. Medium environmental risks were found for Ni (RAC = 13.0), but no environmental risks were associated with Co and Cr in soils. Ecological risks were high (PERI = 522.8) and significantly high (PERI = 1759.9). Low metal bioaccessibility led to acceptable carcinogenic and non-carcinogenic risks for all routes of human exposure to soil, but consuming vegetables grown in these soils posed unacceptable cancer risks (> 10-3). Our results reinforce the need to monitor ultramafic areas regarding the mobility and availability of metals in the soil to ensure food safety and human health.

Spatial distribution and impacts of microplastics on potato growth and yield in agroecosystems in Sialkot, Pakistan

Microplastic (MP) pollution is a growing concern, yet its impacts on agroecosystems remain poorly understood. This study investigates MP contamination in the agroecosystems of Sialkot, Pakistan, and its potential effects on the growth, physio-biochemical attributes, and yield of potato (Solanum tuberosum L.). Plant and soil samples from 10 diverse agricultural fields were collected and analyzed for MP contamination. FTIR analysis revealed widespread MP presence in the soil across all sites. Fragment, film, and fiber types dominated, with low-density polyethylene (22.42 %), high-density polyethylene (18.05 %), and polystyrene (12.3 %) being the most prevalent polymers. A significant variation in plant growth parameters was observed. The number of tubers per plant also exhibited a significant difference, as evidenced by the decline in potato yield with increasing levels of MP contamination. Potato yield showed a negative correlation with MP contamination levels. The nutrients (Zn, Cu, Ni, and Na) uptake in plant shoots was also observed to be decreased except for Mg and Mn at all sites. This study showed that MPs are contaminating our agricultural lands and they may affect growth and yield of potato. Additional research is needed to understand the underlying mechanisms and develop mitigation strategies to improve agricultural productivity and food security.

Beneficial or detrimental? How nickel application alters the ionome of soybean plants

The use of nickel (Ni) in agriculture may represent one of the most significant cases of plant hormesis ever reported, as plants exhibit both positive and negative responses depending on the level of exposure to this element. For a more comprehensive understanding of this effect, the next step is to conduct studies on the dynamics of pre-existing chemical elements in the system (ionomic profile), especially when introducing Ni as a novel nutrient for the plants. This micronutrient is of particular interest to the fertilization of leguminous plants, such as the soybean, due to its additional effects on the biological nitrogen fixation process. This study thus evaluated the influence of five doses of Ni (0.0, 0.5, 1.0, 3.0, and 9.0 mg of Ni kg-1) on the ionomic profile of soybean genotypes using modern quantification techniques. The results revealed that the addition of Ni reduced the concentration of cationic micronutrients manganese (Mn), iron (Fe), zinc (Zn), and copper (Cu), while it increased the concentration of macronutrients nitrogen (N) and magnesium (Mg). The application of Ni also resulted in a reduction of the potentially toxic element aluminum (Al). Correlations were also observed for these elements, indicating that Ni could be a controlling agent in elemental absorption and translocation. The ionome of the leaf tissues exhibited the most significant alterations, followed by the grains, nodules, and roots. Exogenous agronomic doses of Ni proved beneficial for the growth and production of soybean plants, although a genotypic effect was observed. The treatment with 9.0 mg of Ni kg-1, resulted in a new ionomic profile related to toxicity, demonstrating suboptimal plant development. Thus, the application of Ni in appropriate doses had a significant impact on the ionomic profile of soybeans, improving plant development and implying resistance to potentially toxic elements such as Al.

Silicon might mitigate nickel toxicity in maize roots via chelation, detoxification, and membrane transport

Nickel is an essential micronutrient for plant growth and development. However, in excessive amounts caused by accidental pollution of soils, this heavy metal is toxic to plants. Although silicon is a non-essential nutrient, it accumulates in most monocots, particularly the vital crop maize (corn, Zea mays). In fact, this metalloid mineral can alleviate the toxicity of heavy metals, though the mechanism is not entirely clear yet. Herein, we measured proteome, gene expression, enzyme activities, and selected sugars to investigate such effect thoroughly. Deep proteomic analysis revealed a minor impact of 100 µM Ni, 2.5 mM Si, or their combination on roots in 12-day-old hydroponically grown maize seedlings upon 9 days of exposure. Nonetheless, we suggested plausible mechanisms of Si mitigation of excessive Ni: Chelation by metallothioneins and phytochelatins, detoxification by glycine betaine pathway, and restructuring of plasma membrane transporters. Higher activity of glutathione S-transferase confirmed its plausible involvement in reducing Ni toxicity in combined treatment. Accumulation of sucrose synthase and corresponding soluble sugars in Ni and combined treatment implied high energy requirements both during heavy metal stress and its mitigation. Expression analysis of genes coding a few differentially accumulated proteins failed to reveal concordant changes, indicating posttranscriptional regulation. Proposed mitigation mechanisms should be functionally validated in follow-up studies.

Dissolution and solubility of the calcium-nickel carbonate solid solutions [(Ca1-xNix)CO3] at 25 °C

A series of the calcium-nickel carbonate solid solutions [(Ca1-xNix)CO3] were synthesized and their dissolution in N2-degassed water (NDW) and CO2-saturated water (CSW) at 25 °C was experimentally investigated. During dissolution of the synthetic solids (Ni-bearing calcite, amorphous Ca-bearing NiCO3 and their mixtures), the Ni-calcite and the Ca-NiCO3 dissolved first followed by the formation of the Ni-bearing aragonite-structure phases. After 240-300 days of dissolution in NDW, the water solutions achieved the stable Ca and Ni concentrations of 0.592-0.665 and 0.073-0.290 mmol/L for the solids with lower Ni/(Ca + Ni) mol ratios (XNi), or 0.608-0.721 and 0.273-0.430 mmol/L for the solids with higher XNi, respectively. After 240-300 days of dissolution in CSW, the water solutions achieved the stable Ca and Ni concentrations of 1.094-3.738 and 0.831-4.300 mmol/L, respectively. For dissolution in NDW and CSW, the mean values of log IAP (Ion activity products) in the final stable state (≈ log Ksp, Solubility product constants) were determined to be - 8.65 ± 0.04 and - 8.16 ± 0.11 for calcite [CaCO3], respectively; - 8.50 ± 0.02 and - 7.69 ± 0.03 for the synthetical nickel carbonates [NiCO3], respectively. In respect to the bulk composition of the (Ca1-xNix)CO3 solid solutions, the final log IAP showed the highest value when XNi = 0.10-0.30. Mostly, the mean values of log IAP increased with the increasing XNi in respect to the Ni-calcite, the Ni-aragonite and the amorphous Ca-Ni carbonate. The plotting of the experimental data on the Lippmann diagram for the (Ca1-xNix)CO3 solid solution using the predicted Guggenheim parameters of a0 = 2.14 and a1 = - 0.128 from a miscibility gap of XNi = 0.238 to 0.690 indicated that the solids dissolved incongruently and the final Ca and Ni concentrations in the water solutions were simultaneously limited by the minimum stoichiometric saturation curves for the Ni-calcite, Ni-aragonite and the amorphous Ca-Ni carbonate. During dissolution in NDW, the Ni2+ preferred to dissolve into the water solution and Ca2+ preferred to remain in the solid, while during dissolution in CSW for the solids with higher XNi, the Ca2+ preferred to dissolve into the water solution and Ni2+ preferred to remain in the solid. These findings provide valuable insights into understanding the mechanisms governing Ni geochemical cycle in natural environments.

The Role of Metal Tolerance Proteins (MTPs) Associated with the Homeostasis of Divalent Mineral Elements in Ga-Treated Rice Plants

Mineral elements typically act as transported substrates for metal tolerance proteins (MTPs). The chelation of MTPs with heavy metal ions is a suggestive detoxification pathway in plants; therefore, the trade-off between transporting mineral elements and chelating excess toxic metal ions is inevitable. Gallium (Ga) is an emerging pollutant associated with high-tech industries. This study investigated the impact of Ga stress on MTPs, subsequently altering the transport and distribution of mineral elements. Gallium exposure reduced rice seedling biomass, with roots accumulating more Ga than shoots. Ga stress also changed the rice plants' subcellular mineral element distribution. PCR assays showed that Ga stress negatively affected all genes belonging to the Mn group, except OsMTP9. While Mn accumulation in the rice cellular compartments did not respond positively to Ga stress, OsMTP8, OsMTP8.1, OsMTP11, and OsMTP11.1 were found to be intimately connected to Mn transport and repressed by increased Ga accumulation in roots. Mg and Cu accumulated in the cytosol and organelles of Ga-treated rice plants, while OsMTP9 expression increased, demonstrating its importance in transporting Mg and Cu. A positive link between Ga stress and Zn accumulation in the cytosol and organelles was found, and OsMTP7 and OsMTP12 expression was positive, suggesting that Ga stress did not impair their Zn transport. Notably, Ga exposure down-regulated Fe-transporting OsMTP1 and OsMTP6, wherein the subcellular concentrations of Fe showed negative responses to Ga accumulation. These findings provide valuable insights into elucidating the roles of OsMTPs in Ga tolerance and the transport of these mineral elements.

Methodological insights into soil elemental nickel in typical Karst areas: comprehensive analysis of geochemical characteristics, source determination, and influencing factors

Excessive levels of Nickel in the soil can compromise the security of agricultural products, posing a threat to health of human beings; therefore, the repair and treatment of Nickel exceeding the standard levels in soil are particularly critical. Although it is crucial that the potential restoration of Nickel in ensuring the security of both soil and farm produce within karst regions., few studies have been conducted on the potential restoration of large-scale Nickel-contaminated soils. In this study, the soil in Wuming, Guangxi, a typical karst area, was comprehensively studied. 12,547 surface soil samples, 134 deep soil samples and 60 soil profiles were collected systematically. The results showed that the Nickel background value of the surface soil was 34.9 mg/kg, indicating strong background characteristics and high variability. Principal component analysis showed that soil Nickel was primarily derived from natural sources in the geological background and partly derived from agricultural sources. Analysis of variance showed that the Nickel content of the soil was affected by the parent rock, soil type, soil use type, and topography. In addition, the distribution of Nickel in the soil profile increased exponentially with depth. Therefore, the exponential model and multiple integrals were used to derive the formula for the Nickel potential restoration amount at different depth ranges, and the potential restoration amount of soil Nickel was calculated based on different parent material, soil, and land use types. The formula is reasonable and representative and can provide a theoretical basis for the remediation and treatment of Nickel-polluted soil in karst areas.

Assessment of selected tree species as phytoremediation agents in polluted soils

The study investigates the ability of selected tree species to absorb heavy metals (Pb, Ni, Zn) from polluted soils. Seedlings of Adansonia digitata (P1), Jatropha curcas (P2), and Hildegardia barteri (P3) were transplanted into polythene pots with soils from a dumpsite (T1), highway (T2), industrial area (T3), and farmland (T4), forming a 3x4 factorial experiment replicated five times in a Completely Randomized Block Design. Pre-sowing analysis showed T1 and T2 had the highest Pb and Zn concentrations, T3 had the highest Ni, and T4 had the lowest heavy metal concentrations. After 12 weeks, heavy metal concentrations decreased in all soils. P1 concentrated metals in the root, P2 in the shoot, and P3 in various plant parts, with significant differences between species. P2 was identified as an effective phytoextractor for Pb and Zn (TF > 1), and P3 for Ni. All species showed potential for phytostabilization. The study concludes that these species are viable options for phytoremediation of heavy metals in contaminated soils.

Toxicity and bioassimilation of lead and nickel in farm ruminants fed on diversified forage crops grown on contaminated soil

The cultivation of forage crops on wastewater-irrigated soils, while common in many developing countries, poses significant risks due to heavy metal pollution, particularly Lead (Pb) and Nickel (Ni). This practice, aimed at addressing water scarcity challenges and providing affordable irrigation, was investigated for its ecological and human health implications across three diverse sites (site A, site B, and site C). Our study unveiled increases in Pb concentrations in contaminated soil, cultivated with Sesbania bispinosa showing the highest Pb accumulation. The Ni concentrations ranged from 5.34 to 10.43 across all forage crop samples, with S. fruticosa from site C displaying the highest Ni concentration and S. bicolor from site A exhibiting the lowest. Trace element concentrations in the specimens were determined using an atomic absorption spectrophotometer. The Pb levels in the blood, hair, and feces of farm ruminants (cows, buffaloes, and sheep) varied across the sites, with buffaloes consistently displaying the highest Pb levels. Insights into daily Pb intake by ruminant's highlighted variations influenced by plant species, animal types, and sites, with site C, the cows exhibiting the highest Health Risk Index (HRI) associated with lead exposure from consuming forage crops. Soil and forage samples showed Pb concentrations ranging from 8.003 to 12.29 mg/kg and 6.69-10.52 mg/kg, respectively, emphasizing the severe health risks associated with continuous sewage usage. Variations in Ni concentrations across animal blood, hair, and feces samples underscored the importance of monitoring Ni exposure in livestock, with sheep at site B consistently showing the highest Ni levels. These findings highlight the necessity of vigilance in monitoring trace element (Pb and Ni) exposure in forage crops and livestock, to mitigate potential health risks associated with their consumption, with variations dependent on species, site, and trace element concentrations.

The Role of Low-Molecular-Weight Organic Acids in Metal Homeostasis in Plants

Low-molecular-weight organic acids (LMWOAs) are essential O-containing metal-binding ligands involved in maintaining metal homeostasis, various metabolic processes, and plant responses to biotic and abiotic stress. Malate, citrate, and oxalate play a crucial role in metal detoxification and transport throughout the plant. This review provides a comparative analysis of the accumulation of LMWOAs in excluders, which store metals mainly in roots, and hyperaccumulators, which accumulate metals mainly in shoots. Modern concepts of the mechanisms of LMWOA secretion by the roots of excluders and hyperaccumulators are summarized, and the formation of various metal complexes with LMWOAs in the vacuole and conducting tissues, playing an important role in the mechanisms of metal detoxification and transport, is discussed. Molecular mechanisms of transport of LMWOAs and their complexes with metals across cell membranes are reviewed. It is discussed whether different endogenous levels of LMWOAs in plants determine their metal tolerance. While playing an important role in maintaining metal homeostasis, LMWOAs apparently make a minor contribution to the mechanisms of metal hyperaccumulation, which is associated mainly with root exudates increasing metal bioavailability and enhanced xylem loading of LMWOAs. The studies of metal-binding compounds may also contribute to the development of approaches used in biofortification, phytoremediation, and phytomining.

Nickel tolerance is channeled through C-4 methyl sterol oxidase Erg25 in the sterol biosynthesis pathway

Nickel (Ni) is an abundant element on Earth and it can be toxic to all forms of life. Unlike our knowledge of other metals, little is known about the biochemical response to Ni overload. Previous studies in mammals have shown that Ni induces various physiological changes including redox stress, hypoxic responses, as well as cancer progression pathways. However, the primary cellular targets of nickel toxicity are unknown. Here, we used the environmental fungus Cryptococcus neoformans as a model organism to elucidate the cellular response to exogenous Ni. We discovered that Ni causes alterations in ergosterol (the fungal equivalent of mammalian cholesterol) and lipid biosynthesis, and that the Sterol Regulatory Element-Binding transcription factor Sre1 is required for Ni tolerance. Interestingly, overexpression of the C-4 methyl sterol oxidase gene ERG25, but not other genes in the ergosterol biosynthesis pathway tested, increases Ni tolerance in both the wild type and the sre1Δ mutant. Overexpression of ERG25 with mutations in the predicted binding pocket to a metal cation cofactor sensitizes Cryptococcus to nickel and abolishes its ability to rescue the Ni-induced growth defect of sre1Δ. As overexpression of a known nickel-binding protein Ure7 or Erg3 with a metal binding pocket similar to Erg25 does not impact on nickel tolerance, Erg25 does not appear to simply act as a nickel sink. Furthermore, nickel induces more profound and specific transcriptome changes in ergosterol biosynthetic genes compared to hypoxia. We conclude that Ni targets the sterol biosynthesis pathway primarily through Erg25 in fungi. Similar to the observation in C. neoformans, Ni exposure reduces sterols in human A549 lung epithelial cells, indicating that nickel toxicity on sterol biosynthesis is conserved.

GLDA exhibits advantages in the phytoextraction of Cd and Ni in land-applied municipal sludge

Landscape utilization is a green and environment-friendly way of disposing of compost sludge. Garden plants can extract heavy metals from the sludge of land use, but the effect is not enough to be widely used. Chelating agents have been found to facilitate the extraction of heavy metals from plants and are expected to be popularized if they are also environmentally friendly. In this study, the effects of methylglycinediacetic acid trisodium salt (MGDA), tetrasodium glutamate diacetate (GLDA), and ethylene diamine tetraacetate (EDTA) on the extraction of Ni and Cd from compost sludge by Symphytum officinale L. were studied through the pot experiment. Compared with the control group, the application of 5-10 mmol kg-1 MGDA and 1-9 mmol kg-1 GLDA promoted plant growth, while the application of 3-4 mmol kg-1 EDTA inhibited plant growth. The highest Ni content in shoots appeared in 4 mmol kg-1 GLDA treatment, which was 4.2 times that of the CK group. The highest shoot Cd concentration appeared in 4 mmol kg-1 EDTA treatment, 6.5 times that of CK. The promotion effects of the three reagents on the acid-extractable state of Cd were similar, while that of GLDA on the acid-extractable state of Ni was outstanding. The results of this study suggested that S. officinale could be a potential phytoextraction plant for Cd and Ni, and GLDA could friendly promote the Ni phytoextraction ability of the plant. The study provides a new and efficient method for phytoremediation of heavy metals in soil.

Genome-wide association study of trace elements in maize kernels

Maize (Zea mays L.), a staple food and significant economic crop, is enriched with riboflavin, micronutrients and other compounds that are beneficial for human health. As emphasis on the nutritional quality of crops increases maize research has expanded to focus on both yield and quality. This study exploreed the genetic factors influencing micronutrient levels in maize kernels through a comprehensive genome-wide association study (GWAS). We utilized a diverse panel of 244 inbred maize lines and approximately 3 million single nucleotide polymorphisms (SNPs) to investigate the accumulation of essential and trace elements including cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), selenium (Se) and zinc (Zn). Our analysis identified 842 quantitative trait loci (QTLs), with 12 QTLs shared across multiple elements and pinpointed 524 potential genes within a 100 kb radius of these QTLs. Notably ZmHMA3 has emerged as a key candidate gene previously reported to influence the Cd accumulation. We highlighted ten pivotal genes associated with trace element transport including those encoding heavy metal ATPases, MYB transcription factors, ABC transporters and other crucial proteins involved in metal handling. Additionally, haplotype analysis revealed that eight inbred linesaccumulated relatively high levels of beneficial elements while harmful elements were minimized. These findings elucidate the genetic mechanisms underlying trace element accumulation in maize kernels and provide a foundation for the breeding of nutritionally enhanced maize varieties.

Response patterns of the microbiome during hexavalent chromium remediation by Tagetes erecta L

Chromium pollution, particularly hexavalent chromium [Cr(VI)], may threaten the environment and human health. This study investigated the potential of Tagetes erecta L. (Aztec marigold) for phytoremediation of soil contaminated with Cr(VI), and focused on the effects of varying concentrations of Cr(VI) on both the physicochemical properties of soil and microbiome of Tagetes erecta L. We observed that Tagetes erecta L. showed tolerance to Cr(VI) stress and maintained normal growth under these conditions, as indicated by bioconcentration factors of 0.33-0.53 in shoots and 0.39-0.70 in roots. Meanwhile, the structure and diversity of bacterial communities were significantly affected by Cr(VI) pollution. Specifically, Cr(VI) had a more significant effect on the microbial community structure in the endophytic of Tagetes erecta L. than in the rhizosphere (p < 0.05). The genera Devosia and Methylobacillus were positively correlated with Cr(VI) concentrations. Biomarkers such as Bacilli and Pseudonocardia were identified under the different Cr(VI)-contaminated treatments using LEfSe. In addition, the interaction and stability of the endophytic microbiome were enhanced under Cr(VI) stress. This study explored the interactions between heavy metals, microorganisms, and plants, providing valuable insights for developing in situ bioremediation of Cr(VI)-contaminated soils.

Microbial mediated remediation of heavy metals toxicity: mechanisms and future prospects

Heavy metal pollution has become a serious concern across the globe due to their persistent nature, higher toxicity, and recalcitrance. These toxic metals threaten the stability of the environment and the health of all living beings. Heavy metals also enter the human food chain by eating contaminated foods and cause toxic effects on human health. Thus, remediation of HMs polluted soils is mandatory and it needs to be addressed at higher priority. The use of microbes is considered as a promising approach to combat the adverse impacts of HMs. Microbes aided in the restoration of deteriorated environments to their natural condition, with long-term environmental effects. Microbial remediation prevents the leaching and mobilization of HMs and they also make the extraction of HMs simple. Therefore, in this context recent technological advancement allowed to use of bioremediation as an imperative approach to remediate polluted soils. Microbes use different mechanisms including bio-sorption, bioaccumulation, bioleaching, bio-transformation, bio-volatilization and bio-mineralization to mitigate toxic the effects of HMs. Thus, keeping in the view toxic HMs here in this review explores the role of bacteria, fungi and algae in bioremediation of polluted soils. This review also discusses the various approaches that can be used to improve the efficiency of microbes to remediate HMs polluted soils. It also highlights different research gaps that must be solved in future study programs to improve bioremediation efficency.

Correlation between environmental nickel exposure and the development of arthritis: A large-sample cross-sectional investigation

BACKGROUND

Nickel is a common metallic element in orthopedic implanted devices and living environment exposures. It is associated with varieties of diseases. The purpose of this investigation was to explore the correlation between nickel exposure and the prevalence of arthritis.

METHODS

Data were obtained from the National Health and Nutrition Examination Survey (NHANES) database from 2017 to 2018. Multivariate logistic regression was utilized to analyze the relationship between urinary nickel levels and arthritis. In addition, hierarchical modeling further explored the interactions and trends between urinary nickel levels and arthritis. Propensity score matching (PSM) method was used to reduce the effect of confounders. Additionally, restricted cubic spline curve (RCS) was used to assess the possible nonlinear association between urinary nickel and arthritis.

RESULTS

The investigation was comprised of 139 arthritis patients and 547 healthy participants. After correction by PSM, there was a positive correlation between arthritis and Nickel exposure levels. The risk of developing arthritis was significantly increased when nickel exposure levels were in the Q4 interval (OR=2.25, 95 % CI=1.03-5.02). When stratified by age and sex, nickel exposure was significantly and positively associated with arthritis in the subgroup aged over 65 years. (OR=2.78,95 %CI=1.20-6.46). Also, the difference between nickel exposure and arthritis was significant in the different gender subgroups (interaction P<0.05). Restricted cubic spline (RCS) results showed a significant linear association between nickel exposure levels and arthritis. In addition, there was a non-linear association between nickel exposure and arthritis across gender and age subgroups.

CONCLUSION

A significant positive association between nickel exposure levels and arthritis was showed by the experimental data. Controlling the use of nickel-containing medical prostheses and reducing exposure to nickel-containing daily necessity could help to slow the onset of arthritis.

Colorimetric and Fluorometric N-Acylhydrazone-based Chemosensors for Detection of Single to Multiple Metal Ions: Design Strategies and Analytical Applications

The development of optical sensors for metal ions has gained significant attention due to their broad applications in biology, the environment, and medicine. Colorimetric and fluorometric detection methods are particularly valued for their simplicity, cost-effectiveness, high detection limits, and analytical power. Among various chemical probes, the hydrazone functional group stands out for its extensive study and utility, owing to its ease of synthesis and adaptability. This review provides a comprehensive overview of N-acylhydrazone-based probes, serving as highly effective colorimetric and fluorometric chemosensors for a diverse range of metal ions. Probes are categorized into single-ion, dual-ion, and multi-ion chemosensors, each further classified based on the detected metal(s). Additionally, the review discusses detection modes, detection limits, association constants, and spectroscopic measurements.

Salicylic acid and jasmonic acid-mediated different fate of nickel phytoremediation in two populations of Alyssum inflatum Nyár

This study investigates Ni phytoremediation and accumulation potential in the presence of salicylic acid (SA) (0, 50 and 200 μM) and jasmonic acid (JA) (0, 5 and 10 μM) in two populations of Alyssum inflatum under various nickel (Ni) doses (0, 100 and 400 μM). By measuring Ni levels in the shoots and roots, values of bioaccumulation coefficient (BAC), biological concentration factor (BCF) and translocation factor (TF) were calculated to quantify Ni accumulation and translocation between plant organs. Additionally, the amounts of histidine (His), citric acid (CA) and malic acid (MA) were explored. The results showed that plant dry weight (DW) [in shoot (29.8%, 8.74%) and in root (21.6%, 24.4%)] and chlorophyll [a (17.1%, 32.5%), b (10.1%, 30.9%)] declined in M and NM populations respectively, when exposed to Ni (400 μM). Conversely, the levels of MA [in shoot (37.0%, 32.0%) and in root (25.5%, 21.2%)], CA [in shoot (17.0%, 10.0%) and in root (47.9%, 37.2%)] and His [in shoot (by 1.59- and 1.34-fold) and in root (by 1.24- and 1.18-fold)] increased. Also, in the presence 400 μM Ni, the highest accumulation of Ni was observed in shoots of M (1392 μg/g DW) and NM (1382 μg/g DW). However, the application of SA and JA (especially in Ni 400 μM + SA 200 μM + JA 5 and 10 μM treatments) mitigated the harmful impact of Ni on physiological parameters. Also, a decreasing trend was observed in the contents of MA, CA, and His. The reduction of these compounds as important chelators of Ni caused a decrease in root-to-shoot Ni transfer and reducing accumulation in the shoots of both populations. The values of phytoremediation indices in both populations exposed to Ni (400 μM) were above one. In presence of the SA and JA, these indices showed a decreasing trend, although the values remained above one (BAC, BCF and TF > 1). Overall, the results indicated that SA and JA can reduce phytoremediation potential of the two populations through different mechanisms.

Ecological impacts and potential hazards of nickel on soil microbes, plants, and human health

Nickel (Ni) contamination poses a serious environmental concern, particularly in developing countries: where, anthropogenic activities significantly contributes to Ni accumulations in soils and waters. The contamination of agricultural soils with Ni, increases risks of its entry to terrestrial ecosystems and food production systems posing a threat to both food security and safety. We examined the existing published articles regarding the origin, source, accumulation, and transport of Ni in soil environments. Particularly, we reviewed the bioavailability and toxic effects of Ni to soil invertebrates and microbes, as well as its impact on soil-plant interactions including seed germination, nutrient uptake, photosynthesis, oxidative stress, antioxidant enzyme activity, and biomass production. Moreover, it underscores the potential health hazards associated with consuming crops cultivated in Ni-contaminated soils and elucidates the pathways through which Ni enters the food chain. The published literature suggests that chronic Ni exposure may have long-term implications for the food supply chain and the health of the public. Therefore, an aggressive effort is required for interdisciplinary collaboration for assessing and mitigating the ecological and health risks associated with Ni contamination. It also argues that these measures are necessary in light of the increasing level of Ni pollution in soil ecosystems and the potential impacts on public health and the environment.

Chromiomics: Chromium detoxification and approaches for engineering tolerance in plants

Chromium (Cr) is a heavy metal that poses a grave threat to the ecosystem including plants. Chromium is very harmful to plants due to its effects on many physiological and metabolic pathways culminating in a negative impact on plant's growth, development, and ability to take up nutrients. Plants have developed physiological, biochemical, and molecular ways of defense against Cr, such as by augmenting antioxidant potential to reduce reactive oxygen species (ROS). A number of genes have been discovered to play a significant role in the defense mechanisms of plants against Cr, for example, genes associated with the activation of phytochelatins, metallothioneins, and those of enzymes like glutathione-S-transferases. Along with this, a few miRNAs have been found to be associated in alleviating Cr stress and, to augment plant tolerance by controlling transcription factors, HSPs, and the expression of a few proteins and hormones. Defense pathway genes and miRNAs have been used for the generation of transgenic phytoremediator plants. Not only do the transgenic plants have a higher tolerance to Cr, but they also act as hyperaccumulators for Cr and have the potential to remediate other heavy metals. This article describes about environmental Cr contamination, Cr effects on plants, different genes and miRNAs involved in Cr stress mitigation and use of candidate genes, microRNAs for creating transgenic plant systems for phytoremediation, and the applications of CRISPR technology. It is expected that the integration of omics approach and advanced genomics will offer scope for more effective phytoremediation of Chromium in the coming years.

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.

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.

Phytoremediation of pollutants in oil-contaminated soils by Alhagi camelorum: evaluation and modeling

Phytoremediation is a cost-effective and environmentally friendly method, offering a suitable alternative to chemical and physical approaches for the removal of pollutants from soil. This research explored the phytoremediation potential of Alhagi camelorum, a plant species, for total petroleum hydrocarbons (TPHs) and heavy metals (HMs), specifically lead (Pb), chromium (Cr), nickel (Ni), and cadmium (Cd), in oil-contaminated soil. A field-scale study spanning six months was conducted, involving the cultivation of A. camelorum seeds in a nursery and subsequent transplantation of seedlings onto prepared soil plots. Control plots, devoid of any plants, were also incorporated for comparison. Soil samples were analyzed throughout the study period using inductively coupled plasma-optical emission spectroscopy (ICP‒OES) for HMs and gas chromatography‒mass spectrometry (GC‒MS) for TPHs. The results showed that after six months, the average removal percentage was 53.6 ± 2.8% for TPHs and varying percentages observed for the HMs (Pb: 50 ± 2.1%, Cr: 47.6 ± 2.5%, Ni: 48.1 ± 1.6%, and Cd: 45.4 ± 3.5%). The upward trajectory in the population of heterotrophic bacteria and the level of microbial respiration, in contrast to the control plots, suggests that the presence of the plant plays a significant role in promoting soil microbial growth (P < 0.05). Moreover, kinetic rate models were examined to assess the rate of pollutant removal. The coefficient of determination consistently aligned with the first-order kinetic rate model for all the mentioned pollutants (R2 > 0.8). These results collectively suggest that phytoremediation employing A. camelorum can effectively reduce pollutants in oil-contaminated soils.

Dynamic adaptation of the extremophilic red microalga Cyanidioschyzon merolae to high nickel stress

The order of Cyanidiales comprises seven acido-thermophilic red microalgal species thriving in hot springs of volcanic origin characterized by extremely low pH, moderately high temperatures and the presence of high concentrations of sulphites and heavy metals that are prohibitive for most other organisms. Little is known about the physiological processes underlying the long-term adaptation of these extremophiles to such hostile environments. Here, we investigated the long-term adaptive responses of a red microalga Cyanidioschyzon merolae, a representative of Cyanidiales, to extremely high nickel concentrations. By the comprehensive physiological, microscopic and elemental analyses we dissected the key physiological processes underlying the long-term adaptation of this model extremophile to high Ni exposure. These include: (i) prevention of significant Ni accumulation inside the cells; (ii) activation of the photoprotective response of non-photochemical quenching; (iii) significant changes of the chloroplast ultrastructure associated with the formation of prolamellar bodies and plastoglobuli together with loosening of the thylakoid membranes; (iv) activation of ROS amelioration machinery; and (v) maintaining the efficient respiratory chain functionality. The dynamically regulated processes identified in this study are discussed in the context of the mechanisms driving the remarkable adaptability of C. merolae to extremely high Ni levels exceeding by several orders of magnitude those found in the natural environment of the microalga. The processes identified in this study provide a solid basis for the future investigation of the specific molecular components and pathways involved in the adaptation of Cyanidiales to the extremely high Ni concentrations.

Concentrations and health risks of selected elements in leafy vegetables: a comparison between roadside open-air markets and large stores in Johannesburg, South Africa

This study compared concentrations and health risks of selected elements (Al, As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Zn) in leafy vegetables (coriander, lettuce, mint, spring onion, swiss chard) from roadside open-air markets (OM) and large stores (supermarkets: SM, vegetable markets: VM) in Johannesburg, South Africa. Along with washed leaves (OMW, SMW, VMW), unwashed OM leaves (OMUW) were assessed to investigate the contribution of deposition. The findings revealed that OMUW leaves had the highest concentrations of all elements. Furthermore, compared with washed leaves, OMUW leaves showed significantly higher (p < 0.05) mean concentrations of Cd, Hg, Ni and Pb, elements that typify the composition of polluted urban air. Bi- and multivariate analysis indicated anthropogenic origin of most elements in OM leaves and several in SMW and VMW leaves. Although only OMUW leaves exhibited hazard quotient above the safe threshold of 1 for Cd, Cr, As and Ni, hazard index exceeded this safe limit in all samples (OMUW (11.77) > OMW (1.83) > SMW (1.29) > VMW (1.01)). Determined cancer risk for Cd and As was greater than 1 × 10-6 in both washed and unwashed leaves, and the greatest cancer risk was estimated for OM leaves. Thorough washing of OM vegetables with water reduced non-carcinogenic risk (84%) and cancer risk (74‒87%) markedly. In conclusion, residents primarily relying on open-air markets for their regular leafy vegetable supplies might face far more severe lifelong health implications compared to customers of large stores in Johannesburg.

Nickel uptake in leafy greens from contaminated soil: an investigation into phytoavailability and health risk assessment using in vitro digestion model

Nickel (Ni) is a toxic metal that not only pollutes the environment but also causes harmful impacts on plant growth and human health. Therefore, it is crucial to assess the relationship between the phytoavailability of Ni in soil and its accumulation in edible and non-edible parts of vegetables. A pot experiment was conducted to investigate Ni uptake in three different leafy vegetables, spinach (Spinacia oleracea L.), lettuce (Lactuca sativa L.), and fenugreek (Trigonella foenum-graecum L.), grown in soil artificially contaminated with Ni at three different treatment levels (100 mg kg-1, 200 mg kg-1, and 300 mg kg-1). The potential dietary toxicity of these vegetables in humans was examined by using an in vitro digestion model. The lowest and highest chlorophyll contents were detected in lettuce at 300 mg kg-1 of Ni concentration and in control plants of spinach. Their values were 34.16 ± 3.01 (SPAD unit) and 53 ± 3.7673 (SPAD unit), respectively. Among the three vegetables, lettuce and spinach at 300 mg kg-1 exhibited the highest accumulation of Ni, with 43 mg kg-1 in edible parts and 182 mg kg-1 in non-edible parts. Furthermore, health risk index (HRI) values were found to be > 1 for lettuce and fenugreek at Ni concentrations of 200 and 300 mg kg-1 for both children and adults. The average bioaccessibility of Ni in lettuce, fenugreek, and spinach during the gastrointestinal phase was 32-23%, 24-10%, and 45-37%, respectively, at a Ni concentration of 300 mg kg-1. All three vegetables grown on Ni-contaminated soil may potentially contribute to food chain toxicity. The HRI values being > 1 suggest that these vegetables are unsafe for consumption. Monitoring of Ni concentration in leafy vegetables is essential to minimize human health risks associated with food chain contamination.

Nickel oxide nanoparticles induce cell wall modifications, root anatomical changes, and nitrosative signaling in ecotypes of Ni hyperaccumulator Odontarrhena lesbiaca

The industrial application and environmental release of nickel oxide NPs (NiO NPs) is increasing, but the details of their relationship with plants are largely unknown. In this work, the cellular, tissue, organ, and molecular level responses of three ecotypes of Ni hyperaccumulator Odontarrhena lesbiaca grown in the presence of high doses of NiO NP (250 mg/L and 500 mg/L) were studied. All three ecotypes showed a similar accumulation of Ni in the presence of nano Ni, and in the case of NiO NPs, the root-to-shoot Ni translocation was slighter compared to the bulk Ni. In all three ecotypes, the walls of the root cells effectively prevented internalization of NiO NPs, providing cellular defense against Ni overload. Exposure to NiO NP led to an increase in cortex thickness and the deposition of lignin-suberin and pectin in roots, serving as a tissue-level defense mechanism against excessive Ni. Exposure to NiO NP did not modify or cause a reduction in some biomass parameters of the Ampeliko and Loutra ecotypes, while it increased all parameters in Olympos. The free salt form of Ni exerted more negative effects on biomass production than the nanoform, and the observed effects of NiO NPs can be attributed to the release of Ni ions. Nitric oxide and peroxynitrite levels were modified by NiO NPs in an ecotype-dependent manner. The changes in the abundance and activity of S-nitrosoglutathione reductase protein triggered by NiO NPs suggest that the enzyme is regulated by NiO NPs at the post-translational level. The NiO NPs slightly intensified protein tyrosine nitration, and the slight differences between the ecotypes were correlated with their biomass production in the presence of NiO NPs. Overall, the Odontarrhena lesbiaca ecotypes exhibited tolerance to NiO NPs at the cellular, tissue, organ/organism and molecular levels, demonstrating various defense mechanisms and changes in the metabolism of reactive nitrogen species metabolism and nitrosative protein modification.

Intestinal microbiota promoted NiONPs-induced liver fibrosis via effecting serum metabolism

Nickel oxide nanoparticles (NiONPs) are toxic heavy metal compounds that induce liver fibrosis and metabolic disorders. Current research shows that the intestinal microbiota regulates liver metabolism through the gut-liver axis. However, it is unclear whether NiONPs affect the intestinal microbiota and the relationship between microbiota and liver metabolic disorders. Therefore, in this study, we established liver fibrosis model by administering 0.015, 0.06 and 0.24 mg/mL NiONPs through tracheal instillation twice a week for 9 weeks in rats, then we collected serum and fecal sample for whole metabolomics and metagenomic sequencing. As the result of sequencing, we screened out seven metabolites (beta-D-glucuronide, methylmalonic acid, linoleic acid, phosphotidylcholine, lysophosphatidylinositol, docosapentaenoic acid and progesterone) that related to functional alterations (p < 0.05), and obtained a decrease of probiotics abundances (p < 0.05) as well as a variation of the microbiota enzyme activity (p < 0.05), indicating that NiONPs inhibited the proliferation of probiotics. As the result of correlation analysis, we found a positive correlation between differential metabolites and probiotics, such as lysophosphatidylinositol was positively correlated with Desulfuribacillus, Jeotgallibacillus and Rummeliibacillus (p < 0.05). We also found that differential metabolites had correlations with differential proteins and enzymes of intestinal microbiota, such as glucarate dehydratase, dihydroorotate dehydrogenase and acetyl-CoA carboxylase (p < 0.05). Finally, we screened six metabolic pathways with both differential intestinal microbiota enzymes and metabolites were involved, such as pentose and glucuronate interconversions, and linoleic acid metabolism. In vitro experiments showed that NiONPs increased the transcriptional expression of Col1A1 in LX-2 cells, while reducing the mRNA expression of serine/threonine activators, acetyl coenzyme carboxylase, and lysophosphatidylinositol synthase, and short chain fatty acid sodium butyrate can alleviate these variation trends. The results proved that the intestinal microbiota enzyme systems were associated with serum metabolites, suggesting that the disturbance of intestinal microbiota and reduction of probiotics promoted the occurrence and development of NiONPs-induced liver fibrosis by affecting metabolic pathways.

Glycine-Rich RNA-Binding Protein AtGRP7 Functions in Nickel and Lead Tolerance in Arabidopsis

Plant glycine-rich RNA-binding proteins (GRPs) play crucial roles in the response to environmental stresses. However, the functions of AtGRP7 in plants under heavy metal stress remain unclear. In the present study, in Arabidopsis, the transcript level of AtGRP7 was markedly increased by Ni but was decreased by Pb. AtGRP7-overexpressing plants improved Ni tolerance, whereas the knockout mutant (grp7) was more susceptible than the wild type to Ni. In addition, grp7 showed greatly enhanced Pb tolerance, whereas overexpression lines showed high Pb sensitivity. Ni accumulation was reduced in overexpression lines but increased in grp7, whereas Pb accumulation in grp7 was lower than that in overexpression lines. Ni induced glutathione synthase genes GS1 and GS2 in overexpression lines, whereas Pb increased metallothionein genes MT4a and MT4b and phytochelatin synthase genes PCS1 and PCS2 in grp7. Furthermore, Ni increased CuSOD1 and GR1 in grp7, whereas Pb significantly induced FeSOD1 and FeSOD2 in overexpression lines. The mRNA stability of GS2 and PCS1 was directly regulated by AtGRP7 under Ni and Pb, respectively. Collectively, these results indicate that AtGRP7 plays a crucial role in Ni and Pb tolerance by reducing Ni and Pb accumulation and the direct or indirect post-transcriptional regulation of genes related to heavy metal chelators and antioxidant enzymes.

Melatonin as a key regulator in seed germination under abiotic stress

Seed germination (SG) is the first stage in a plant's life and has an immense importance in sustaining crop production. Abiotic stresses reduce SG by increasing the deterioration of seed quality, and reducing germination potential, and seed vigor. Thus, to achieve a sustainable level of crop yield, it is important to improve SG under abiotic stress conditions. Melatonin (MEL) is an important biomolecule that interplays in developmental processes and regulates many adaptive responses in plants, especially under abiotic stresses. Thus, this review specifically summarizes and discusses the mechanistic basis of MEL-mediated SG under abiotic stresses. MEL regulates SG by regulating some stress-specific responses and some common responses. For instance, MEL induced stress specific responses include the regulation of ionic homeostasis, and hydrolysis of storage proteins under salinity stress, regulation of C-repeat binding factors signaling under cold stress, starch metabolism under high temperature and heavy metal stress, and activation of aquaporins and accumulation of osmolytes under drought stress. On other hand, MEL mediated regulation of gibberellins biosynthesis and abscisic acid catabolism, redox homeostasis, and Ca2+ signaling are amongst the common responses. Nonetheless factors such as endogenous MEL contents, plant species, and growth conditions also influence above-mentioned responses. In conclusion, MEL regulates SG under abiotic stress conditions by interacting with different physiological mechanisms.

ZnO nanoparticles mediated by Azadirachta indica as nano fertilizer: Improvement in physiological and biochemical indices of Zea mays grown in Cr-contaminated soil

The current investigation aimed at evaluating the impact of Azadirachta indica-mediated zinc oxide nanoparticles (Ai-ZnONPs) on the growth and biochemical characteristics of maize (sweet glutinous 3000) under exposure to 50 mg kg-1Ai-ZnONPs with Cr (VI) concentrations of 50 and 100 mg kg-1. The results indicate that plants exposed to Cr (VI) only experienced a decline in growth parameters. Conversely, the inclusion of Ai-ZnONPs caused a noteworthy increase in physiological traits. Specifically, shoot and root fresh weight increased by 28.02% and 16.51%, and 63.11% and 97.91%, respectively, when compared to Cr-50 and 100 treatments. Additionally, the SPAD chlorophyll of the shoot increased by 91.08% and 15.38% compared to Cr-50 and 100 treatments, respectively. Moreover, the antioxidant enzyme traits of plant shoot and root, such as superoxide dismutase (SOD 7.44% and 2.70%, and 4.45% and 3.53%), catalase (CAT 1.18% and 3.20%, and 5.03% and 5.78%), and peroxidase (POD 0.31% and 5.55%, and 4.72% and 3.61%), exhibited significant increases in Cr 50 and 100 treatments, respectively. The addition of Ai-ZnONPs to the soil also enhanced soil nutrient status and reduced Cr (VI) concentrations by 40.69% and 19.82% compared to Cr-50 and 100 treated soils. These findings suggest that Ai-ZnONPs can trigger the activation of biochemical pathways that enable biomass accumulation in meristematic cells. Further investigations are required to elucidate the mechanisms involved in growth promotion.

Countenance and implication of Β-sitosterol, Β-amyrin and epiafzelechin in nickel exposed Rat: in-silico and in-vivo approach

The detrimental impact of reactive oxygen species on D.N.A. repair processes is one of the contributing factors to colon cancer. The idea that oxidative stress may be a significant etiological element for carcinogenesis is currently receiving more and more support. The goal of the current study is to evaluate the anti-inflammatory and anticancer activity of three powerful phytocompounds-sitosterol, amyrin, and epiafzelechin-alone and in various therapeutic combinations against colon cancer to identify the critical mechanisms that mitigate nickel's carcinogenic effect. To evaluate the ligand-protein interaction of four selected components against Vascular endothelial growth factor (VEGF), Matrix metalloproteinase-9 (MMP9) inhibitor and Interleukin-10 (IL-10) molecular docking approach was applied using PyRx bioinformatics tool. For in vivo analysis, hundred albino rats were included, divided into ten groups, each containing ten rats of weight 160-200 g. All the groups were injected with 1 ml/kg nickel intraperitoneally per week for three months, excluding the negative control group. Three of the ten groups were treated with β-sitosterol (100 mg/kg b wt), β-amyrin (100 mg/kg b wt), and epiafzelechin (200 mg/kg b wt), respectively, for one month. The later four groups were fed with combinatorial treatments of the three phyto compounds for one month. The last group was administered with commercial drug Nalgin (500 mg/kg b wt). The biochemical parameters Creatinine, Protein carbonyl, 8-hydroxydeoxyguanosine (8-OHdG), VEGF, MMP-9 Inhibitor, and IL-10 were estimated using ELISA kits and Glutathione (G.S.H.), Superoxide dismutase (S.O.D.), Catalase (C.A.T.) and Nitric Oxide (NO) were analyzed manually. The correlation was analyzed through Pearson's correlation matrix. All the parameters were significantly raised in the positive control group, indicating significant inflammation. At the same time, the levels of the foresaid biomarkers were decreased in the serum in all the other groups treated with the three phytocompounds in different dose patterns. However, the best recovery was observed in the group where the three active compounds were administered concomitantly. The correlation matrix indicated a significant positive correlation of IL-10 vs VEGF (r = 0.749**, p = 0.009), MMP-9 inhibitor vs SOD (r = 0.748**, p = 0.0 21). The study concluded that the three phytocompounds β-sitosterol, β-amyrin, and epiafzelechin are important anticancer agents which can target the cancerous biomarkers and might be used as a better therapeutic approach against colon cancer soon.

Nickel in foodstuffs available on the Luxembourgish market and dietary intake

Nickel is a food contaminant of natural or anthropogenic origin. Monitoring of contaminants in food in general allows obtaining an overview on the presence of substances that are undesirable to health. The aim of this study was to analyse nickel content in food of non-animal origin and beverages sold in Luxembourg to determine the exposure of the population to this contaminant. In total, 660 samples were analysed in the timeframe from 2017 to 2021. The results demonstrate high concentrations of nickel in cashew nuts, walnuts, hemp and sunflower seeds, dried peas, oregano, and cocoa powder. Surveillance of contaminants in food allows identifying contributors to the chronic and acute exposure of nickel in order to potentially set official maximum levels in European legislation in the future, allowing for better enforcement actions in case of contaminated products and increasing consumer protection.

Auxin homeostasis in plant responses to heavy metal stress

Expeditious industrialization and anthropogenic activities have resulted in large amounts of heavy metals (HMs) being released into the environment. These HMs affect crop yields and directly threaten global food security. Therefore, significant efforts have been made to control the toxic effects of HMs on crops. When HMs are taken up by plants, various mechanisms are stimulated to alleviate HM stress, including the biosynthesis and transport of auxin in the plant. Interestingly, researchers have noted the significant potential of auxin in mediating resistance to HM stress, primarily by reducing uptake of metals, promoting chelation and sequestration in plant tissues, and mitigating oxidative damage. Both exogenous administration of auxin and manipulation of intrinsic auxin status are effective strategies to protect plants from the negative consequences of HMs stress. Regulation of genes and transcription factors related to auxin homeostasis has been shown to be related to varying degrees to the type and concentration of HMs. Therefore, to derive the maximum benefit from auxin-mediated mechanisms to attenuate HM toxicities, it is essential to gain a comprehensive understanding of signaling pathways involved in regulatory actions. This review primarily emphases on the auxin-mediated mechanisms participating in the injurious effects of HMs in plants. Thus, it will pave the way to understanding the mechanism of auxin homeostasis in regulating HM tolerance in plants and become a tool for developing sustainable strategies for agricultural growth in the future.