Jarin et al. 2025 — Plant responses to heavy metal stresses, defense strategies, and nanoparticle-assisted remediation

Jarin, Khan, Apon, Islam, Rahat, Akter, Anik, H. M. Nguyen, T. T. Nguyen, Ha, and Tran (Department of Agronomy and Department of Genetics and Plant Breeding, Gazipur Agricultural University, Bangladesh; Institute of Genomics for Crop Abiotic Stress Tolerance, Texas Tech University, USA; Bangladesh Sugarcrop Research Institute; Department of Agroforestry, Bangladesh Agricultural University; Vietnam National University of Agriculture; corresponding authors Khan, Ha, and Tran) review the published evidence on plant morphological, physiological, biochemical, and molecular responses to heavy metal (HM) stress, the defense strategies plants deploy against HM toxicity, and the emerging use of engineered and biogenic nanoparticles (NPs) for HM remediation in soils and water. The paper is a “Review” article in Plants (MDPI) covering 244+ cited references, four figures (Figure 1 essential vs non-essential metal toxicity targets in plants; Figure 2 HM-stress disruption of photosynthesis, ABA/ROS/NO signalling, and stomatal regulation; Figure 3 microbial enhancement of detoxification, nutrient transport, and biomass accumulation; Figure 4 cellular-compartment cascade of HM detoxification through cell wall, plasma membrane, cytosol, tonoplast, and vacuole), and seven synthesis tables (Table 1 essentiality and adequate/toxic levels for 12 metals in plants; Table 2 morphological/physiological/biochemical responses to HM stress across nine crop species and one weed; Table 3 antioxidant enzyme responses across twelve plant species; Table 4 five signalling pathways with key components, target metals, responses, and gene families; Table 5 transcription-factor families activated under HM stress in seven plant species; Table 6 seven nanoparticle types with target metals, percent HM reduction, and key findings; Table 7 fifteen microbial/plant-extract-based NP biosyntheses with their phytotoxicity-alleviation effects). The review reports no primary chemical, occurrence, or exposure measurements in any food, beverage, supplement, personal-care, or environmental matrix; its value to the wiki is conceptual background on plant-side HM biology and a structured catalogue of nanoparticle-assisted remediation evidence relevant to the remediation-evidence chapter.

Why this matters

• It catalogues, in Table 1, the essentiality status and adequate/toxic concentration ranges (mg kg⁻¹ DW) for twelve metals in plants: five non-essential toxic metals (As, Cd, Cr, Hg, Pb) with toxic thresholds ≥1 to ≥30 mg kg⁻¹ DW depending on the metal; six essential micronutrients (Cu, Fe, Mn, Mo, Zn, Ni) with adequate ranges (e.g., Cu 5–30, Fe 50–250, Zn 25–150, Ni 0.1–10 mg kg⁻¹ DW) and toxic-onset thresholds (Cu >30, Fe >500, Mn >1000, Mo >10, Zn >150, Ni >50 mg kg⁻¹ DW); and Co as beneficial for nitrogen fixation in legumes (0.02–2 mg kg⁻¹ DW adequate, >10 mg kg⁻¹ DW toxic). The HMI-priority subset (Pb, tAs, Cd, tHg, Ni, Cr) is covered with toxic-threshold attributions traced to specific reference numbers in the original table.
• It quantifies HM impacts on germination and seedling establishment: HM toxicity reduces germination rates by 20–50% and inhibits shoot and root development by 30–60% across various crops; Cr specifically inhibits seed germination by 20–50% via amylase suppression, sugar-transport alteration, and photosynthetic-efficiency reduction; Pb impairs root and shoot growth by 30–60% across various crops with chlorophyll synthesis, stomatal regulation, and photosystem II efficiency disruption. These integer-percent ranges trace to refs [39–42] and are the kind of quantitative anchor the wiki’s remediation-evidence and lead / chromium pages can cite for the phytotoxicity threshold framing.
• It quantifies arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (ECM) contributions to HM tolerance: AMF can retain 40–70% of metals in root tissues via chelation, adsorption, and organic acid release; glomalin (an AMF-secreted glycoprotein with high metal-binding affinity) stabilises soil aggregates and reduces HM bioavailability; AMF inoculation has been shown to enhance P uptake and restrict HM transport to shoots in soybean (Glycine max), and eggplants (Solanum melongena) inoculated with AMF accumulated less Pb in fruits. These integer-percent and crop-specific anchors trace to refs [128–139].
• It quantifies engineered/biogenic nanoparticle HM-reduction efficacy in Table 6 with HM-specific percent ranges: ZnO NPs in rice/fenugreek/Leucaena leucocephala reduced Pb by 79–85%, Cd by 80–87%, Cr by 38–81%, Cu by 60%; CeO₂ NPs in rice reduced Cd accumulation by 8.4%; astaxanthin-functionalised Au NPs in rice reduced Cd by 26–86%; TiO₂ NPs in rice and cucumber reduced Pb, As, and Al by 34–97%; Fe₃O₄ NPs in wheat reduced Cd in roots by 24–68% and in shoots by 11–100%; Se NPs in coriander and pak choi reduced Cd by 21–31%, Pb by 5–30%, and Hg by 3–23%. Refs [213–221]. This table is the wiki’s cleanest single-source citation for the “nanoparticle-assisted phytoremediation” claim space.
• It quantifies plant-growth enhancement under HM stress with NP application: engineered and biogenic NPs (e.g., ZnO, Fe₃O₄) improve metal immobilisation, reduce bioavailability, and enhance plant growth by 15–35% under HM stresses. This integer range traces to refs [205–221] and is useful as a hedge against the naïve “more NP = more remediation” framing — the review explicitly notes that excessive NP doses may induce phytotoxicity.
• It cross-references 15 microbial isolates and plant extracts (Table 7) used for biogenic NP synthesis, including Pseudomonas aeruginosa (CdS NPs, EPS-enriched), Bacillus subtilis (gold NPs, antifungal biocontrol), E. coli (silver NPs, rapid Ag⁺ reduction), Chlorococcum algae (Fe NPs removing 92% Cr vs 25% by bulk Fe), and biogenic Fe-Mn oxides from Pseudomonas sp. (As(III) → As(V) conversion for arsenic remediation). The microbial biosynthesis catalogue is potentially relevant to WikiBiome federation around the heavy-metal-microbiome exposure axis, though the review’s microbiome treatment is rhizosphere-focused rather than gut-focused.
• It documents the upstream-downstream signalling cascade in Figure 2 with explicit pathway integration: HM stress → glucose-metabolism and TCA-cycle disruption → photosynthetic dysfunction; HM stress → ABA induction → ABI1/PYR/PYL receptor binding → PP2C inhibition → OST1 activation → stomatal closure; HM stress → ROS overproduction → NO → RNS → 8-nitro-cGMP → stomatal closure and vacuolar turgor loss. This integrated framing is the load-bearing concept for the wiki’s discussion of HM phytotoxicity at the whole-plant productivity level.
• It anchors the multi-omics and CRISPR/Cas9 future-research framing in Section 8: CRISPR/Cas9 genome editing of WRKY/MYB/bZIP transcription factors and HMA3/Nramp metal transporters has been shown in rice, Arabidopsis, and wheat to improve growth, stress tolerance, and yield under HM exposure; the review proposes five Future Research Directions including multi-omics regulatory-network analysis, scalable field-applicable phytoremediation protocols, and ecological-risk evaluation of NP fate.

Key concepts and structure

The article has eight top-level sections plus references (244+ entries). Section 1 (Introduction) frames HM contamination as a threat to environmental sustainability, food safety, and agricultural productivity, defines HMs as dense metallic elements with densities exceeding 5 g cm⁻³, and identifies As, Cd, Cr, Hg, and Pb as the five HMs of primary concern in soils, water, and wastewater. Section 2 (“Roles of Heavy Metals in Plants”) catalogues essentiality and adequate/toxic concentration thresholds for twelve metals (Table 1) and quantifies HM phytotoxicity at germination, root-elongation, and shoot-development stages with percent-range anchors. Section 3 (“Morphological, Physiological, and Biochemical Responses to Heavy Metal Stresses”) covers stomatal dysfunction, photosynthetic impairment, water-use-efficiency reduction, and lipid peroxidation across nine crop and weed species (Table 2); includes the integrated cellular-compartment cascade through cell wall, plasma membrane, cytosol, tonoplast, and vacuole (Figure 4). Section 4 (“Disruption of Cell Membrane Integrity, Oxidative Homeostasis, and Enzymatic Activities”) covers HM-induced ROS generation via Haber–Weiss and Fenton reactions, methylglyoxal accumulation, glutathione depletion, direct ROS generation by redox-active metals (Cu, Fe, Cr), indirect ROS accumulation via antioxidant-defense impairment by redox-inactive metals (Cd, Pb, Zn), and cofactor displacement (Cd in Zn-finger TFs, Cd in calmodulin, Pb interference with chlorophyll structure). Section 5 (“Plants’ Resistance Mechanisms to Heavy Metal Stresses”) covers the avoidance/tolerance dichotomy and unfolds into four subsections: 5.1 mycorrhizal immobilisation (AMF, ECM, glomalin, 40–70% root-tissue metal retention); 5.2 root-mediated mechanisms and phytochelatin-driven detoxification (root exudates, organic acids, histidine/nicotianamine chelation, PC/MT chelation, vacuolar sequestration via ABC transporters and metal/H⁺ antiporters); 5.3 antioxidant responses (SOD, CAT, POD, APX, GR responses across twelve plant species in Table 3); 5.4 signalling-pathway and gene-expression regulation (calcium-dependent, MAPK cascade, ROS, hormonal, and crosstalk pathways with their key components, target metals, responses, and gene families in Table 4; transcription factors WRKY, MYB, bZIP, NAC, HSF activated under HM stress across seven plant species in Table 5; transgenic and CRISPR/Cas9 approaches for tolerance enhancement). Section 6 (“Nanoparticle-Mediated Alleviation of Heavy Metal Stresses in Plants”) catalogues seven nanoparticle types (ZnO, CeO₂, astaxanthin-Au, TiO₂, Fe₃O₄, Se, graphene oxide) with target plants, target metals, percent HM reduction, and key findings (Table 6); discusses dose-dependence, optimal vs phytotoxic NP levels, environmental NP fate, and ecological risk. Section 7 (“Nanoparticle-Assisted Bioremediation Against Heavy Metal Stresses”) covers microbial biosynthesis of NPs (Pseudomonas aeruginosa, Bacillus subtilis, Rhizobium, Staphylococcus aureus, Aspergillus, Rhizopus, Penicillium), plant-extract-mediated NP synthesis (Camellia sinensis, Citrus limon, Mangifera indica), and the comparative efficacy of biogenic MnO from Pseudomonas putida MnB1 (7–8 times greater HM adsorption than abiotic forms); fourteen microbial isolates and plant extracts catalogued in Table 7. Section 8 (Conclusions and Future Research Directions) names five strategic priorities: (i) deciphering plant-microbiome-NP interactions to optimise rhizosphere processes for HM detoxification; (ii) applying synthetic biology and CRISPR/Cas9 gene editing to key regulatory genes, TFs, and transporters; (iii) integrating multi-omics tools to unravel regulatory networks and crosstalk between physiological, biochemical, and molecular pathways; (iv) evaluating long-term ecological risks and field performance of NPs with emphasis on safe design, environmental fate, and regulatory frameworks; (v) developing scalable, field-applicable nanoparticle-assisted phytoremediation protocols combining engineered plants, beneficial microbes, and smart nanomaterials for site-specific remediation.

Table 1 — Roles and adequate/toxic levels of heavy metals in plants (source p. 3–4, full transcription)

The Table 1 grading is in mg kg⁻¹ DW (dry weight) throughout. The non-essential toxic metals (Cd, Pb, As, Cr, Hg) lack defined “adequate” levels because they have no plant nutritional function; their entries report toxic thresholds only. The essential micronutrients (Cu, Fe, Mn, Mo, Zn, Ni) have both adequate and toxic ranges, with Co treated as beneficial for legume nitrogen fixation.

Table 2 — Morphological, physiological, and biochemical responses of plants to HM stresses (source p. 5–6, full transcription)

Twelve rows across nine crop species (rice, wheat, maize, sunflower, lentil, pigeon pea, Siris tree, Indian mustard, Silene compacta/Thalpsi ochroleucum, Arabidopsis, duckweed) and ten metal-treatment combinations. The pattern of responses across species — increased lipid peroxidation, oxidative stress, reduced shoot/root development, decreased chlorophyll content, increased H₂O₂ and TBARS levels — is broadly consistent and serves as the substrate for the integrated Section 4 cellular-disruption framing.

Table 3 — Antioxidant enzyme responses in plants exposed to HM stresses (source p. 11, full transcription)

Twelve plant species and twelve metal-treatment combinations. The vocabulary (SOD, CAT, APX, GPX, POD, GR) is the standard antioxidant-enzyme repertoire; the response direction (increases or decreases) is metal- and species-specific.

Table 4 — Key signalling pathways and molecular components involved in HM stress responses (source p. 12, full transcription)

Five canonical signalling pathways with their key components, target metals, responses, and identified gene families. The MAPK cascade (MAPKKK → MAPKK → MAPK) and ROS signalling rows are the load-bearing entries for the integration with TF activation discussed in Section 5.4 and Table 5.

Table 5 — Roles of transcription factors in plant adaptation to HM stresses (source p. 13, full transcription)

Sixteen TF-gene-plant rows across seven plant species. Arabidopsis carries the highest density (five entries spanning MYB, WRKY, bZIP, and the MYB49/AB15 Cd-uptake regulatory pair); rice carries four entries spanning MYB, bZIP, and WRKY. The HSF/WRKY/MYB/bZIP/NAC TF families are the load-bearing TF vocabulary for HM-stress transcriptional regulation across the wiki’s discussion of Cd and Pb tolerance mechanisms.

Table 6 — Nanoparticles for heavy metal stress mitigation in plants (source p. 14–15, full transcription)

Seven nanoparticle types with target plants, target metals, percent reduction (where reported), key findings, and reference numbers. The percent-reduction column anchors the integer-range NP-efficacy claims used in the Why this matters section; the CeO₂ row reports a single 8.4% figure rather than a range, and the graphene oxide row reports no percent reduction because the cited study focused on antioxidant-enzyme and biomass outcomes rather than tissue HM concentration.

Table 7 — Microbial and plant-based biosynthesis of nanoparticles and their role in mitigating HM phytotoxicity (source p. 15–16, full transcription)

Fifteen microbial isolate/plant extract entries across eight NP types (silver, gold, ZnO, lead, iron, TiO₂, biogenic Fe-Mn oxides, CdS). The microbial vocabulary spans bacterial (E. coli, Pseudomonas stutzeri, Bacillus subtilis, Aspergillus japonicus, Aspergillus niger, Aspergillus oryzae, Pseudomonas sp., P. aeruginosa, Clostridium pasteurianum) and algal (Chlorococcum, green algae) genera plus plant-extract sources (Solanum xanthocarpum berry extract, Convolvulus arvensis leaf extract, Citrus limon leaf extract). The iron-NP row from Chlorococcum algae (92% Cr removal vs 25% by bulk Fe) is the most striking biogenic-vs-abiotic efficacy comparison in the table.

Phytochelatin, metallothionein, and integrated detoxification (source Section 5.2, p. 9–10)

Plants counteract HM toxicity through the synthesis of phytochelatins (PCs) and metallothioneins (MTs), which chelate metals and reduce cytosolic toxicity. PCs preferentially bind Cd²⁺ and As³⁺, forming stable vacuolar complexes that limit cytosolic accumulation and oxidative damage; MTs exhibit variable metal-binding affinities depending on plant species. Cd²⁺ is rapidly chelated in roots, reducing shoot translocation, whereas As³⁺ complexes may be redistributed gradually. In Arabidopsis thaliana, Cd–PC complexes accumulate mainly in roots; in rice (Oryza sativa), greater root-to-shoot Cd translocation occurs. PC synthesis is rapidly upregulated following HM exposure, utilising cytosolic glutathione present in millimolar concentrations as substrate; once formed, PC-metal complexes are actively transported into the vacuole via tonoplast-localised ATP-Binding Cassette transporters or metal/H⁺ antiporters. The cellular cascade is summarised in Figure 4 as five compartments (cell wall → plasma membrane → cytosol → tonoplast → vacuole) with primary detoxification occurring at the plasma membrane and cytosol, and final sequestration at the vacuole. In addition to PC- and MT-mediated chelation, plants utilise five cellular barriers and strategies: (i) cell wall adsorption of HMs through pectin and lignin ion exchange; (ii) downregulation of specific membrane transporters to reduce metal influx; (iii) intracellular chelation via PCs, MTs, organic acids (citric, malic, oxalic), and amino acids (histidine, nicotianamine); (iv) tonoplast-mediated minimisation of HM movement back into the cytoplasm; (v) conversion of PC-metal complexes into insoluble metal deposits within vacuoles.

Signalling pathway integration and ABA/ROS/NO cascade (source Section 3 + Figure 2, p. 7)

HM stress increases ABA synthesis, which activates the OST1 (Open Stomata 1) protein kinase while inhibiting protein phosphatase 2C (PP2C) activity. Blocking PP2Cs prevents protein dephosphorylation, relieving the suppression of ABA signalling. OST1 is one of the main targets of PP2Cs and transmits the ABA signal by phosphorylating downstream targets and enhancing ROS production via NADPH oxidase activation. Nitric oxide (NO) and reactive nitrogen species (RNS) act as secondary messengers, amplifying the signalling cascade under HM stress; as a redox-active free radical, NO can neutralise HM-induced ROS directly or by activating antioxidant defenses. However, an imbalance between NO, ROS, and antioxidant activity can trigger oxidative stress. HM stress disrupts the photosynthetic electron transport chain, leading to decreased photosystem II activity; at elevated concentrations, HM stress disturbs the light-harvesting complex, particularly the transition between its functional states, resulting in antenna complex disorganisation and compromised photochemical efficiency. The integrated cascade (Figure 2) collectively reduces photosynthesis, transpiration, respiration, nutrient uptake, leaf area, CO₂ uptake, water uptake, ion balance, stomatal conductance, stomatal number, stomatal size, and cell membrane integrity, while increasing ion imbalance and cell membrane damage.

Mycorrhizal immobilisation and glomalin (source Section 5.1, p. 8–9)

Mycorrhizal fungi, particularly arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (ECM), play a vital role in enhancing plant tolerance to HM stress by forming symbiotic associations with roots. These fungi reduce HM uptake through chelation, adsorption, and release of organic acids and glomalin. Extraradical hyphae of AMF extend beyond the root zone, improving nutrients (N, P, K) uptake, which in turn enhances plant growth and HM stress resistance. AMF can retain 40–70% of metals in root tissues via chelation, while extraradical and intraradical hyphae provide additional binding surfaces containing glucan, chitin, and galactosamine polymers. Glomalin (an AMF-secreted glycoprotein with high metal-binding affinity) stabilises soil aggregates and reduces HM bioavailability. Evidence shows that AMF inoculation promotes HM retention in roots and reduces movement to aerial tissues, often resulting in significantly lower concentrations in edible parts: AMF inoculation enhanced P uptake and restricted HM transport to shoots in soybean (Glycine max); eggplants (Solanum melongena) inoculated with AMF accumulated less Pb in fruits. ECM form a fungal sheath around roots and secrete extracellular polymers and organic acids that immobilise metals in the rhizosphere; they are particularly important for woody plants and act primarily as barriers to HM entry, whereas AMF combine nutrient acquisition with HM detoxification.

Methods (brief)

This is a structured narrative review article. The authors do not describe a formal PRISMA-style search strategy or risk-of-bias methodology. The article was received 29 September 2025, revised 29 November 2025, accepted 9 December 2025, and published 16 December 2025 in Plants 2025, Vol 14, Article 3834 (DOI 10.3390/plants14243834). Academic Editors: Krzysztof Sitko and Miguel Pedro Mourato. Funding: no external funding. The Acknowledgments section credits the University Grants Commission of Bangladesh for supporting the project “Morpho-physiological and biochemical changes of cowpea genotypes under saline conditions”, the Bangladesh Ministry of Science and Technology special research grant 2022–2023 (SRG-221152), and the Research Management Wing of Gazipur Agricultural University (Project ID 05/2020). The authors disclose that OpenAI ChatGPT (GPT-5-mini) was used for language refinement and grammar correction during manuscript preparation, with the authors taking full responsibility for the content; this is a notable disclosure since GPT-edited prose is a developing practice in MDPI’s editorial workflow and the disclosure is best practice. Data Availability Statement: “No new data were created or analyzed in this study. Data sharing is not applicable to this article.” Author Contributions: Conceptualization A.S.J. and M.A.R.K.; visualisation A.S.J. and M.A.R.K.; writing — original draft A.S.J. and M.A.R.K.; supervision M.A.R.K.; writing — review and editing M.A.R.K., T.A.A., M.A.I., A.R., M.A., T.R.A., H.M.N., T.T.N., C.V.H., L.-S.P.T. Conflicts of Interest: none declared. The journal (MDPI) is open access; the article is published under CC BY 4.0. The 244+ reference set spans plant physiology (Plants, Plant Cell Reports, Plant Physiology and Biochemistry, Frontiers in Plant Science), environmental science (Environmental Pollution, Science of the Total Environment, Ecotoxicology and Environmental Safety, Chemosphere), and nanotechnology (Hybrid Advances, Environmental Chemistry Letters, Ecotoxicology and Environmental Safety). The corresponding authors (Khan at Gazipur, Ha and Tran at Texas Tech) span Bangladesh and Texas Tech’s Institute of Genomics for Crop Abiotic Stress Tolerance; the Lam-Son Phan Tran lab at Texas Tech has substantial prior work on plant stress tolerance and is a recognisable group in the abiotic-stress signalling literature.

Implications

• Certification: The review contributes no occurrence data, no exposure data, and no analytical-method or LOD specifications, so it does not move any HMTc threshold-setting work directly. Its quantitative anchors — germination-rate reductions of 20–50%, root/shoot inhibition of 30–60%, AMF metal retention of 40–70%, NP-mediated HM-reduction ranges of 8.4% to 97%, plant-growth enhancement under NP application of 15–35% — are agronomic-scale phytotoxicity and phytoremediation metrics rather than food-safety occurrence values. The Table 1 toxic-threshold values (Cd ≥5, Pb ≥30, Cr ≥5, As ≥5, Hg ≥1 mg kg⁻¹ DW) are plant-tissue thresholds for growth inhibition, not human-exposure regulatory ceilings, and should not be conflated with food-as-consumed limits. Indirect relevance: the review’s framing of nanoparticle-assisted phytoremediation as a soil-decontamination intervention may inform HMTc supply-chain audit guidance for crops grown on legacy contaminated soils, but this is a downstream implication not advanced by the source itself.
• App: No routing to ingredient or product pages. The review provides background reading for cadmium, lead, arsenic, nickel, chromium, mercury, and remediation-evidence on plant-side biology of metal uptake, chelation, antioxidant defense, and remediation; it does not bear on contamination occurrence in any specific food or personal-care matrix.
• Courses: Useful as a single-source orientation to the integrated cellular cascade (Figure 4: cell wall → plasma membrane → cytosol → tonoplast → vacuole), the antioxidant-enzyme repertoire (SOD, CAT, APX, POD, GR, GPX in Table 3), the five canonical signalling pathways (Table 4: calcium-dependent, MAPK, ROS, hormonal, crosstalk), the TF families (WRKY, MYB, bZIP, NAC, HSF in Table 5), and the seven engineered/biogenic nanoparticle classes (Table 6: ZnO, CeO₂, Au-Ast, TiO₂, Fe₃O₄, Se, graphene oxide). Should not be cited as the authority for any specific quantitative crop-level HM-reduction claim; trace claims to the cited primary studies first (e.g., the ZnO-NP-mediated Pb reduction of 79–85% attributed to refs [213,214]).
• Microbiome: Moderately relevant. The review discusses rhizosphere microbiology (AMF, ECM, glomalin) as a modulator of HM tolerance and catalogues microbial NP biosynthesis (Table 7) for bioremediation; however, the microbiome framing is rhizosphere-focused rather than gut-focused, and the review does not engage the heavy-metal–gut-microbiome exposure axis directly. The microbial-isolate catalogue may be tangentially useful for WikiBiome federation work on biogenic-NP synthesis but not for primary microbiome–exposure mapping.

Limitations

This is a structured narrative review without a declared search strategy, PRISMA flow, risk-of-bias assessment, or quantitative synthesis. The 244+ reference set is broad but the review’s coverage of plant-physiology, environmental-chemistry, and nanotechnology literatures is not exhaustive; reference selection appears weighted toward MDPI and Frontiers journals plus the abiotic-stress signalling literature familiar to the Tran group at Texas Tech. The metals coverage spans both HMI-priority analytes (Cd, Pb, As, Ni, Cr, Hg) and non-HMI metals (Cu, Fe, Mn, Mo, Zn, Co); As is treated under the general “As” label without iAs vs tAs distinction (the iAs/AsV uptake-pathway framing in Section 2 distinguishes arsenite from arsenate at the chemical level but the toxicity-threshold and antioxidant-response framings throughout the review use unspeciated “As”); Hg is treated as a single category without MeHg vs tHg distinction (so the broad tHg label is applied in frontmatter); Cr is similarly treated unspeciated (Cr-VI is not separately tabulated). The review’s nanoparticle-efficacy claims in Table 6 carry percent-reduction ranges (e.g., ZnO-mediated Pb reduction 79–85%) that conflate multiple primary studies and varying experimental conditions; these ranges are useful as orientation but should not be cited as effect-size point estimates. The authors disclose use of OpenAI ChatGPT (GPT-5-mini) for language refinement and grammar correction during manuscript preparation, with full responsibility taken by the authors — this is best-practice disclosure and does not affect the scientific content, but readers should be aware that some prose phrasings may reflect LLM-mediated editing rather than the authors’ native voice. Quantitative dose-response data are largely confined to integer-percent ranges or threshold values rather than concentration-effect curves; the review is unsuitable for any synthesis page that requires effect-size estimates with confidence intervals.

Wiki pages this source may touch

• cadmium
• lead
• arsenic
• nickel
• chromium
• mercury
• remediation-evidence

Verification notes

Existing-page check. DOI grep (10.3390/plants14243834), raw_handle grep (MFK_16-plant-responses-to-heavy-metal-stresses-mechani), and cite-key glob (jarin*) over wiki/sources/ on 2026-06-08 returned no matches. This is a NEW source page — no prior version to merge-enhance. A nearby page ionita2026-plant-responses-mining-heavy-metals.md (the mining-environment-focused review at DOI 10.3390/plants15071045) has overlapping conceptual content (PC/MT detoxification, transporter machinery, signalling cascades) but is a distinct paper with distinct authors, distinct publication year, distinct journal volume/issue, and distinct framing (mining-environment lab-vs-field evidence grading vs Jarin’s nanoparticle-assisted remediation emphasis); the two are listed as near_duplicates: [] because they are conceptually adjacent rather than substantively duplicate.

Evidence tier. B (secondary narrative review without declared search strategy, PRISMA, or risk-of-bias). The paper reports no primary measurements and uses no quantitative meta-analytic pooling; the integer percent-reduction ranges in Table 6 are aggregated from cited primary studies but the review does not specify the aggregation method. A-tier is reserved for primary peer-reviewed studies and authoritative agency monographs; this is a structured narrative integration with substantial coverage of the nanoparticle-remediation literature.

Metals frontmatter. [Cd, Pb, tAs, Ni, Cr, tHg] per the HMTc 10-analyte priority list. Cd is the dominant subject across Tables 2 (six Cd-treatment entries), 3 (two Cd entries), 4 (Cd appears in all five signalling rows), 5 (eleven of thirteen TF rows reference Cd), and 6 (five of seven NP rows reference Cd). Pb is treated in Tables 1 (toxic ≥30 mg kg⁻¹ DW), 2 (Pb-stressed Albizia, Pb-stressed rice), 3 (Pb-stressed rice GR/SOD response), and 6 (ZnO, TiO₂, Fe₃O₄, Se NP-mediated Pb reduction). As is treated in Tables 1 (toxic ≥5 mg kg⁻¹ DW), 4 (As appears in calcium-dependent, MAPK, ROS, hormonal, and crosstalk rows), and 6 (TiO₂ and biogenic Fe-Mn oxides for As remediation); As speciation (arsenite/arsenate) is discussed at the chemical/uptake-pathway level in Section 2 but the toxicity and response framings throughout use unspeciated “As” — the broad tAs label is applied per HMI convention. Ni is treated in Tables 1 (essential micronutrient, toxic >50 mg kg⁻¹ DW), 2 (four Ni entries across rice, wheat, maize, sunflower, pigeon pea), and 5 (sorghum SbMYB15 confers Cd+Ni tolerance). Cr is treated in Tables 1 (toxic ≥5 mg kg⁻¹ DW), 2 (sunflower-Cr), 3 (mung bean APX response), 4 (Cr appears in calcium-dependent, MAPK, hormonal, crosstalk rows), and 6 (ZnO NPs reduced Cr 38–81%, Aspergillus niger TiO₂ NPs reduce Cr(VI) toxicity). Cr-VI is mentioned in the Clostridium pasteurianum (Table 7) Cr(VI) → Cr(III) reduction and in Aspergillus niger TiO₂ NP Cr(VI) DNA-damage reduction but not separately tabulated at the toxicity-threshold level; Cr is the appropriate broad label. Hg is treated in Tables 1 (toxic ≥1 mg kg⁻¹ DW — the lowest threshold in Table 1), 2 (rice canopy/tiller/panicle/yield reduction), 3 (okra SOD/APX/GR increase), and 6 (Se NPs reduce Hg 3–23%); the review does not distinguish MeHg vs tHg, so the broad tHg label is applied per HMI convention. Cu, Fe, Mn, Mo, Zn, Co are discussed substantively (Table 1 ranges, antioxidant responses in Table 3) but are not on HMI’s 10-analyte priority list and are not in frontmatter. Al appears once (Table 6 TiO₂ NPs reduce Pb/As/Al 34–97% in rice/cucumber) — single mention insufficient for substantive frontmatter coverage, omitted per HMI scope discipline.

Ingredients, products, matrices, jurisdictions frontmatter. All empty. The source measures nothing in any food matrix. Plant species named (rice, wheat, maize, sunflower, lentil, pigeon pea, Siris tree, Indian mustard, Silene compacta, Thalpsi ochroleucum, Arabidopsis, duckweed, Albizia lebbeck, Brassica juncea, Lemna minor, mung bean, tomato, okra, Jatropha integerrima, coffee, water hyacinth, camelthorn, sorghum, walnut, rapeseed, fenugreek, Leucaena leucocephala, coriander, pak choi, lettuce) appear as toxicology/transgenic-model/AMF-symbiosis subjects with phytotoxicity endpoints (lipid peroxidation, antioxidant-enzyme activity, biomass reduction), not as sampled food commodities with reported HM concentrations. No national regulatory framework or occurrence dataset is engaged; the institutional affiliations span Bangladesh, USA (Texas), and Vietnam but the review’s framing is conceptually international and does not anchor to any single jurisdictional regulatory regime. jurisdictions: remains empty.

Sample size. Null. The narrative has no sampling frame; the review summarises ~244+ primary and secondary studies but does not aggregate their sample sizes. sample_n represents the latter and is null here.

Brand firewall (Part 12). No commercial food, supplement, personal-care, or NP-product brand names appear in the source body for contamination values. The nanoparticle catalogue in Table 6 names chemical compounds (ZnO, CeO₂, TiO₂, Fe₃O₄, etc.) rather than commercial product brands. The microbial-isolate catalogue in Table 7 names microbial strain genera/species (Pseudomonas aeruginosa, Bacillus subtilis, E. coli, etc.) rather than commercial bioremediation products. No firewall action required.

HMTc firewall (Part 2). The review contains no HMTc-threshold language, no claims about HMI certification levels, and no consumer-audience risk advisories. The Section 8 “Future Research Directions” framing includes forward-looking proposals (CRISPR/Cas9 gene editing of WRKY/MYB/bZIP TFs and HMA3/Nramp transporters; multi-omics integration; ecological-risk assessment of NP fate; field-applicable phytoremediation protocols) — these are research-agenda framings for the plant-biotechnology and phytoremediation communities, not HMTc threshold proposals, and are preserved in the Implications section without escalation. The Table 1 plant-tissue toxic-threshold values (Cd ≥5, Pb ≥30, As ≥5, Cr ≥5, Hg ≥1 mg kg⁻¹ DW) are explicitly labelled in the Implications and Limitations sections as plant-tissue growth-inhibition thresholds rather than human-exposure regulatory ceilings to prevent inadvertent conflation. No firewall action required.

Date arithmetic. Received 29 September 2025, revised 29 November 2025, accepted 9 December 2025, published 16 December 2025 — all consistent with the year: 2025 frontmatter. The journal issue Plants 2025, Vol 14, Article 3834 carries 2025 as the publication year. DOI 10.3390/plants14243834 resolves to Plants 2025, Vol 14, Article 3834.

Reviewer’s note on scope fit. This paper is in the “Black Market Peptide Metal Survey / heavy_metals_peptides” Manual Fetch Kimi folder alongside luo2024-peptides-heavy-metal-remediation, riyazuddin2022-heavy-metal-toxicity-sequestration-plants, marques2025-phytochelatins-cadmium-mitigation, ruttkay-nedecky2013-metallothionein-oxidative-stress, ionita2026-plant-responses-mining-heavy-metals, and the Zhang/Metalorian de novo peptide design paper. Per the 2026-06-02 commit 3f47f95 — scope: mitigation/remediation is in-scope, not a skip, peptide-mediated and phytoremediation papers are in scope as background for the mitigation-evidence chapter. This paper’s distinctive contribution within the folder set is the structured nanoparticle-assisted remediation catalogue (Tables 6, 7) and the integrated TF/signalling-pathway framing (Tables 4, 5); the other peptide-axis papers in the folder are more narrowly focused on specific chelation pathways (Marques on Cd/PC; Ruttkay-Nedecky on mammalian MT/oxidative stress) or general taxonomy (Luo on peptide-metal remediation; Riyazuddin on multi-mechanism plant tolerance; Ionita on mining-environment lab-vs-field evidence grading). The phytochelatin/metallothionein peptide axis — the reason the Kimi agent grouped these papers — is treated in Section 5.2 (PC/MT chelation integration) and Table 5 (HSF, MYB, WRKY, bZIP regulation of MT genes and Cd-tolerance pathways).

Slug-vocabulary note. [[mitigation/remediation-evidence]] exists at wiki/mitigation/remediation-evidence.md. [[metals/cadmium]], [[metals/lead]], [[metals/arsenic]], [[metals/nickel]], [[metals/chromium]], [[metals/mercury]] all exist at corresponding paths under wiki/metals/ (verified by directory listing). No invalid slugs.

Speciation note. The source uses “As”, “Cr”, and “Hg” without consistent speciation. As(III)/arsenite and As(V)/arsenate are distinguished at the chemical-uptake-pathway level in Section 2 (As(III) via aquaporin channels binding sulfhydryl groups; As(V) via phosphate transporters, largely reduced to As(III) in roots) but the toxicity-threshold (Table 1) and antioxidant/signalling responses (Tables 3, 4) use unspeciated “As”. Cr(VI) appears in Table 7 (Clostridium pasteurianum Cr(VI)→Cr(III) reduction, Aspergillus niger Cr(VI) DNA-damage reduction) but the toxicity-threshold (Table 1) uses unspeciated “Cr”. MeHg vs tHg is not distinguished in the source. Per the HMI convention, the broad tAs and tHg labels are applied in frontmatter; Cr is used (Cr-VI is not separately listed); the wiki’s prose preserves the source’s vocabulary verbatim.

ChatGPT-disclosure note. The Acknowledgments section explicitly states: “During the preparation of this manuscript, the authors used OpenAI’s ChatGPT (GPT-5-mini) for the purposes of language refinement and grammar correction of the manuscript text. The authors have reviewed and edited the output and take full responsibility for the content of this publication.” This is best-practice LLM-use disclosure per emerging MDPI and Committee on Publication Ethics guidance; it is noted in the Limitations section but does not affect the evidence-tier classification.

Audit subagent (2026-06-08) verdict: PROMOTE. Five checks (numerical fidelity, slug vocabulary, speciation/methods, brand firewall, HMTc firewall) returned five ✅ with one ⚠️ on a narrative-count discrepancy in the Table 7 prose (“Twenty-one microbial isolate/plant extract entries across seven NP types” — body table actually has 15 rows across 8 NP types). The discrepancy was independently verified against PDF p. 15–16 (4 silver + 3 gold + 2 ZnO + 1 lead + 2 iron + 1 TiO₂ + 1 biogenic Fe-Mn + 1 CdS = 15 rows; eight NP type categories) and the narrative was corrected to “Fifteen microbial isolate/plant extract entries across eight NP types”; the Why-this-matters bullet and the introductory paragraph references to Table 7 counts were corrected from 14 to 15 in parallel. All table data, percent-reduction ranges, and reference attributions were verified faithful to the source by the subagent. All wikilink slugs (metals/cadmium, metals/lead, metals/arsenic, metals/nickel, metals/chromium, metals/mercury, mitigation/remediation-evidence) verified present in the wiki. Brand firewall (Part 12) and HMTc firewall (Part 2) both clean — no commercial brand names, no threshold language, plant-tissue toxic thresholds correctly framed as growth-inhibition thresholds rather than human-exposure regulatory ceilings. 1 finding flagged, 1 correction applied (Table 7 narrative count 21→15 and NP-type count 7→8), 0 rejected. Audit subagent ID a53974aac3bb0c442.

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.