Zinc Hyperaccumulation in Plants: A Review

Enhancing the phytoextraction efficiency of heavy metals in acidic and alkaline soils by Sedum alfredii Hance: A study on the synergistic effect of plant growth regulator and plant growth-promoting bacteria

Plant growth regulators (PGR) and plant growth-promoting bacteria (PGPB) have the potential in phytoremediation of heavy metals (HMs) contaminated soils. However, their sole application may not yield the optimal results, thus necessitating the combined application. The present study aimed to enhance the phytoremediation efficiency of Sedum alfredii Hance (S. alfredii) in acidic and alkaline soils through the combination of PGR (Brassinolide, BR) and PGPB (Pseudomonas fluorescens, P. fluorescens). The combination of BR and P. fluorescens (BRB treatment) effectively increased the removal efficiency of S. alfredii for Cd, Pb, and Zn by 355.2 and 155.3 %, 470.1 and 128.9 %, and 408.4 and 209.6 %, in acidic and alkaline soils, respectively. Moreover, BRB treatment led to a substantial increase in photosynthetic pigments contents and antioxidant enzymes activities, resulting in a remarkable increase in biomass (86.71 and 47.22 %) and dry mass (101.49 and 42.29 %) of plants grown in acidic and alkaline soils, respectively. Similarly, BRB treatment significantly elevated the Cd (109.4 and 71.36 %), Pb (174.9 and 48.03 %), and Zn levels (142.8 and 104.3 %) in S. alfredii shoots, along with cumulative accumulation of Cd (122.7 and 79.47 %), Pb (183.8 and 60.49 %), and Zn (150.7 and 117.9 %), respectively. In addition, the BRB treatment lowered the soil pH and DTPA-HMs contents, while augmenting soil enzymatic activities, thereby contributing soil microecology and facilitating the HMs absorption and translocation by S. alfredii to over-ground tissues. Furthermore, the evaluation of microbial community structure in phyllosphere and rhizosphere after remediation revealed the shift in microbial abundance. The combined treatment altered the principal effects on S. alfredii HMs accumulation from bacterial diversity to the soil HMs availability. In summary, our findings demonstrated that synergistic application of BR and P. fluorescens represents a viable approach to strengthen the phytoextraction efficacy of S. alfredii in varying soils.

Nano zerovalent Fe did not reduce metal(loid) leaching and ecotoxicity further than conventional Fe grit in contrasting smelter impacted soils: A 1-year field study

The majority of the studies on nanoscale zero-valent iron (nZVI) are conducted at a laboratory-scale, while field-scale evidence is scarce. The objective of this study was to compare the metal(loid) immobilization efficiency of selected Fe-based materials under field conditions for a period of one year. Two contrasting metal(loid) (As, Cd, Pb, Zn) enriched soils from a smelter-contaminated area were amended with sulfidized nZVI (S-nZVI) solely or combined with thermally stabilized sewage sludge and compared to amendment with microscale iron grit. In the soil with higher pH (7.5) and organic matter content (TOC = 12.7 %), the application of amendments resulted in a moderate increase in pH and reduced As, Cd, Pb, and Zn leaching after 1-year, with S-nZVI and sludge combined being the most efficient, followed by iron grit and S-nZVI alone. However, the amendments had adverse impacts on microbial biomass quantity, S-nZVI being the least damaging. In the soil with a lower pH (6.0) and organic matter content (TOC = 2.3 %), the results were mixed; 0.01 M CaCl2 extraction data showed only S-nZVI with sludge as remaining effective in reducing extractable concentrations of metals; on the other hand, Cd and Zn concentrations were increased in the extracted soil pore water solutions, in contrast to the two conventional amendments. Despite that, S-nZVI with sludge enhanced the quantity of microbial biomass in this soil. Additional earthworm avoidance data indicated that they generally avoided soil treated with all Fe-based materials, but the presence of sludge impacted their preferences somewhat. In summary, no significant differences between S-nZVI and iron grit were observed for metal(loid) immobilization, though sludge significantly improved the performance of S-nZVI in terms of soil health indicators. Therefore, this study indicates that S-nZVI amendment of soils alone should be avoided, though further field evidence from a broader range of soils is now required.

Physiological response and molecular mechanism of Quercus variabilis under cadmium stress

Heavy metal pollution is a global environmental problem, and Quercus variabilis has a stronger tolerance to Cd stress than do other species. We aimed to explore the physiological response and molecular mechanisms of Q. variabilis to Cd stress. In this study, the antioxidant enzyme activities of leaves were determined, while the photosynthetic parameters of leaves were measured using Handy PEA, and ion fluxes and DEGs in the roots were investigated using noninvasive microtest technology (NMT) and RNA sequencing techniques, respectively. Cd stress at different concentrations and for different durations affected the uptake patterns of Cd2+ and H+ by Q. variabilis and affected the photosynthetic efficiency of leaves. Moreover, there was a positive relationship between antioxidant enzyme (CAT and POD) activity and Cd concentration. Transcriptome analysis revealed that many genes, including genes related to the cell wall, glutathione metabolism, ion uptake and transport, were significantly upregulated in response to cadmium stress in Q. variabilis roots. WGCNA showed that these DEGs could be divided into eight modules. The turquoise and blue modules exhibited the strongest correlations, and the most significantly enriched pathways were the phytohormone signaling pathway and the phenylpropanoid biosynthesis pathway, respectively. These findings suggest that Q. variabilis can bolster plant tolerance by modulating signal transduction and increasing the synthesis of compounds, such as lignin, under Cd stress. In summary, Q. variabilis can adapt to Cd stress by increasing the activity of antioxidant enzymes, and regulating the fluxes of Cd2+ and H+ ions and the expression of Cd stress-related genes.

Nano zinc oxide mediated resuscitation of aged Cajanus cajan via modulating aquaporin, cell cycle regulatory genes and hormonal responses

KEY MESSAGE

Nanoparticle pretreatment improved the health of aged Cajanus cajan seeds viz., regulation of redox status, gene expression, and restoration of hormonal homeostasis. Ageing deteriorates the quality of seeds by lowering their vigor and viability, and terminating with loss of germination. These days, nanotechnology has been seen to revolutionize the agricultural sectors, and particularly nano zinc oxide (nZnO) has gained considerable interests due to its distinctive properties. The aim of the present work was to decipher the possibilities of using nZnO to rejuvenate accelerated aged (AA) seeds of Cajanus cajan. Both chemically (CnZnO) and green (GnZnO; synthesized using Moringa oleifera) fabricated nZnOs were characterized via standard techniques to interpret their purity, size, and shape. Experimental results revealed erratic germination with a decline in viability and membrane stability as outcomes of reactive oxygen intermediate (ROI) buildup in AA seeds. Application of nZnO substantially rebated the accrual of ROI, along with enhanced production of antioxidants, α-amylase activity, total sugar, protein and DNA content. Higher level of zinc was assessed qualitatively/ histologically and quantitatively in nZnO pulsed AA seeds, supporting germination without inducing toxicity. Meantime, augmentation in the gibberellic acid with a simultaneous reduction in the abscisic acid level were noted in nZnO invigorated seeds than that determined in the AA seeds, suggesting possible involvement of ROI in hormonal signalling. Furthermore, nZnO-subjected AA seeds unveiled differential expression of aquaporins and cell cycle regulatory genes. Summarizing, among CnZnO and GnZnO, later one holds better potential for a revival of AA seeds of Cajanus cajan by providing considerable tolerance against ageing-associated deterioration via recouping the cellular redox homeostasis, hormonal signaling, and alteration in expression patterns of aquaporin and cell cycle regulatory genes.

Towards a comprehensive understanding of zinc tolerance in Limonium brasiliense as a useful tool for environmental remediation and monitoring

Heavy metal pollution is a serious environmental problem worldwide, creating the necessity to find eco-friendly strategies for monitoring and remediating environments. This study aimed to evaluate morphological, physiological, and biochemical responses as indicative of Zn tolerance in Limonium brasiliense and to determine the ability of this halophyte to accumulate different concentrations of Zn (0, 100, and 200 μM) in hydroponic conditions. The leaf shape at high Zn concentration showed enlarged petioles and lanceolate blades, whereas the leaf size was reduced. Water content, chlorophyll fluorescence parameters, and pigment content decreased with Zn addition. Of the antioxidant activities, only APx increased 75% compared to the control by Zn stress. Zn concentration was higher in aerial structures than in roots (BAC> 1 and TF> 1), suggesting that L. brasiliense could function as an accumulator of Zn. Its great ability to resist metal stress and its strong capacity to protect itself against high Zn concentration postulate it as a good phytoremediation of environments enriched with Zn. The study emphasizes using leaf morphology as an early biomonitoring tool for detecting Zn pollution, providing more evidence of their potential use as a biomarker for evaluating and assessing ecosystem health in biomonitoring programs.

How plants respond to heavy metal contamination: a narrative review of proteomic studies and phytoremediation applications

MAIN CONCLUSION

Heavy metal pollution caused by human activities is a serious threat to the environment and human health. Plants have evolved sophisticated defence systems to deal with heavy metal stress, with proteins and enzymes serving as critical intercepting agents for heavy metal toxicity reduction. Proteomics continues to be effective in identifying markers associated with stress response and metabolic processes. This review explores the complex interactions between heavy metal pollution and plant physiology, with an emphasis on proteomic and biotechnological perspectives. Over the last century, accelerated industrialization, agriculture activities, energy production, and urbanization have established a constant need for natural resources, resulting in environmental degradation. The widespread buildup of heavy metals in ecosystems as a result of human activity is especially concerning. Although some heavy metals are required by organisms in trace amounts, high concentrations pose serious risks to the ecosystem and human health. As immobile organisms, plants are directly exposed to heavy metal contamination, prompting the development of robust defence mechanisms. Proteomics has been used to understand how plants react to heavy metal stress. The development of proteomic techniques offers promising opportunities to improve plant tolerance to toxicity from heavy metals. Additionally, there is substantial scope for phytoremediation, a sustainable method that uses plants to extract, sequester, or eliminate contaminants in the context of changes in protein expression and total protein behaviour. Changes in proteins and enzymatic activities have been highlighted to illuminate the complex effects of heavy metal pollution on plant metabolism, and how proteomic research has revealed the plant's ability to mitigate heavy metal toxicity by intercepting vital nutrients, organic substances, and/or microorganisms.

Sustained release of Zn from zinc sulfide nanoparticles (ZnS NPs) amplified the bioaccessibility of Zn in soil: Adsorption dynamics and dissolution kinetics

Controlled-release micronutrient supplementation to provide better bioavailable zinc (Zn) under alkaline soil conditions is a concept of commercial pertinence for sustainable agriculture. High pH stable nano-scaled ZnS is the material under study in the present investigation where the adsorption dynamics and dissolution kinetics of sono-chemically synthesized zinc sulfide nanoparticles (ZnS NPs) were evaluated in comparison to ZnSO4 in Lufa 2.2 soil for supplementation of Zn. The mechanism of adsorption of ZnS NPs and ZnSO4 onto Lufa 2.2 soil was well explained by fitting into the Freundlich adsorption model and pseudo-second order equation. ZnS NPs reflected the stronger ability to get adsorbed on the Lufa 2.2 soil as compared to metal ions, due to higher surface reactivity of NPs and higher Kf value (0.557) than ZnSO4 (0.463). Time relevant enhancement in extractability of Zn from ZnS NPs amended soil and diminution in extractability of Zn from ZnSO4 spiked soil was observed in bioavailability studies. The increased labile pool of Zn from ZnS NPs amended soil over time was due to their slow dissolution in soil and could be adjusted to consider as "sustained released ZnS NPs". Dissolution of ZnS nanoparticles (NPs) in Lufa 2.2 soil adhered to the first-order extraction model, exhibiting extended half-lives of 27.72 days (low dose) and 28.87 days (high dose). This supported prolonged stability, increased reactivity, and reduced ecological risk compared to conventional Zn salt fertilizers, promoting enhanced crop productivity.

Combined effect of endophytic Bacillus mycoides and rock phosphate on the amelioration of heavy metal stress in wheat plants

BACKGROUND

Zinc (Zn) and nickel (Ni) are nutrients that are crucial for plant growth; however, when they are present at higher concentrations, they can cause toxicity in plants. The present study aimed to isolate plant growth promoting endophytic bacteria from Viburnum grandiflorum and assess its plant and defense promoting potential alone and in combination with RP in zinc (Zn) and nickel (Ni) toxic soil. The isolated endophytic bacteria were identified using 16s rRNA gene sequencing. For the experiment, twelve different treatments were applied using Zn, Ni, isolated endophytic Bacillus mycoides (Accession # MW979613), and rock phosphate (RP). The Ni, Zn and RP were used at the rate of (100 mg/kg) and (0.2 g/kg) respectively. A pot experiment with three replicates of each treatment was conducted using a complete randomized design (CRD).

RESULTS

The results indicated that Ni (T5 = seed + 100 mg/kg Ni and T9 = seed + 100 mg/kg Zn) and Zn concentrations inhibited plant growth, but the intensity of growth inhibition was higher in Ni-contaminated soil. Bacillus mycoides and RP at 100 mg/Kg Zn (T12 = inoculated seed + 100 mg/kg Zn + RP0.2 g/kg.) increased the shoot length, leaf width, protein and sugar content by 57%, 13%, 20% and 34%, respectively, compared to the control. The antioxidant enzymes superoxide dismutases (SOD), peroxidase (POD) were decreased in contaminated soil. Furthermore, Ni and Zn accumulation was inhibited in T11 (seed + 100 mg/kg Zn + RP0.2 g/Kg) and T12 (inoculated seed + 100 mg/kg Zn + RP0.2 g/Kg) by 62 and 63% respectively. The Cu, Ca, and K, contents increased by 128, 219 and 85, Mn, Na, and K by 326, 449, and 84% in (T3 = inoculated seed) and (T4 = inoculated seed + RP 0.2 g/Kg) respectively.

CONCLUSIONS

Ni was more toxic to plants than Zn, but endophytic bacteria isolated from Viburnum grandiflorum, helped wheat (Triticum aestivum) plants and reduced the toxic effects of Ni and Zn. The effect of Bacillus mycoides was more prominent in combination with RP which promoted and suppressed heavy-metal toxicity. The reported combination of Bacillus mycoides and RP may be useful for improving plant growth and overcoming metal stress.

Assessing phytotoxicity and tolerance levels of ZnO nanoparticles on Raphanus sativus: implications for widespread adoptions

The escalating release of zinc oxide nanoparticles (ZnO NPs) into the environment poses a substantial threat, potentially leading to increased concentrations of zinc (Zn) in the soil and subsequent phytotoxic effects. This study aimed to assess the effects of ZnO NPs on Raphanus sativus (R. sativus) concerning its tolerance levels, toxicity, and accumulation. ZnO NPs were synthesized by the wet chemical method and characterized by powder X-ray diffraction (PXRD), Fourier-transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, dynamic light scattering (DLS), and scanning electron microscopy (SEM). The effect of ZnO NPs (70 nm) on R. sativus grown in coir was evaluated. The application of 1,000 mg/L of ZnO NPs resulted in a significant increase (p < 0.05) in soluble protein content, carbohydrates, chlorophyll a (Chl-a), chlorophyll b (Chl-b), total chlorophylls, carotenoids, and antioxidants by 24.7%, 58.5%, 38.0%, 42.2%, 39.9%, 11.2%, and 7.7%, respectively. Interestingly, this dose had no impact on the indole acetic acid (IAA) content. Conversely, the use of 2,000 mg/L of ZnO NPs in the same medium led to a significant reduction (p < 0.05) in soluble protein content by 23.1%, accompanied by a notable increase in IAA by 31.1%, indicating potential toxicity. The use of atomic absorption spectroscopy confirmed the internalization of zinc in seedlings, with a statistically significant increase (p < 0.05). In control plants without ZnO NPs, Zn concentration was 0.36 mg/g, while at the highest ZnO NPs tested dose of 10,000 mg/L, it significantly rose to 1.76 mg/g, causing leaf chlorosis and stunted seedling growth. This suggests potential health risks related to Zn toxicity for consumers. Given the adverse effects on R. sativus at concentrations above 1000 mg/L, caution is advised in the application and release of ZnO NPs, highlighting the importance of responsible practices to mitigate harm to plant life and consumer health. The study demonstrated the tolerance of R. sativus to high Zn levels, classifying it as a Zn-tolerant species.

Novel α-amino acid-like structure decorated biochar for heavy metal remediation in acid soil

Neither chemical nor physical adsorption play well in heavy metals remediation in acid soil due to the competing behavior of abundant protons, where stable chelators that can be reused are of significant demand. Herein, biochar with abundant nitro and carboxyl groups is prepared, which can be assembled into self-supporting electrode. Under the catalyzation of electricity, the surface decorated -NO2 on the biochar can be in situ transformed into -NH2. Combined with the carboxyl group that attached on the same carbon atom, a special α-amino acid-like structure modified biochar (α-AC@BC) can be successfully constructed. Due to the strong affinity between the α-amino acid-like ligand and heavy metals, this α-AC@BC exhibits high removal efficiencies of 83.41%, 80.94%, 92.54% and 77.05% for available copper, cadmium, lead and zinc respectively, even in a strong acid soil with low pH of 4. After four adsorption-desorption cycles, the α-AC@BC could still eliminate 83.88% of copper. The high adsorption energy among -NH2, -COOH and heavy metals (-2.99 eV for copper, -1.90 eV for lead, -1.30 eV for zinc and -0.91 eV for cadmium) could form steady coordination structure to guarantee a highly practical application potential of α-AC@BC in strong acid soil. This study provides a novel concept for the decontamination of multiple heavy metal polluted acid soil.

Ecophysiological response of Populus alba L. to multiple stress factors during the revitalisation of coal fly ash lagoons at different stages of weathering

The enormous quantities of fly ash (FA) produced by thermal power plants is a global problem and safe, sustainable approaches to reduce the amount and its toxic effects are still being sought. Vegetation cover comprising long-living species can help reduce FA dump-related environmental health issues. However, the synergistic effect of multiple abiotic factors, like drought, low organic matter content, a deficit of essential nutrients, alkaline pH, and phytotoxicity due to high potentially toxic element (PTE) and soluble salt content, limits the number of species that can grow under such stressful conditions. Thus, we hypothesised that Populus alba L., which spontaneously colonised two FA disposal lagoons at the 'Nikola Tesla A' thermal power plant (Obrenovac, Serbia) 3 years (L3) and 11 years (L11) ago, has high restoration potential thanks to its stress tolerance. We analysed the basic physical and chemical properties of FA at different weathering stages, while the ecophysiological response of P. alba to multiple stresses was determined through biological indicators [the bioconcentration factor (BCF) and translocation factor (TF) for PTEs (As, B, Cr, Cu, Mn, Ni, Se, and Zn)] and by measuring the following parameters: photosynthetic efficiency and chlorophyll concentration, non-enzymatic antioxidant defence (carotenoids, anthocyanins, and phenols), oxidative stress (malondialdehyde (MDA) concentrations), and total antioxidant capacity (IC50) to neutralise DPPH free radical activity. Unlike at L3, toxic As, B, and Zn concentrations in leaves induced oxidative stress in P. alba at L11, shown by the higher MDA levels, lower vitality, and reduced synthesis of chlorophyll, carotenoids, and total antioxidant activity, suggesting its stress tolerance decreases with long-term exposure to adverse abiotic factors. Although P. alba is a fast-growing species with good metal accumulation ability and high stress tolerance, it has poor stabilisation potential for substrates with high As and B concentrations, making it highly unsuitable for revitalising such habitats.

Zinc induced regulation of PCR1 gene for cadmium stress resistance in rice roots

In this study, the interaction between zinc (Zn) and cadmium (Cd) was investigated in rice roots to evaluate how Zn can protect the plants from Cd stress. Rice seedlings were treated with Cd (100 μM) and Zn (100 μM) in different combinations (Cd alone, Zn alone, Zn+ Cd, Zn+ Cd+ L-NAME, Zn+ Cd+ L-NAME+ SNP). Rice roots treated with only Zn also displayed similar toxic effects, however when combined with Cd exhibited improved growth. Treating the plant with Zn along with Cd distinctly reduced Cd concentration in roots while increasing its own accumulation due to modulation in expression of Zinc-Regulated Transporter (ZRT)-/IRT-Like Protein (OsZIP1) and Plant Cadmium Resistance1 (OsPCR1). Cd reduced plant biomass, cell viability, pigments, photosynthesis and causing oxidative stress due to inhibition in ascorbate-glutathione cycle. L-NAME (NG-nitro L-arginine methyl ester), prominently suppressed the beneficial impacts of Zn against Cd stress, whereas the presence of a NO donor, sodium nitroprusside (SNP), significantly reversed this effect of L-NAME. Collectively, results point that NO signalling is essential for Zn- mediated cross-tolerance against Cd stress via by modulating uptake of Cd and Zn and expression of OsZIP1 and OsPCR1, and ROS homeostasis due to fine tuning of ascorbate-glutathione cycle which finally lessened oxidative stress in rice roots. The results of this study can be utilized to develop new varieties of rice through genetic modifications which will be of great significance for maintaining crop productivity in Cd-contaminated areas throughout the world.

Screening of tolerance of Atriplex vulgatissima under zinc or lead experimental conditions. An integrative perspective by using the integrated biological response index (IBRv2)

The search for plants with a high capacity to tolerate and accumulate metals is an important issue in phytoremediation. In this sense, this study was conducted in the halophyte Atriplex vulgatissima to evaluate the effects of different concentrations of lead (Pb, 50 and 100 μM) or zinc (Zn, 100 and 200 μM) on morphological, physiological, and biochemical parameters as well as the accumulation patterns of this species. The results indicated that while essential metal Zn showed high translocation from roots to shoots (TF > 1), non-essential Pb was mainly accumulated in the roots (BCF>1). Regarding shape, both metals induced slenderness of the blade, but only Zn treatment reduced leaf size. No difference in biomass production and photosynthetic parameters was found between Pb and Zn treatments. Pb treatments did not show significant differences between treatments regarding water content (WC), pigment concentration, and the activity of superoxide dismutase (SOD) and guaiacol peroxidase (GPx), but did result in a decrease in catalase activity at 100 μM Pb. On the other hand, 200 μM Zn leads to a clear reduction in WC and pigment concentrations, along with an increase in SOD and GPx activities. In addition, ascorbate peroxidase (APx) activity showed a hormesis effect at 50 μM Pb and 100 μM Zn. Malondialdehyde increased with both Pb and Zn treatments. The integrated biological index (IBRv2) indicated that 200 μM Zn was the most affected treatment (IBRv2 = 19.02) and that under the same concentrations of metals (100 μM Pb or Zn), Pb treatments presented major stress (IBRv2 = 11.55). A. vulgatissima is a metallophyte with the potential for Pb phytostabilization and Zn phytoextraction, as well as a bioindicator of these metals. Its high biomass and deep roots, combined with its halophytic traits, make it suitable for bioremediation and monitoring programs.

Zinc and nano zinc mediated alleviation of heavy metals and metalloids in plants: an overview

Heavy metals and metalloids (HMs) contamination in the environment has heightened recently due to increasing global concern for food safety and human livability. Zinc (Zn2+ ) is an important nutrient required for the normal development of plants. It is an essential cofactor for the vital enzymes involved in various biological mechanisms of plants. Interestingly, Zn2+ has an additional role in the detoxification of HMs in plants due to its unique biochemical-mediating role in several soil and plant processes. During any exposure to high levels of HMs, the application of Zn2+ would confer greater plant resilience by decreasing oxidative stress, maintaining uptake of nutrients, photosynthesis productivity and optimising osmolytes concentration. Zn2+ also has an important role in ameliorating HMs toxicity by regulating metal uptake through the expression of certain metal transporter genes, targeted chelation and translocation from roots to shoots. This review examined the vital roles of Zn2+ and nano Zn in plants and described their involvement in alleviating HMs toxicity in plants. Moving forward, a broad understanding of uptake, transport, signalling and tolerance mechanisms of Zn2+ /zinc and its nanoparticles in alleviating HMs toxicity of plants will be the first step towards a wider incorporation of Zn2+ into agricultural practices.

Zinc Oxide Nanoparticles Affect Early Seedlings' Growth and Polar Metabolite Profiles of Pea (Pisum sativum L.) and Wheat (Triticum aestivum L.)

The growing interest in the use of zinc oxide nanoparticles (ZnO NPs) in agriculture creates a risk of soil contamination with ZnO NPs, which can lead to phytotoxic effects on germinating seeds and seedlings. In the present study, the susceptibility of germinating seeds/seedlings of pea and wheat to ZnO NPs of various sizes (≤50 and ≤100 nm) applied at concentrations in the range of 100-1000 mg/L was compared. Changes in metabolic profiles in seedlings were analyzed by GC and GC-MS methods. The size-dependent harmful effect of ZnO NPs on the seedling's growth was revealed. The more toxic ZnO NPs (50 nm) at the lowest concentration (100 mg/L) caused a 2-fold decrease in the length of the wheat roots. In peas, the root elongation was slowed down by 20-30% only at 1000 mg/L ZnO NPs. The metabolic response to ZnO NPs, common for all tested cultivars of pea and wheat, was a significant increase in sucrose (in roots and shoots) and GABA (in roots). In pea seedlings, an increased content of metabolites involved in the aspartate-glutamate pathway and the TCA cycle (citrate, malate) was found, while in wheat, the content of total amino acids (in all tissues) and malate (in roots) decreased. Moreover, a decrease in products of starch hydrolysis (maltose and glucose) in wheat endosperm indicates the disturbances in starch mobilization.

Effects of sulfate on the photosynthetic physiology characteristics of Hydrocotyle vulgaris under zinc stress

The effects of sulfate on the zinc (Zn) bioaccumulation characteristics and photophysiological mechanisms of the ornamental plant Hydrocotyle vulgaris were explored using a hydroponic culture under three Zn concentrations (300, 500 and 700mgL-1 ) with (400μmolL-1 ) or without the addition of sulfate. Results showed that: (1) tissue Zn concentrations and total Zn contents increased with increasing hydroponic culture Zn concentrations; and sulfate addition decreased Zn uptake and translocation from roots to shoots; (2) Zn exposure decreased photosynthetic pigment synthesis, while sulfate changed this phenomenon, especially for chlorophyll a under 300mgL-1 Zn treatment; (3) Zn exposure decreased photosynthetic function, while sulfate had positive effects, especially on the photosynthetic rate (Pn ) and stomatal conductance (Gs ); and (4) chlorophyll fluorescence parameters related to light energy capture, transfer and assimilation were generally downregulated under Zn stress, while sulfate had a positive effect on these processes. Furthermore, compared to photosynthetic pigment synthesis and photosynthesis, chlorophyll fluorescence was more responsive, especially under 300mgL-1 Zn treatment with sulfate addition. In general, Zn stress affected photophysiological processes at different levels, while sulfate decreased Zn uptake, translocation, and bioaccumulation and showed a positive function in alleviating Zn stress, ultimately resulting in plant growth promotion. All of these results provide a theoretical reference for combining H. vulgaris with sulfate application in the bioremediation of Zn-contaminated environments at the photophysiological level.

Combined effect of trehalose and spermidine to alleviate zinc toxicity in Vigna radiata

Zinc toxicity is affecting the growth and yield of major crops plants throughout globe by reducing key metabolic processes. In this backdrop, experiments were conducted to evaluate the influence of exogenous supplementation of trehalose (500 µM Treh) and spermidine (500 µM Spd) in alleviating the damaging effects of zinc toxicity (100 µM ZnSO4) in Vigna radiata. Growth, chlorophyll and photosynthesis were reduced due to Zn toxicity; however, exogenous supplementation of trehalose and spermidine not only increased the parameters but also alleviated the decline to considerable levels. Toxicity of zinc increased H2O2, lipid peroxidation and electrolyte leakage by 100.43%, 84.53% and 134.64%, respectively, and application of trehalose and spermidine a reduction of 29.32%, 39.09% and 44.91%, respectively, over the zinc-treated plants. Application of trehalose and spermidine increased the activity of nitrate reductase and the content of nitrogen concomitant with alleviation of the decline caused due to zinc toxicity. The activity of antioxidant system enzymes superoxide dismutase, catalase and the enzymes of ascorbate-glutathione cycle was significantly enhanced due to trehalose and spermidine application. Proline, glycine betaine and activity of γ-glutamyl kinase increased maximally by 281.84%, 126.21% and 181.08%, respectively, in plants treated with zinc + trehalose + spermidine over control. Significant enhancement in the content of total phenols and flavonoids was observed due to the treatment of trehalose and spermidine individually as well as combinedly. Application of trehalose and spermidine reduced the content of methylglyoxal by up-regulating the activity of glyoxylase cycle enzymes. In addition under zinc toxicity conditions, the content of zinc declined in trehalose- and spermidine-treated plants.

The beneficial effects of bare and CMC-supported α-FeOOH, Fe3O4, and α-Fe2O3 nanoparticles on growth, nutrient content, and essential oil of summer savory (Satureja hortensis L.) under Cd, Pb and Zn stresses

This research studies the impacts of iron oxide nanoparticles (FeONPs) on alleviating the toxic effects of cadmium (Cd), lead (Pb), and zinc (Zn) on summer savory (Satureja hortensis L.). Different types of soil additives, including bare and carboxymethylcellulose (CMC)-supported hematite (α-Fe₂O₃), goethite (α-FeOOH), and magnetite (Fe₃O₄), were applied at three rates (0, 0.25, and 0.5% w/w) to a Cd, Pb, and Zn-contaminated soil sample. The experimental results showed that the application of FeONPs increased plant height, dry weights of shoot and root, and yield and content of essential oil. Bare and CMC-supported FeONPs increased the content of K, P, and Fe in the aerial parts of summer savory. However, these soil additives reduced the contents of Cd, Pb, and Zn in plant tissues. CMC-supported FeONPs proved to be more efficient additives in diminishing the toxic effects of Cd, Pb, and Zn in summer savory compared to their bare forms. Bare and CMC-supported goethite NPs were able to restrict the uptake of Cd, Pb, and Zn by summer savory roots in the metal-contaminated soil. The application of CMC-supported goethite at an application dose of 0.5% (w/w) increased shoot dry weight, shoot concentrations of K, P, and Fe, and yield of essential oil by about 62.6, 76.6, 77.1, 210, and 230%, respectively. Conversely, they reduced shoot concentrations of Cd, Pb, and Zn by about 64.6, 68.7, and 40.6%, respectively, compared to the control. These are significant results and indicate that CMC-supported goethite is likely to be the most effective soil additive in diminishing the toxicity of Cd, Pb, and Zn to metal-stressed summer savory.

Dynamic characteristics of heavy metal accumulation in agricultural soils after continuous organic fertilizer application: Field-scale monitoring

Manure has been considered as a source of soil heavy metal (HM) pollution. However, the long-term impact of manure application on soil HM accumulation have not been well studied. This study tracked the long-term cumulative trends of soil copper (Cu), zinc (Zn), arsenic (As), and lead (Pb) in three soil-crop systems over 5-8 years' application of commercial manure fertilizer. The contribution of different fertilization treatments (CF, chemical fertilizer; T1-T3, manure with different application dosages) to soil HMs pollution risk were assessed. There are accumulating tendencies for Cu, Zn, and Pb in paddy fields, Cu and As in orchard fields, and Zn, As, and Pb in vegetable fields, while the concentrations of As in paddy fields and Zn in orchard fields decreased over time. Manure application significantly influenced the accumulation of Cu, Zn, and As in soils rather than that of Pb. The modeling prediction subsequently revealed that the time required to reach the risk screening values (Cu: 50 mg kg^-1; Zn: 200 mg kg^-1) for HM content in paddy soil, according to GB15618-2018, decreased from 18.20 years to 7.20 years due to the introduction of Cu and Zn via manure use. Recommend annual manure application dosage was 7.73 t hm^-2 y^-1 to ensure a 20-year period of clean production in paddy soils, while it was 26.15 t hm^-2 y^-1 in the orchard soil and 16.23 t hm^-2 y^-1 in vegetable soil to ensure a 50-year period of clean production, respectively. Overall, the impacts of HMs input by manure application on soil HMs accumulation varied depending on the type of metal and the soil-crop system. The cumulative trends of HMs in soils play a crucial role in determining whether the input of HMs through manure application can lead to the risk of HM pollution.

Effect of titanium dioxide nanoparticles and co-composted biochar on growth and Cd uptake by wheat plants: A field study

Cadmium (Cd) is a common toxic trace element found in agricultural soils which is due to anthropogenic activities. Cadmium posed a significant risk to humans all around the world due to its cancer-causing ability. The current study demonstrated the effects of soil-applied biochar (BC) and foliar-applied titanium dioxide nanoparticles (TiO₂ NPs) (at a rate of 0.5% and 75 mg/L respectively) alone or in combination on growth and Cd accumulation in wheat plants under field experiment. Soil applied BC and foliar TiO₂ NPs, as well as BC coupled with TiO₂ NPs, reduced Cd contents in grains by 32%, 47%, and 79%, than control respectively. The usage of NPs and BC boosted the plant height as well as chlorophyll contents by lowering oxidative injury and changing antioxidant enzyme activities than control plants. The combined use of NPs and BC prevented excess Cd accumulation in grains over the critical level (0.2 mg/kg) for cereals. The health risk index (HRI) due to Cd was reduced by 79% by co-composted BC + TiO₂ NPs treatment than control. Although, HRI was lower than one for all treatments but this may exceed the limit if grains obtained from such field consumed over long periods. In conclusion, TiO₂ NPs and BC amendments can be implemented in fields across the globe where excess Cd is present soils. Additional studies on the use of such approaches in more precise experimental settings are needed in order to address this environmental problem at larger scale.

Plant-minerals-water interactions: An investigation on Juncus acutus exposed to different Zn sources

Juncus acutus has been proposed as a suitable species for the design of phytoremediation plans. This research aimed to investigate the role played by rhizosphere minerals and water composition on Zn transformations and dynamics in the rhizosphere-plant system of J. acutus exposed to different Zn sources. Rhizobox experiments were conducted using three different growing substrates (Zn from 137 to 20,400 mg/kg), and two irrigation lines (Zn 0.05 and 180 mg/l). The plant growth was affected by the substrate type, whereas the Zn content in the water did not significantly influence the plant height for a specific substrate. J. acutus accumulated Zn mainly in roots (up to 10,000 mg/kg dw); the metal supply by the water led to variable increases in the total Zn concentration in the vegetal organs, and different Zn distributions both controlled by the rhizosphere mineral composition. Different Zn complexation mechanisms were observed, mainly driven by cysteine and citrate compounds, whose amount increased linearly with Zn content in water, but differently for each of the investigated systems. Our study contributes to gain a more complete picture of the Zn pathway in the rhizosphere-plant system of J. acutus. We demonstrated that this vegetal species is not only capable of developing site-specific tolerance mechanisms, but it is also capable to differently modulate Zn transformation when Zn is additionally supplied by watering. These findings are necessary for predicting the fate of Zn during phytoremediation of sites characterized by specific mineralogical properties and subject to water chemical variations.

Seed Priming with Triacontanol Alleviates Lead Stress in Phaseolus vulgaris L. (Common Bean) through Improving Nutritional Orchestration and Morpho-Physiological Characteristics

Worldwide, crop productivity is highly influenced by heavy metal toxicity. Lead (Pb) the is second-most toxic heavy metal that has high persistence in soil. Lead is translocated in plants from rhizosphere soil and enters the food chain, where it poses a significant hazard to the health of humans. In the present investigation, seed priming with triacontanol (Tria) was used to mitigate Pb phytotoxicity in Phaseolus vulgaris L. (common bean). Seeds were primed with different concentrations of Tria (control, 10 µmol L^-1, 20 µmol L^-1, 30 µmol L^-1) solutions. The pot experiment was carried out by sowing Tria-primed seeds in contaminated soil with 400 mg kg^-1 Pb. Lead alone induced a decrease in the rate of germination and a significant reduction in biomass and growth of P. vulgaris as compared to the control. All these negative effects were reversed by Tria-primed seeds. Proliferation of photosynthetic pigments was observed 1.8-fold by Tria under Pb stress. Primed seeds with 20 µmol L^-1 Tria enhanced stomatal conductance (gs), photosynthetic rate (A), transpiration rate (Ei), and uptake of mineral contents (Mg⁺², Zn⁺², Na⁺, and K⁺) and reduced Pb accumulation in seedlings. Tria caused a 1.3-fold increase in osmotic regulator proline synthesis to alleviate Pb stress. Phenolics, soluble protein, and DPPH free radical scavenging activity were enhanced by Tria application, suggesting that exogenous Tria could be employed to improve plant tolerance to Pb stress.

Joint effects of gamma radiation and zinc on duckweed Lemna minor L

When assessing the consequences of combined chemical and radiation pollution on bodies of water, it is important to take into account the interaction of different factors, especially the possible synergistic increase in the toxic effect on growth, biochemical and physiological processes of living organisms. In this work, we studied the combined effect of γ-radiation and zinc on freshwater duckweed Lemna minor L. Irradiated plants (doses were 18, 42, and 63 Gy) were placed on a medium with an excess of zinc (3.15, 6.3, 12.6 μmol/L) for 7 days. Our results showed that the accumulation of zinc in tissues increased in irradiated plants when compared to non-irradiated plants. The interaction of factors in assessing their effect on the growth rate of plants was most often additive, but there was also a synergistic increase in the toxic effect at a zinc concentration of 12.6 μmol/L and irradiation at doses of 42 and 63 Gy. When comparing the combined and separate effects of gamma radiation and zinc, it was found that a reduction in the area of fronds (leaf-like plates) was caused exclusively due to the effects of radiation. Zinc and γ-radiation contributed to the enhancement of membrane lipid peroxidation. Irradiation stimulated the production of chlorophylls a and b, as well as carotenoids.

Biofortification of common bean (Phaseolus vulgaris L.) with iron and zinc: Achievements and challenges

Micronutrient deficiencies (hidden hunger), particularly in iron (Fe) and zinc (Zn), remain one of the most serious public health challenges, affecting more than three billion people globally. A number of strategies are used to ameliorate the problem of micronutrient deficiencies and to improve the nutritional profile of food products. These include (i) dietary diversification, (ii) industrial food fortification and supplements, (iii) agronomic approaches including soil mineral fertilisation, bioinoculants and crop rotations, and (iv) biofortification through the implementation of biotechnology including gene editing and plant breeding. These efforts must consider the dietary patterns and culinary preferences of the consumer and stakeholder acceptance of new biofortified varieties. Deficiencies in Zn and Fe are often linked to the poor nutritional status of agricultural soils, resulting in low amounts and/or poor availability of these nutrients in staple food crops such as common bean. This review describes the genes and processes associated with Fe and Zn accumulation in common bean, a significant food source in Africa that plays an important role in nutritional security. We discuss the conventional plant breeding, transgenic and gene editing approaches that are being deployed to improve Fe and Zn accumulation in beans. We also consider the requirements of successful bean biofortification programmes, highlighting gaps in current knowledge, possible solutions and future perspectives.

Phytoremediation potential of Solanum viarum Dunal and functional aspects of their capitate glandular trichomes in lead, cadmium, and zinc detoxification

In the present scenario, remediation of heavy metals (HMs) contaminated soil has become an important work to be done for the well-being of human and their environment. Phytoremediation can be regarded as an excellent method in environmental technologies. The present contemporary research explores the Solanum viarum Dunal function as a potential accumulator of hazardous HMs viz. lead (Pb), cadmium (Cd), zinc (Zn), and their combination (CHM). On toxic concentrations of Pb, Cd, Zn, and their synergistic exposure, seeds had better germination percentage and their 90d old aerial tissues accumulated Pb, Cd, and Zn concentrations ranging from 44.53, 84.06, and 147.29 mg kg^-1 DW, respectively. Pattern of accumulation in roots was as Zn 70.08 > Pb 48.55 > Cd 42.21 mg kg^-1DW. Under HMs treatment, positive modulation in physiological performances, antioxidant activities suggested an enhanced tolerance along with higher membrane stability due to increased levels of lignin, proline, and sugar. Phenotypic variations were recorded in prickles and roots of 120 d old HM stressed plants, which are directly correlated with better acclimation. Interestingly, trichomes of the plant also showed HM accumulation. Later, SEM-EDX microanalysis suggested involvement of S. viarum capitate glandular trichomes as excretory organs for Cd and Zn. Thus, the present study provides an understanding of the mechanism that makes S. viarum to function as potent accumulator and provides information to generate plants to be used for phytoremediation.

Zinc biofortification through seed nutri-priming using alternative zinc sources and concentration levels in pea and sunflower microgreens

Micronutrient deficiencies caused by malnutrition and hidden hunger are a growing concern worldwide, exacerbated by climate change, COVID-19, and conflicts. A potentially sustainable way to mitigate such challenges is the production of nutrient-dense crops through agronomic biofortification techniques. Among several potential target crops, microgreens are considered suitable for mineral biofortification because of their short growth cycle, high content of nutrients, and low level of anti-nutritional factors. A study was conducted to evaluate the potential of zinc (Zn) biofortification of pea and sunflower microgreens via seed nutri-priming, examining the effect of different Zn sources (Zn sulfate, Zn-EDTA, and Zn oxide nanoparticles) and concentrations (0, 25, 50, 100, and 200 ppm) on microgreen yield components; mineral content; phytochemical constituents such as total chlorophyll, carotenoids, flavonoids, anthocyanin, and total phenolic compounds; antioxidant activity; and antinutrient factors like phytic acid. Treatments were arranged in a completely randomized factorial block design with three replications. Seed soaked in a 200 ppm ZnSO₄ solution resulted in higher Zn accumulation in both peas (126.1%) and sunflower microgreens (229.8%). However, an antagonistic effect on the accumulation of other micronutrients (Fe, Mn, and Cu) was seen only in pea microgreens. Even at high concentrations, seed soaking in Zn-EDTA did not effectively accumulate Zn in both microgreens' species. ZnO increased the chlorophyll, total phenols, and antioxidant activities compared to Zn-EDTA. Seed soaking in ZnSO₄ and ZnO solutions at higher concentrations resulted in a lower phytic acid/Zn molar ratio, suggesting the higher bioaccessibility of the biofortified Zn in both pea and sunflower microgreens. These results suggest that seed nutrient priming is feasible for enriching pea and sunflower microgreens with Zn. The most effective Zn source was ZnSO₄, followed by ZnO. The optimal concentration of Zn fertilizer solution should be selected based on fertilizer source, target species, and desired Zn-enrichment level.

Assisted Phytostabilization of Mine-Tailings with Prosopis laevigata (Fabaceae) and Biochar

Phytoremediation is a cost-effective technique to remediate heavy metal (HM) polluted sites. However, the toxic effects of HM can limit plant establishment and development, reducing phytoremediation effectiveness. Therefore, the addition of organic amendments to mine wastes, such as biochar, improves the establishment of plants and reduces the bioavailability of toxic HM and its subsequent absorption by plants. Prosopis laevigata can establish naturally in mine tailings and accumulate different HM; however, these individuals show morphological and genetic damage. In this study, the effect of biochar on HM bioaccumulation in roots and aerial tissues, HM translocation, morphological characters and plant growth were evaluated, after three and six months of exposure. Plants grown on mine tailings with biochar presented significantly higher values for most of the evaluated characters, in respect to plants that grew on mine tailing substrate. Biochar addition reduced the bioaccumulation and translocation of Cu, Pb, and Cd, while it favored the translocation of essential metals such as Fe and Mn. The addition of biochar from agro-industrial residues to mine tailings improves the establishment of plants with potential to phytoextract and phytostabilize metals from polluted soils. Using biochar and heavy metal accumulating plants constitutes an assisted phytostabilization strategy with great potential for HM polluted sites such as Cd and Pb.

Phytoaccumulation of zinc from contaminated soil using ornamental plants species Helianthus annuus L. and Tagetes erecta L

Intensive research on hyperaccumulator plant species provides an alternative method to cleanup heavy metal contaminated sites using these plants. Helianthus annuus and Tagetes erecta are suitable hyperaccumulator plant species for removing zinc (Zn) from contaminated soil because of their high phytoremediation effectiveness. The present study focused on to evaluate comparative efficacy of Zn accumulation using H. annuus and T. erecta. Plantlets were exposed to different Zn concentrations (10, 50, 100, 300, and 500 mg kg^-1) for 20, 40, and 60 days while changes in morphological, biochemical, and enzyme activity markers were evaluated. The concentration of Zn in various plant parts was determined using an atomic absorption spectrophotometer (AAS). After 60 days H. annuus showed greatest accumulation of Zn in the root and shoot (216.7 and 109.5 mg kg^-1), whereas the Zn accumulation T. erecta (209.5 and 97.84 mg kg^-1) was found comparatively less in the root and shoot. The result showed increased polyphenol and proline concentrations with increasing Zn concentrations which were maximal in H. annuus 6.642 mg g^-1 and 25.474 µmol g^-1, respectively. At 60 days, APX (4.145 mM mg^-1), CAT (2.558 mM mg^-1), and GR (52.23 mM mg^-1) antioxidant enzymatic activities were observed with higher concentrations. Analysis of ultrastructure confirmed Zn transport and localization in root and shoot tissues examined through FESEM-EDX, Fluorescence microscopy, and optical microscopy. The present research findings concluded with the high amount of removal of Zn from contaminated soil using H. annuus and T. erecta for ecofriendly approach to soil cleanup followed by sustainable agriculture.

Effects of Heavy Metal Stress on Physiology, Hydraulics, and Anatomy of Three Desert Plants in the Jinchang Mining Area, China

The physiological mechanisms and phytoremediation effects of three kinds of native quinoa in a desert mining area were studied. We used two different types of local soils (native soil and tailing soil) to analyze the changes in the heavy metal content, leaf physiology, photosynthetic parameters, stem hydraulics, and anatomical characteristics of potted quinoa. The results show that the chlorophyll content, photosynthetic rate, stomatal conductance, and transpiration rate of Kochia scoparia were decreased, but intercellular CO₂ concentration (Ci) was increased under heavy metal stress, and the net photosynthetic rate (Pn) was decreased due to non-stomatal limitation. The gas exchange of Chenopodium glaucum and Atriplex centralasiatica showed a decrease in Pn, stomatal conductance (Gs), and transpiration rate (E) due to stomatal limitation. The three species showed a similar change in heavy metal content; they all showed elevated hydraulic parameters, decreased vessel density, and significantly thickened vessel walls under heavy metal stress. Physiological indicators such as proline content and activity of superoxide dismutase (SOD) and peroxidase (POD) increased, but the content of malondialdehyde (MDA) and glutathione (GSH), as well as catalase (CAT) activity, decreased in these three plants. Therefore, it can be concluded that these three species of quinoa, possibly the most dominant 30 desert plants in the region, showed a good adaptability and accumulation capacity under the pressure of heavy metal stress, and these plants can be good candidates for tailings remediation in the Jinchang desert mining area.

Phytotoxicity level and accumulation ability of pot marigold (Calendula officinalis L.) to zinc

The study aims to reveal the effects of different Zn levels on pot marigold. We determined some germination and young seedling properties in the first experiment, and morphological, stomatal, and physiological parameters besides uptake profiles of both Zn and other plant nutrients in the second one. We supplied the water requirement of the seeds with Zn solutions (0, 250, 500, 750, and 1,000 mg l-1) in the first experiment, and We added the same zinc doses as mg kg-1 to the soil of the pots where the plants would grow in the second one. As a result, the inhibitory effects were more prominent in the early seedling stage (especially at 1,000 mg l-1 Zn) than in the germination one. We determined plant growth retardation, decreases in leaf water contents, and increases in membrane damages with higher Zn (≥500 mg kg-1) in the experiment conducted by potting soil. We detected decreases in chlorophyll parameters parallel with the increases in Zn. The alterations in plant zinc contents revealed the accumulation capacity of pot marigold in potting conditions. That TF value >1 in Zn treatments up to 500 mg kg-1 points to the efficiency limit of pot marigold as a Zn-accumulator plant.

A Hormetic Spatiotemporal Photosystem II Response Mechanism of Salvia to Excess Zinc Exposure

Exposure of Salvia sclarea plants to excess Zn for 8 days resulted in increased Ca, Fe, Mn, and Zn concentrations, but decreased Mg, in the aboveground tissues. The significant increase in the aboveground tissues of Mn, which is vital in the oxygen-evolving complex (OEC) of photosystem II (PSII), contributed to the higher efficiency of the OEC, and together with the increased Fe, which has a fundamental role as a component of the enzymes involved in the electron transport process, resulted in an increased electron transport rate (ETR). The decreased Mg content in the aboveground tissues contributed to decreased chlorophyll content that reduced excess absorption of sunlight and operated to improve PSII photochemistry (Φ_PSII), decreasing excess energy at PSII and lowering the degree of photoinhibition, as judged from the increased maximum efficiency of PSII photochemistry (Fv/Fm). The molecular mechanism by which Zn-treated leaves displayed an improved PSII photochemistry was the increased fraction of open PSII reaction centers (qp) and, mainly, the increased efficiency of the reaction centers (Fv′/Fm′) that enhanced ETR. Elemental bioimaging of Zn and Ca by laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) revealed their co-localization in the mid-leaf veins. The high Zn concentration was located in the mid-leaf-vein area, while mesophyll cells accumulated small amounts of Zn, thus resembling a spatiotemporal heterogenous response and suggesting an adaptive strategy. These findings contribute to our understanding of how exposure to excess Zn triggered a hormetic response of PSII photochemistry. Exposure of aromatic and medicinal plants to excess Zn in hydroponics can be regarded as an economical approach to ameliorate the deficiency of Fe and Zn, which are essential micronutrients for human health.

Zinc toxicity response in Ceratoides arborescens and identification of CaMTP, a novel zinc transporter

Zinc (Zn) is an essential micronutrient for several physiological and biochemical processes. Changes in soil Zn levels can negatively affect plant physiology. Although the mechanism of Zn nutrition has been studied extensively in crops and model plants, there has been little research on steppe plants, particularly live in alkaline soils of arid and semiarid regions. Ceratoides arborescens is used in arid and semiarid regions as forage and ecological restoration germplasm, which is studied can enrich the mechanism of Zn nutrition. The plants were exposed to three different Zn treatments, Zn-deficient (-Zn 0 mM L^-1), Zn-normal (Control, 0.015 mM L^-1), and Zn-excess (+Zn, 0.15 mM L^-1), for 3 weeks. Individual biomass, ion concentrations, photosynthetic system, and antioxidant characteristics were measured. High Zn supply significantly decreased plant biomass and induced chlorosis and growth defects and increased Zn concentration but decreased Fe and Ca concentrations, unlike in controls (p < 0.05). High Zn supply also reduced plant chlorophyll content, which consequently decreased the photosynthesis rate. Increased concentrations of malondialdehyde and soluble sugar and activities of peroxidase and superoxide dismutase could resist the high-level Zn stress. In contrast, low Zn supply did not affect plant growth performance. We also identified a novel protein through RNA transcriptome analysis, named CaMTP, that complemented the sensitivity of a yeast mutant to excessive Zn, which was found to be localized to the endoplasmic reticulum through transient gene expression in Nicotiana benthamiana. The gene CaMTP identified to be highly sensitive to Zn stress is a potential candidate for overcoming mineral stress in dicot crop plants.

A new mushroom hyperaccumulator: Cadmium and arsenic in the ectomycorrhizal basidiomycete Thelephora penicillata

Fruit-bodies of six Thelephora species (Fungi, Basidiomycota, Thelephoraceae) were analyzed for their trace element concentrations. In Thelephora penicillata, extremely high concentrations of Cd and As were found, followed by highly elevated concentrations of Cu and Zn. The highest accumulation ability was found for Cd with a mean concentration of 1.17 ± 0.37 g kg^-1 (dry mass) in fruit-bodies collected from 20 unpolluted sites; the mean As concentration was 0.878 ± 0.242 g kg^-1. Furthermore, striking accumulation of Se (923 ± 28 mg kg^-1) was found in one sample of T. vialis and elevated concentrations of S were detected in T. palmata (19.6 ± 5.9 g kg^-1). The analyzed Thelephora species were sequenced and, based on the Maximum Likelihood phylogenetic analysis (ITS rDNA) of the genus, possible other Thelephora (hyper)accumulators were predicted on the basis of their phylogenetic relationship with the discovered (hyper)accumulators. The striking ability of T. penicillata to accumulate simultaneously Cd, As, Cu, and Zn has no parallel in the Fungal Kingdom and raises the question of a biological importance of metal(loid) hyperaccumulation in mushrooms.

Identification of heavy metals tolerant Brevundimonas sp. from rhizospheric zone of Saccharum munja L. and their efficacy in in-situ phytoremediation

Heavy metals phytoremediation from pulp and paper industry (PPI) sludge was conducted by employing root-associated Brevundimonas sp (PS-4 MN238722.1) in rhizospheric zone of Saccharum munja L. for its detoxification. The study was aimed to investigate the efficiency of Saccharum munja L. for the removal of heavy metals along with physico-chemical parameters through bacterial interactions. Physico-chemical examination of PPI sludge showed biochemical oxygen demand (8357 ± 94 mg kg^-1), electrical conductivity (2264 ± 49 μmhoscm^-1), total phenol (521 ± 24 mg kg^-1), total dissolve solid (1547 ± 23 mg kg^-1), total nitrogen (264 ± 2.13 mg kg^-1), pH (8.2 ± 0.11), chemical oxygen demand (34756 ± 214 mg kg^-1), color (2434 ± 45 Co-Pt), total suspended solid (76 ± 0.67 mg kg^-1), sulphate (2462 ± 13 mg kg^-1), chlorolignin (597 ± 13.01 mg kg^-1), K⁺ (21.04 ± 0.26 mg kg^-1), total solid (1740 ± 54 mg kg^-1), phosphorous, Cl^-, and Na⁺. Heavy metals, such as Fe followed by Zn, Mn, Cd, Cu, Ni, Pb, As, Cr and Hg were above the permissible limit. Root and shoot of Saccharum munja L. revealed highest concentrations of Cd followed by Mn, Ni, Fe, Zn, Cu, As, Cr, Hg, and Pb. Tested metals (Fe, Mn, Pb, Cd, Cr, Cu, Zn, Ni, As, and Hg) bioaccumulation and translocation factors were also revealed to be < 1 and >1, respectively, demonstrating that these plants have considerable absorption and translocation abilities. Plant growth-promoting activity, such as ligninolytic enzymes, hydrolytic enzymes, indole acetic acid, and siderophore production activity of Brevundimonas sp. (PS-4 MN238722.1) were also noted to be higher. These findings support the use of Brevundimonas sp (PS-4 MN238722.1) in combination with Saccharum munja L. plant as interdisciplinary management of industrial sludge at polluted areas for the prevention of soils near the industrial site.

An Assessment of the Metal Removal Capability of Endemic Chilean Species

In Chile, there are several abandoned mine tailing impoundments near population centers that need to be remediated. In this study, the ability of Oxalis gigantea, Cistanthe grandiflora, and Puya berteroniana to remove Zn, Ni, and Cr from mine tailings was evaluated. The plants’ removal efficiency, bioconcentration, and translocation factors regarding these metals were determined to assess the ability of certain endemic species from Northern and Central Chile to extract or stabilize metals. After a period of seven months, the chemical analysis of plants and tailings, together with the statistical treatment of data, indicated the inability of all the species to translocate Ni, Cr, or Zn with a translocation factor lower than one. The results showed the stabilizing character of Oxalis gigantea, Puya berteroniana, and Cistanthe grandiflora for Zn, with a bioconcentration factor close to 1.2 in all cases, and the same ability of the latter two species for Cr, with a bioconcentration factor of 1.5 in the case of Cistanthe grandiflora and 1.7 for Puya berteroniana. Finally, a removal efficiency of 9.3% was obtained with Cistanthe grandiflora for Cr and 15% for Ni; values lower than 6.4% were obtained for Zn in all cases. Improvements in the process should be sought to enhance the performance of these species for the accumulation of the target metals.

AtTIP2;2 facilitates resistance to zinc toxicity via promoting zinc immobilization in the root and limiting root-to-shoot zinc translocation in Arabidopsis thaliana

Zinc (Zn) is an essential micronutrient for plants. However, excess Zn is toxic to non-accumulating plants like Arabidopsis thaliana. To cope with Zn toxicity, non-accumulating plants need to keep excess Zn in the less sensitive root tissues and restrict its translocation to the vulnerable shoot tissues, a process referred to as Zn immobilization in the root. However, the mechanism underlying Zn immobilization is not fully understood. In Arabidopsis, sequestration of excess Zn to the vacuole of root cells is crucial for Zn immobilization, facilitated by distinct tonoplast-localized transporters. As some members of the aquaporin superfamily have been implicated in transporting metal ions besides polar but non-charged small molecules, we tested whether Arabidopsis thaliana tonoplast intrinsic proteins (AtTIPs) could be involved in Zn immobilization and resistance. We found that AtTIP2;2 is involved in retaining excess Zn in the root, limiting its translocation to the shoot, and facilitating its accumulation in the leaf trichome. Furthermore, when expressed in yeast, the tonoplast-localized AtTIP2;2 renders glutathione (GSH)-dependent Zn resistance to yeast cells, suggesting that AtTIP2;2 facilitates the across-tonoplast transport of GSH-Zn complexes. Our findings provide new insights into aquaporins' roles in heavy metal resistance and detoxification in plants.

Effects of Cu and Zn contamination on chicken manure-based bioponics: Nitrogen recovery, bioaccumulation, microbial community, and health risk assessment

In bioponics, although chicken manure is an efficient substrate for vegetable production and nitrogen recovery, it is often contaminated with high Cu and Zn levels, which could potentially cause bioaccumulation in plants and pose health risks. The objectives of this study were to assess nitrogen recovery in lettuce- and pak choi-based bioponics with Cu (50-150 mg/kg) and Zn (200-600 mg/kg) supplementation, as well as their bioaccumulation in plants, root microbial community, and health risk assessment. The supplementation of Cu and Zn did not affect nitrogen concentrations and plant growth (p > 0.05) but reduced nitrogen use efficiency. Pak choi showed higher Cu and Zn bioconcentration factors than lettuce. Bacterial genera Ruminiclostridium and WD2101_soil_group in lettuce roots and Mesorhizobium in pak choi roots from Cu and Zn supplemented conditions were significantly higher (p < 0.05) than controls, suggesting microbial biomarkers in plant roots from Cu and Zn exposure bioponics depended on plant type. Health risk assessment herein revealed that consumption of bioponic vegetables with Cu and Zn contamination does not pose long-term health risks (hazard index <1) to children or adults, according to the US EPA. This study suggested that vegetable produced from chicken manure-based bioponics has low health risk in terms of Cu and Zn bioaccumulation and could be applied in commercial-scale system for nutrient recovery from organic waste to vegetable production; however, health risk from other heavy metals and xenobiotic compounds must be addressed.

Hormetic effects of zinc on growth and antioxidant defense system of wheat plants

Although hormesis induced by heavy metals is a well-known phenomenon, the involved biological mechanisms are not fully understood. Zinc (Zn) is an essential micronutrient for wheat, an important crop contributing to food security as a main staple food; however, excessive Zn is detrimental to the growth of wheat. The aim of this study was to evaluate morphological and physiological responses of two wheat varieties exposed to a broad range of Zn concentrations (0-1000 μM) for 14 days. Hormesis was induced by Zn in both wheat varieties. Treatment with 10-100 μM Zn promoted biomass accumulation by enhancing the photosynthetic ability, the chlorophyll content and the activities of antioxidant enzymes. Increased root/shoot ratio suggested that shoot growth was severely inhibited when Zn concentration exceeded 300 μM by reducing photosynthetic ability and the content of photosynthetic pigments. Excessive Zn accumulation (Zn treatment of 300-1000 μM) in leaf and root induced membrane injuries through lipid peroxidation as malondialdehyde (MDA) content increased with increasing Zn concentration. The results show that MDA content was higher than other treatments by 16.1-151.1% and 15.0-88.3% (XN979) and 36.8-235.7% and 20.6-83.8% (BN207) in the leaves and roots under 1000 μM Zn treatment. To defend against Zn toxicity, ascorbate (AsA), glutathione (GSH), non-protein thiols (NPT) and phytochelatin (PC) content of both wheat varieties (except leaf GSH content of BN207) was increased, while, the activities of superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, and the content of soluble protein decreased by 300-1000 μM Zn. The results showed that AsA-GSH cycle and NPT and PC content of wheat seedlings play important roles in defending against Zn toxicity. This study contributes new insights into the physiological mechanisms underlying the hormetic response of wheat to Zn, which could be beneficial for optimizing plant health in changing environments and improving risk assessments.

Impact of nanoparticles and their ionic counterparts derived from heavy metals on the physiology of food crops

Heavy metals and their engineered nanoparticle (NP) counterparts are emerging contaminants in the environment that have captured the attention of researchers worldwide. Although copper, iron, zinc and manganese are essential micronutrients for food crops, higher concentrations provoke several physiological and biochemical alterations that in extreme cases can lead to plant death. The effects of heavy metals on plants have been studied but the influence of nanoparticles (NPs) derived from these heavy metals, and their comparative effect is less known. In this critical review, we have found similar impacts for copper and manganese ionic and NP counterparts; in contrast, iron and zinc NPs seem less toxic for food crops. Although these nutrients are metals that can be dissociated in water, few authors have conducted joint ionic state and NP assays to evaluate their comparative effect. More efforts are thus required to fully understand the impact of NPs and their ion counterparts at the physiological, metabolic and molecular dimensions in crop plants.

Phytoremediation technology and food security impacts of heavy metal contaminated soils: A review of literature

Heavy metal accumulation in soil and water is one of major problems caused by inorganic contaminants. Their presence in agricultural soils in high quantities have impacted the food security significantly and, by extension, the human health. Amongst various physico-chemical methods available for remediation of heavy-metals-polluted-sites, phytoremediation approaches have been found to be safe and environment friendly. This review gathered scattered information on heavy metal phytoremediation studies published in both review and research articles. It described the impact of heavy metals on food security and comprehensively discussed the application of different phytoremediation approaches for treatment of heavy metal-polluted soils, the basic principles underlining them, their strengths and weaknesses. Our findings indicated that, while hundreds of hyper-accumulator plants are being reported yearly, only few describe limitations inherent in them, such as low growth rate, low biomass production, and low metal tolerance. Hence, this review also gave a detailed overview of research gaps in phytotechnology and advocates consideration of the 'omics' studies; genomics, proteomics, metabolomics and likes in selecting and enhancing potential plants for phytoremediation. For a sustainable large-scale phytoremediation application, we established a multi-technology repair strategy via the combination of different methods like application of biological composts, plant-growth promoting microorganisms, and phytohormones for stimulation of the plant-growth during phytoremediation. We also gave comprehensive insights to proper disposal of plants used for phytoremediation, this subject is often not well considered/planned while deciding the application of plants for removal of heavy metals from polluted environments.

Zinc in plants: Integrating homeostasis and biofortification

Zinc plays many essential roles in life. As a strong Lewis acid that lacks redox activity under environmental and cellular conditions, the Zn²⁺ cation is central in determining protein structure and catalytic function of nearly 10% of most eukaryotic proteomes. While specific functions of zinc have been elucidated at a molecular level in a number of plant proteins, wider issues abound with respect to the acquisition and distribution of zinc by plants. An important challenge is to understand how plants balance between Zn supply in soil and their own nutritional requirement for zinc, particularly where edaphic factors lead to a lack of bioavailable zinc or, conversely, an excess of zinc that bears a major risk of phytotoxicity. Plants are the ultimate source of zinc in the human diet, and human Zn deficiency accounts for over 400 000 deaths annually. Here, we review the current understanding of zinc homeostasis in plants from the molecular and physiological perspectives. We provide an overview of approaches pursued so far in Zn biofortification of crops. Finally, we outline a "push-pull" model of zinc nutrition in plants as a simplifying concept. In summary, this review discusses avenues that can potentially deliver wider benefits for both plant and human Zn nutrition.

The Combined Effect of ZnO and CeO2 Nanoparticles on Pisum sativum L.: A Photosynthesis and Nutrients Uptake Study

Cerium oxide nanoparticles (CeO2 NPs) and zinc oxide nanoparticles (ZnO NPs) are emerging pollutants that are likely to occur in the contemporary environment. So far, their combined effects on terrestrial plants have not been thoroughly investigated. Obviously, this subject is a challenge for modern ecotoxicology. In this study, Pisum sativum L. plants were exposed to either CeO2 NPs or ZnO NPs alone, or mixtures of these nano-oxides (at two concentrations: 100 and 200 mg/L). The plants were cultivated in hydroponic system for twelve days. The combined effect of NPs was proved by 1D ANOVA augmented by Tukey's post hoc test at p = 0.95. It affected all major plant growth and photosynthesis parameters. Additionally, HR-CS AAS and ICP-OES were used to determine concentrations of Cu, Mn, Fe, Mg, Ca, K, Zn, and Ce in roots and shoots. Treatment of the pea plants with the NPs, either alone or in combination affected the homeostasis of these metals in the plants. CeO2 NPs stimulated the photosynthesis rate, while ZnO NPs prompted stomatal and biochemical limitations. In the mixed ZnO and CeO2 treatments, the latter effects were decreased by CeO2 NPs. These results indicate that free radicals scavenging properties of CeO2 NPs mitigate the toxicity symptoms induced in the plants by ZnO NPs.

The multifactorial assessment of the Zn impact on high and low temperature stress towards wheat seedling growth under diverse moisture conditions (optimal and wet) in three soils

Anthropogenic activities leading to chemical contamination of soil and global climate change may increase the level of stress for plants. Recent decades studies (mainly two-factors) have reported that the ecotoxicity of soil contaminants could be modified by climate factors. To date, little is known about: the combined climate-chemical stress on plants; the interaction of chemicals with high soil moisture conditions; the impact of soil properties on the combined climate-chemical stress and questions regarding the response of organisms to combined effect of all key factors influencing the ecotoxicity of chemicals under field conditions remain unanswered. Our study sought to fill the knowledge gap on the multifactorial interaction of four main factors encounter in polluted areas (soil chemical contamination: heavy metal (Zn); temperature: 10, 23, 35 °C, moisture: 55, 80%WHC; soil properties). The assessment of combined effect of multiple stressors based on the multiple ANCOVA model (n = 108; adjusted R² = 0.68) and calculated indicators showed: 1) all studied factors significantly interacted and influenced the phytotoxic effect of Zn; 2) Zn modified the plant response to temperature stress depending on moisture conditions and soil properties. This study improves methods for assessing the hazardous effects of soil chemical contamination in the real environment.

Competition for light induces metal accumulation in a metal hyperaccumulating plant

Plants can respond to competition with a myriad of physiological or morphological changes. Competition has also been shown to affect the foraging decisions of plants belowground. However, a completely unexplored idea is that competition might also affect plants' foraging for specific elements required to inhibit the growth of their competitors. In this study, we examined the effect of simulated competition on root foraging and accumulation of heavy metals in the metal hyperaccumulating perennial plant Arabidopsis halleri, whose metal accumulation has been shown to provide allelopathic ability. A. halleri plants originating from both metalliferous and non-metalliferous soils were grown in a "split-root" setup with one root in a high-metal pot and the other in a low-metal one. The plants were then assigned to either simulated light competition or no-competition (control) treatments, using vertical green or clear plastic filters, respectively. While simulated light competition did not induce greater root allocation into the high-metal pots, it did result in enhanced metal accumulation by A. halleri, particularly in the less metal-tolerant plants, originating from non-metalliferous soils. Interestingly, this accumulation response was particularly enhanced for zinc rather than cadmium. These results provide support to the idea that the accumulation of metals by hyperaccumulating plants can be facultative and change according to their demand following competition.

Nutritional and Functional Evaluation of Inula crithmoides and Mesembryanthemum nodiflorum Grown in Different Salinities for Human Consumption

The nutritional composition and productivity of halophytes is strongly related to the biotic/abiotic stress to which these extremophile salt tolerant plants are subjected during their cultivation cycle. In this study, two commercial halophyte species (Inula crithmoides and Mesembryanthemum nodiflorum) were cultivated at six levels of salinity using a soilless cultivation system. In this way, it was possible to understand the response mechanisms of these halophytes to salt stress. The relative productivity decreased from the salinities of 110 and 200 mmol L⁻¹ upwards for I. crithmoides and M. nodiflorum, respectively. Nonetheless, the nutritional profile for human consumption remained balanced. In general, I. crithmoides vitamin (B1 and B6) contents were significantly higher than those of M. nodiflorum. For both species, β-carotene and lutein were induced by salinity, possibly as a response to oxidative stress. Phenolic compounds were more abundant in plants cultivated at lower salinities, while the antioxidant activity increased as a response to salt stress. Sensory characteristics were evaluated by a panel of culinary chefs showing a preference for plants grown at the salt concentration of 350 mmol L⁻¹. In summary, salinity stress was effective in boosting important nutritional components in these species, and the soilless system promotes the sustainable and safe production of halophyte plants for human consumption.

Exogenous application of ZnO nanoparticles and ZnSO4 distinctly influence the metabolic response in Phaseolus vulgaris L

Nanomaterials-mediated contamination (including the highly reactive metal oxides ZnO nanoparticles) is becoming one of the most concerning issues worldwide. In this study, the toxic effects of two chemical species of Zn (ZnO nanoparticles and bulk ZnSO₄) were investigated in bean plants, following either foliar or soil application, at concentrations from 250 to 2000 mg L^-1 using biochemical assays, proteomics and metabolomics. The accumulation of Zn in plant tissues depended on the application type, zinc chemical form and concentration, in turn triggering distinctive morphological, physiological, and redox responses. Bean plants were more sensitive to the foliar than to the soil application, and high concentrations of ZnO NP and bulk ZnSO₄ determined the highest plant growth inhibition and stress symptoms. However, low dosages of ZnSO₄ induced a slight plant growth promotion and better physiological and antioxidative response. Low concentration of Zn leaded to increased activity of stress-related proteins and secondary metabolites with antioxidant capacity, while increasing concentration reached the exhausted phase of the plant stress response, reducing the antioxidant defense system. Such high concentrations increased lipids peroxidation, protein degradation and membranes integrity. Oxidative damage occurred at high concentrations of both chemical species of Zn. Foliar spraying impaired photosynthetic efficiency, while soil applications (especially ZnSO₄) elicited antioxidant metabolites and proteins, and impaired chloroplast-related proteins involved in the electron transport chain and ATP production. Taken together, the results highlighted distinctive and nanoparticles-related toxic effects of ZnO in bean, compared to ionic forms of Zn.

The Different Faces of Arabidopsis arenosa-A Plant Species for a Special Purpose

The following review article collects information on the plant species Arabidopsis arenosa. Thus far, A. arenosa has been known as a model species for autotetraploidy studies because, apart from diploid individuals, there are also tetraploid populations, which is a unique feature of this Arabidopsis species. In addition, A arenosa has often been reported in heavy metal-contaminated sites, where it occurs together with a closely related species A. halleri, a model plant hyperaccumulator of Cd and Zn. Recent studies have shown that several populations of A. arenosa also exhibit Cd and Zn hyperaccumulation. However, it is assumed that the mechanism of hyperaccumulation differs between these two Arabidopsis species. Nevertheless, this phenomenon is still not fully understood, and thorough research is needed. In this paper, we summarize the current state of knowledge regarding research on A. arenosa.

Endophytic Nanotechnology: An Approach to Study Scope and Potential Applications

Nanotechnology has become a very advanced and popular form of technology with huge potentials. Nanotechnology has been very well explored in the fields of electronics, automobiles, construction, medicine, and cosmetics, but the exploration of nanotecnology's use in agriculture is still limited. Due to climate change, each year around 40% of crops face abiotic and biotic stress; with the global demand for food increasing, nanotechnology is seen as the best method to mitigate challenges in disease management in crops by reducing the use of chemical inputs such as herbicides, pesticides, and fungicides. The use of these toxic chemicals is potentially harmful to humans and the environment. Therefore, using NPs as fungicides/ bactericides or as nanofertilizers, due to their small size and high surface area with high reactivity, reduces the problems in plant disease management. There are several methods that have been used to synthesize NPs, such as physical and chemical methods. Specially, we need ecofriendly and nontoxic methods for the synthesis of NPs. Some biological organisms like plants, algae, yeast, bacteria, actinomycetes, and fungi have emerged as superlative candidates for the biological synthesis of NPs (also considered as green synthesis). Among these biological methods, endophytic microorganisms have been widely used to synthesize NPs with low metallic ions, which opens a new possibility on the edge of biological nanotechnology. In this review, we will have discussed the different methods of synthesis of NPs, such as top-down, bottom-up, and green synthesis (specially including endophytic microorganisms) methods, their mechanisms, different forms of NPs, such as magnesium oxide nanoparticles (MgO-NPs), copper nanoparticles (Cu-NPs), chitosan nanoparticles (CS-NPs), β-d-glucan nanoparticles (GNPs), and engineered nanoparticles (quantum dots, metalloids, nonmetals, carbon nanomaterials, dendrimers, and liposomes), and their molecular approaches in various aspects. At the molecular level, nanoparticles, such as mesoporous silica nanoparticles (MSN) and RNA-interference molecules, can also be used as molecular tools to carry genetic material during genetic engineering of plants. In plant disease management, NPs can be used as biosensors to diagnose the disease.