Asgher, Rehaman, Islam, Arshad & Khan 2023 — Selenium-mediated tolerance of plants to heavy-metal stress (narrative review)

This MDPI Agriculture review synthesises laboratory and greenhouse evidence on how exogenous selenium (Se) — applied as selenite (SeO₃²⁻), selenate (SeO₄²⁻), selenocysteine (SeCys), selenomethionine (SeMT), or selenium nanoparticles (SeNPs) — modulates uptake, translocation, antioxidant metabolism, osmolyte production, phytohormone signalling, secondary-metabolite biosynthesis, and mineral-nutrient acquisition in crop and model plants exposed to cadmium, lead, arsenic, chromium, nickel, copper, zinc, aluminium, and mercury. The paper is a narrative review with no independent measurements, no primary data extraction, and no quantitative meta-analysis; quantitative entries in Tables 1–3 are experimental treatment doses and qualitative response statements drawn from cited primary studies rather than occurrence values. It is ingested as an out-of-core-scope agronomic-mitigation-context reference following the bae2018-absorbent-hygiene-pads-safety-review precedent for methodology / context reviews without primary metal-occurrence data; metals: [], ingredients: [], and products: [] are correct because the paper contributes no measured contamination values to any HMI ingredient, product, or metal page. The review is potentially useful as a starting point for an HMI mitigation-lever entry on Se biofortification / Se co-application as an agronomic intervention to reduce heavy-metal accumulation in cereal and vegetable crops, but each specific mechanistic claim should be sourced from its underlying primary citation rather than from this review.

Key numbers

This is a narrative review with no primary measurements. The numerical content consists of (a) bibliometric counts of publications on Se / HM / Se+HM 2010–2022 from Dimensions software, (b) experimental treatment doses of Se and heavy metals tabulated from cited primary studies, and (c) the review’s own qualitative statements about Se concentration thresholds for beneficial vs toxic effects in plants.

Bibliometric framing (Figures 1–2, pages 3–4)

• Search platform: Dimensions software 2.6.0 (https://www.dimensions.ai/). Search terms: “selenium”, “heavy metal stress”, “stress tolerance”, “plant”. Export date: 10 May 2023. Year filter: 2010–2022. Country filter: past eight years.
• Figure 1: publications per year 2010–2022, with separate counts for Se-only, HM-only, and HM+Se. Selected year-totals as reported: 2010 (Se 1, HM 62, HM+Se 2); 2017 (Se 5, HM 164, HM+Se 2); 2021 (Se 19, HM 392, HM+Se 13); 2022 (Se 18, HM 423, HM+Se 28).
• Figure 2: country-wise totals over the past eight years (counts as reported, Se vs HM): USA (Se 62, HM 208), China (Se 53, HM 184), Russia (Se 33, HM 141), Bangladesh (Se 12, HM 85), Pakistan (Se 15, HM 126), India (Se 21, HM 138), Poland (Se 16, HM 59), Others (Se 34, HM 315).

Author-stated Se concentration thresholds for plants (pages 2, 6–7)

• “The low concentration (<1000 mg Se/kg DW) of Se can reduce metals’ toxic effects on plants and develop tolerance against stress by inducing different metabolic processes” (cited to ref [20]).
• “However, at higher concentration (>1000 mg Se/kg DW), Se affects plant growth and decrease the level of organogenesis, nucleic acid synthesis and protein synthesis” (cited to ref [20]).
• “Selenium might be useful for plant growth and development at low concentrations under optimum and unfavorable conditions” (cited to ref [17]); at high doses “it generates ROS and impairs several cellular activities” (cited to ref [99]).

Table 1 — Role of Se under HM stress conditions (page 6)

Treatment doses and qualitative response statements as tabulated by the authors from cited primary studies:

Table 2 — Role of phytohormones under heavy-metal stress (pages 9–10)

Selected entries as tabulated (HM dose / phytohormone dose / response, cited primary reference):

Table 3 — Effect of Se on secondary-metabolite production (pages 12–13)

Author-stated single-point quantitative claims (selected, pages 5–14)

• 2 µM Se “improved root growth and decreased oxidative stress in Al-treated Lolium perenne” (cited to ref [84], page 5 prose). Source-internal discrepancy: Table 1 (page 6) reports the same Lolium perenne / ref [84] entry as 5 µM Se reducing lipid peroxidation under 0.2 µM Al, not 2 µM. The wiki preserves both figures as the review reports them; the underlying primary study (ref [84], Cartes et al. 2010 in Ann. Appl. Biol.) would need to be consulted directly to resolve which dose corresponds to which endpoint.
• 4 µM Se “alleviated Zn stress by improving growth and photosynthesis in Billbergia zebrina” (cited to ref [96], page 6).
• SeMT 3 µM “mitigated Cd toxicity in mustard species by enhancing enzymatic antioxidants and preventing Cd aggregation in cell organelles” (cited to ref [89]).
• Leaf spraying of Se (10, 20, 40 µM) “reduced Cd toxicity by limiting Cd uptake by roots and improved photosynthetic attributes, osmoprotectants and antioxidant levels in Satureja hortensis” (cited to ref [90]).
• Foliar Se in wheat leaves “inhibited metal uptake and enhanced nutritional status of wheat by accumulating more Se in the grains” (cited to ref [38]).

Methods (brief)

Narrative literature review covering 1982–2023. Search platform: Dimensions software 2.6.0; supplementary searches via PubMed, Google Scholar, Science Direct, and Scopus. Authors did not declare a PRISMA protocol, did not report inclusion/exclusion criteria beyond topical relevance to Se / HM / plants, and did not perform quantitative meta-analysis or independent data extraction. Bibliometric counts in Figures 1–2 were generated by Dimensions filters on year (2010–2022) and country (past eight years) for the search terms “selenium”, “heavy metal stress”, “stress tolerance”, and “plant”. Tables 1–3 reproduce treatment doses and qualitative response statements from cited primary studies as the authors interpreted them; concentration values reflect what the original experiments applied to plants rather than measured occurrence in food.

Implications

• Certification (HMTc): This review contributes no occurrence values to any HMTc product-category threshold. It is potentially useful as background reading for an HMTc educational note on agronomic interventions (Se biofortification, Se co-application, SeNP foliar treatments) that have been investigated as ways to reduce heavy-metal accumulation in cereal and leafy-vegetable crops. Any HMTc-side use of the specific mechanistic claims should be traced through this review to the underlying primary references rather than cited from the review itself.
• Courses: Useful as a reference for an educational module on agronomic mitigation levers — covering inorganic Se (selenite, selenate) versus organic Se (SeCys, SeMT) versus SeNP application routes, foliar versus root application trade-offs, dose ranges associated with beneficial versus toxic effects in plants (<1000 mg Se/kg DW beneficial; >1000 mg Se/kg DW toxic, per cited ref [20]), and the cross-talk among Se, phytohormones, osmolytes, and secondary metabolites. The tables provide a starting catalogue of crop / metal / Se-dose / response combinations reported in the primary literature.
• App: Not applicable. No per-product or per-ingredient occurrence values; no consumer-facing exposure estimates.
• Microbiome: Not addressed. Out of scope for microbiome federation.
• Synthesis: No synthesis triggers fire from this ingest. The paper does not contribute primary occurrence values to any ingredient contamination_profile cell.

Wiki pages this source may touch

This is a narrative agronomic-mitigation review; it contributes context rather than primary data. Potential touch points for future synthesis or educational use (not generating routing rows because no occurrence data are reported):

• Mitigation-lever context for cereal ingredient pages where Se biofortification has been studied as an HM uptake-reduction intervention (rice, wheat, maize).
• Mitigation-lever context for Brassica-family ingredient pages (mustard, broccoli, cauliflower, rapeseed).
• Background reference for metals/cadmium, metals/lead, metals/arsenic, metals/chromium, and metals/nickel mitigation sections discussing Se co-application as a phytoremediation / uptake-reduction strategy.
• Reference for any future mitigation/se-biofortification.md or mitigation/se-coapplication.md page.

Verification notes

• No primary occurrence data. metals: [], ingredients: [], and products: [] are correct. Following the bae2018-absorbent-hygiene-pads-safety-review precedent for narrative reviews without primary measurements: this paper reviews laboratory experiments on Se-mediated tolerance mechanisms in plants exposed to heavy metals; it does not report contamination levels in any food ingredient or product. Routing to metal or ingredient pages as direct_evidence would mischaracterise the evidence. The mitigation-lever angle (Se biofortification reducing Cd/Pb/As accumulation in cereal grains) is documented in body text for future discoverability without generating misleading routing rows.
• Speciation discipline. The paper uses “As” throughout without consistently separating inorganic vs total arsenic. Treatment doses in Table 1 (e.g., 25 µM As for Glycine max, 100 µM As for Oryza sativa) are applied to plants as treatment solutions; the speciation of the applied As in the primary studies would need to be checked against each cited reference. The review does not analyse arsenic speciation in plant tissues post-treatment. Similarly, “Cr” in Table 1 (Brassica juncea, 300 µM Cr) and “Hg” mentions in body text do not separate Cr-VI from total Cr or MeHg from tHg. Because this page reports the review’s own framing without overlaying speciation distinctions the authors did not make, metals: [] avoids forcing a speciation choice the source does not support.
• Plant-tissue matrix. matrices: [plant-tissue] reflects that the experiments cited measure HM and Se in plant material (roots, shoots, grains, leaves) under controlled exposure, not in food as consumed.
• Brand-firewall compliance (Part 12). No commercial product or brand names appear in the paper. Methods sections of cited primary studies are not reproduced at instrument-vendor level in this review. No Part 12 concerns.
• Wiki/HMTc firewall (Part 2) compliance. The page reports what the review describes (mechanisms, doses, responses) without proposing HMTc thresholds, endorsing the review’s synthesis claims as wiki consensus, or making consumer-audience risk statements. The “Author-stated Se concentration thresholds for plants” entries quote the review’s framing of <1000 vs >1000 mg Se/kg DW as the beneficial/toxic threshold; this is reported as what the review says, not adopted as wiki claim.
• Evidence tier. Tier B — peer-reviewed narrative review without PRISMA protocol or independent meta-analysis. Per conventions evidence grading, narrative reviews sit below primary peer-reviewed studies (Tier A) but above grey literature; specific claims attributed in tables are no stronger than the underlying primary references they cite.
• Sample-size. sample_n: null is correct for a narrative review; the bibliometric counts in Figures 1–2 (e.g., 423 HM publications in 2022) reflect Dimensions search-result totals, not a defined sample frame for evidence extraction.
• License. MDPI Agriculture publishes under Creative Commons Attribution (CC BY 4.0) license per MDPI’s standard open-access policy. DOI 10.3390/agriculture13051083 resolves to the open-access article.
• Funding statement (page 15): “This research received no external funding.” No conflict-of-interest concerns declared by the authors.
• Audit subagent (2026-06-02) flagged Check 1 ⚠️ on a duplicate Billbergia zebrina / ref [96] bullet (4 µM Se / Zn stress) appearing twice in Author-stated single-point quantitative claims; verified against source page 6 — claim appears once in the source, the duplicate was a wiki-side formatting artifact. Removed the duplicate; one canonical entry retained. Also flagged Check 1 ⚠️ on a source-internal Lolium perenne / ref [84] dose discrepancy (page 5 prose says 2 µM Se, Table 1 row says 5 µM Se for the same primary reference). Verified against source — both numbers are present in the review, attributed to the same primary citation. Added an explicit source-internal-discrepancy flag to the Author-stated bullet preserving both figures rather than silently picking one. Audit’s verdict was REVISE; both findings applied; no other ❌ or ⚠️ findings.

Ingest log

• 2026-06-02 fresh ingest (Claude Opus 4.7, autonomous v2.0 manual-fetch skill, daemon tick): NEW path. Three identity checks against wiki/sources/ returned no hits: DOI 10.3390/agriculture13051083 not present; raw_handle MFK_agriculture-13-01083-v2 not present; cite-key stem asgher2023 not present. PDF SHA-256 c5a2bdd8aaf709da97fc50a2a436722d31ca4ad6f6e039d6274e91cc272de32e. Paper is a narrative review of selenium-mediated plant tolerance to heavy-metal stress; no primary occurrence measurements. Ingested as out-of-core-scope agronomic-mitigation-context reference per the bae2018-absorbent-hygiene-pads-safety-review precedent; metals: [], ingredients: [], products: [] correctly reflect that no contamination values are contributed to any wiki page.

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.