Plant-lead interactions: Transport, toxicity, tolerance, and detoxification mechanisms

Lead toxicity in plants: mechanistic insights into toxicity, physiological responses of plants and mitigation strategies

Soil toxicity is a major environmental issue that leads to numerous harmful effects on plants and human beings. Every year a huge amount of Pb is dumped into the environment either from natural sources or anthropogenically. Being a heavy metal it is highly toxic and non-biodegradable but remains in the environment for a long time. It is considered a neurotoxic and exerts harmful effects on living beings. In the present review article, investigators have emphasized the side effects of Pb on the plants. Further, the authors have focused on the various sources of Pb in the environment. Investigators have emphasized the various responses including molecular, biochemical, and morphological of plants to the toxic levels of Pb. Further emphasis was given to the effect of elevated levels of Pb on the microbial population in the rhizospheres. Further, emphasized the various remediation strategies for the Pb removal from the soil and water sources.

Sulfur availability and nodulation modify the response of Robinia pseudoacacia L. to lead (Pb) exposure

Both sulfur (S) supply and legume-rhizobium symbiosis can significantly contribute to enhancing the efficiency of phytoremediation of heavy metals (HMs). However, the regulatory mechanism determining the performance of legumes at lead (Pb) exposure have not been elucidated. Here, we cultivated black locust (Robinia pseudoacacia L.), a leguminous woody pioneer species at three S supply levels (i.e., deficient, moderate, and high S) with rhizobia inoculation and investigated the interaction of these treatments upon Pb exposure. Our results revealed that the root system of Robinia has a strong Pb accumulation and anti-oxidative capacity that protect the leaves from Pb toxicity. Compared with moderate S supply, high S supply significantly increased Pb accumulation in roots by promoting the synthesis of reduced S compounds (i.e., thiols, phytochelatin), and also strengthened the antioxidant system in leaves. Weakened defense at deficient S supply was indicated by enhanced oxidative damage. Rhizobia inoculation alleviated the oxidative damage of its Robinia host by immobilizing Pb to reduce its absorption by root cells. Together with enhanced Pb chelation in leaves, these mechanisms strengthen Pb detoxification in the Robinia-rhizobia symbiosis. Our results indicate that appropriate S supply can improve the defense of legume-rhizobia symbiosis against HM toxicity.

Remediation of heavy metals polluted soil environment: A critical review on biological approaches

Heavy metals (HMs) pollution is a globally emerging concern. It is difficult to cost-effectively combat such HMs polluted soil environments. The efficient remediation of HMs polluted soil is crucial to protect human health and ecological security that could be carried out by several methods. Amidst, biological remediation is the most affordable and ecological. This review focused on the principles, mechanisms, performances, and influential factors in bioremediation of HMs polluted soil. In microbial remediation, microbes can alter metallic compounds in soils. They transform these compounds into their metabolism through biosorption and bioprecipitation. The secreted microbial enzymes act as transformers and assist in HMs immobilization. The synergistic microbial effect can further improve HMs removal. In bioleaching, the microbial activity can simultaneously produce H2SO4 or organic acids and leach HMs. The production of acids and the metabolism of bacteria and fungi transform metallic compounds to soluble and extractable form. The key bioleaching mechanisms are acidolysis, complexolysis, redoxolysis and bioaccumulation. In phytoremediation, hyperaccumulator plants and their rhizospheric microbes absorb HMs by roots through absorption, cation exchange, filtration, and chemical changes. Then they exert different detoxification mechanisms. The detoxified HMs are then transferred and accumulated in their harvestable tissues. Plant growth-promoting bacteria can promote phytoremediation efficiency; however, use of chelants have adverse effects. There are some other biological methods for the remediation of HMs polluted soil environment that are not extensively practiced. Finally, the findings of this review will assist the practitioners and researchers to select the appropriate bioremediation approach for a specific soil environment.

Significant lead isotope 'fractionation' in maize records plant lead uptake, transfer, and detoxification mechanisms

Lead isotope analysis is the main method to trace the sources and cycling of Pb in the biosphere system. The linchpin of such application hinges on the assumption that there is negligible or no biologically mediated isotopic fractionation of Pb occurs in the environment. However, recent measurements by high-precision multi-collector mass spectrometry revealed that biological isotope fractionation of heavy mass elements is a prevalent phenomenon. This study shows that compared with the Pb sources, the maize plant (Zea mays L.) organs exhibit a wider range of Pb isotope compositions and a depletion of radioactive Pb isotopes (206Pb, 207Pb, and 208Pb). Moreover, three independent studies consistently indicate that the 206Pb/207Pb ratio of maize organs varies as root/leaf > stem/grain, reflecting a continuous loss of light Pb isotopes during transportation. The conventional wisdom fails to account for these phenomena, suggesting that maize may undergo Pb isotope fractionation during the absorption and transportation of Pb. However, compared with other non-traditional metal isotopes, Pb isotope exhibits a more significant fractionation magnitude. We tentatively attribute this fractionation to the Pb tolerance mechanism of maize and its selective absorption of various forms of Pb, which requires further research to validate. Findings from this study mandate caution in future Pb source tracing in plants using Pb isotope methods and open up applications in using Pb isotopic fractionation to track Pb uptake and transfer pathways and decipher the associated detoxification mechanisms in plants.

Natural colonizers effectively restore heavy metal polluted wasteland

In India, ∼30% of total land is degraded due to pollution, salinization, and nutrient loss. Change in soil-quality at urban waste-dumping site prior and after cow-dung amendment was compared with control agriculture soil. The soil at waste-dumping site had elevated pH, EC, temperature and lowered OC and NPK concentrations when compared to control. Polymetallic pollution of Cr, Cd, Pb, and Ni beyond permissible limits was obtained. Cow-dung amendment restored soil physicochemical properties at the waste-dumping site, with increasing soil moisture, CEC and OC; however, a slight change in soil bulk-density and heavy-metal concentration post-amendment was noted. The seven natural colonizers present at the waste-dumping site accumulated more metals in roots than shoots. Datura innoxia had maximum bioaccumulation of Cr, Calotropis procera of Cd and Ni and Parthenium hysterophorus of Pb in roots. All these plants had Bioacccumulation factor (BAfroot )>1 and translocation factor (Tf) <1 for Cd and serve as its phytostabilizer except Calotropis procera which had BAfroot >1 and Tf >1 and is identified as a phytoextractor for Cd. Cow-dung amendment alone appeared to be insufficient and additionally the revegetation of natural colonizers is recommended for effective reduction in heavy metal load and improving overall soil health at wasteland. Such eco-restoration may also minimize risks to biodiversity in India.

Targeting JAK2/STAT3, NLRP3/Caspase-1, and PK2/PKR2 Pathways with Arbutin Ameliorates Lead Acetate-Induced Testicular Injury in Rats

The reproductive system of males is adversely impacted by lead (Pb), a toxic heavy metal. The present study examined arbutin, a promising hydroquinone glycoside, for its potential ameliorative impact against Pb-induced testicular impairment in rats. The testicular injury was induced by the intraperitoneal administration of Pb acetate (20 mg/kg/day) for 10 consecutive days. Thirty-six rats were divided into six experimental groups (n = 6 per group): control, control treated with oral arbutin (250 mg/kg), control treated with intraperitoneal arbutin (75 mg/kg), untreated Pb, Pb treated with oral arbutin, and Pb treated with intraperitoneal arbutin. The treatments were administered daily for 10 days. Arbutin was administered by the oral and intraperitoneal routes to compare the efficacy of both routes in mitigating Pb acetate-induced testicular dysfunction. The current data revealed that both oral and intraperitoneal administration of arbutin significantly enhanced serum testosterone and sperm count/motility, indicating the amelioration of testicular dysfunction. In tandem, both routes lowered testicular histopathological aberrations and Johnsen's damage scores. These favorable outcomes were driven by dampening testicular oxidative stress, evidenced by lowered lipid peroxidation and increased glutathione and catalase antioxidants. Moreover, arbutin lowered testicular p-JAK2 and p-STAT3 levels, confirming the inhibition of the JAK2/STAT3 pro-inflammatory pathway. In tandem, arbutin suppressed the testicular NLRP3/caspase-1/NF-B axis and augmented the cytoprotective PK2/PKR2 pathway. Notably, intraperitoneal arbutin at a lower dose prompted a more pronounced mitigation of Pb-induced testicular dysfunction compared to oral administration. In conclusion, arbutin ameliorates Pb-evoked testicular damage by stimulating testicular antioxidants and the PK2/PKR2 pathway and inhibiting the JAK2/STAT3 and NLRP3/caspase-1 pro-inflammatory pathways. Hence, arbutin may be used as an adjunct agent for mitigating Pb-induced testicular impairment.

Unravelling the halophyte Suaeda maritima as an efficient candidate for phytostabilization of cadmium and lead: Implications from physiological, ionomic, and metabolomic responses

Cadmium (Cd) and lead (Pb) are among the most toxic heavy metals affecting human health and crop yield. Suaeda maritima (L.) Dumort is an obligate halophyte that is well adapted to saline soil. The inbuilt salinity tolerance mechanisms of halophytes help them to survive in heavy metal-contaminated rhizospheric soil. In the present study, growth and ionomic responses, reactive oxygen species (ROS) accumulation, modulations of phytochelatins, antioxidative defense, and metabolomic responses were studied in S. maritima imposed to Cd and Pb stresses with an aim to elucidate Cd and Pb tolerance mechanisms and phytoremediation potential of this halophyte. Our results showed a reduction of biomass in S. maritima, which may serve as an energy conservation strategy for survival under heavy metal stress. The increased accumulation of ROS with concomitant higher expression of various antioxidative enzymes suggests the efficient scavenging of ROS. The metabolite profiling revealed significant up-regulation of sugars, sugar alcohols, amino acids, polyphenols, and organic acids under Cd and Pb stresses suggesting their possible role in osmotic balance, ionic homeostasis, ROS scavenging, and signal transduction for stress tolerance. In S. maritima, the translocation factors (Tf) are <1 in both Cd and Pb treatments, which indicates that this halophyte has high phytostabilization potential for Cd and Pb in roots and through restricted translocation of heavy metal ions to the aboveground part. The findings of this study offer comprehensive information on Cd and Pb tolerance mechanisms in S. maritima and suggest that this halophyte can detoxify the HMs through physiological, ionic, antioxidative, and metabolic regulations.

Cadmium Stress Signaling Pathways in Plants: Molecular Responses and Mechanisms

Heavy metal (HM) pollution, specifically cadmium (Cd) contamination, is a worldwide concern for its consequences for plant health and ecosystem stability. This review sheds light on the intricate mechanisms underlying Cd toxicity in plants and the various strategies employed by these organisms to mitigate its adverse effects. From molecular responses to physiological adaptations, plants have evolved sophisticated defense mechanisms to counteract Cd stress. We highlighted the role of phytochelatins (PCn) in plant detoxification, which chelate and sequester Cd ions to prevent their accumulation and minimize toxicity. Additionally, we explored the involvement of glutathione (GSH) in mitigating oxidative damage caused by Cd exposure and discussed the regulatory mechanisms governing GSH biosynthesis. We highlighted the role of transporter proteins, such as ATP-binding cassette transporters (ABCs) and heavy metal ATPases (HMAs), in mediating the uptake, sequestration, and detoxification of Cd in plants. Overall, this work offered valuable insights into the physiological, molecular, and biochemical mechanisms underlying plant responses to Cd stress, providing a basis for strategies to alleviate the unfavorable effects of HM pollution on plant health and ecosystem resilience.

Unveiling biochar potential to promote safe crop production in toxic metal(loid) contaminated soil: A meta-analysis

Biochar application emerges as a promising and sustainable solution for the remediation of soils contaminated with potentially toxic metal(loid)s (PTMs), yet its potential to reduce PTM accumulation in crops remains to be fully elucidated. In our study, a hierarchical meta-analysis based on 276 research articles was conducted to quantify the effects of biochar application on crop growth and PTM accumulation. Meanwhile, a machine learning approach was developed to identify the major contributing features. Our findings revealed that biochar application significantly enhanced crop growth, and reduced PTM concentrations in crop tissues, showing a decrease trend of grains (36.1%, 33.6 to 38.6%) > shoots (31.1%, 29.3 to 32.8%) > roots (27.5%, 25.7 to 29.2%). Furthermore, biochar modifications were found to amplify its remediation potential in PTM-contaminated soils. Biochar application was observed to provide favorable conditions for reducing PTM uptake by crops, primarily through decreasing available PTM concentrations and improving overall soil quality. Employing machine learning techniques, we identified biochar properties, such as surface area and C content as a key factor in decreasing PTM bioavailability in soil-crop systems. Furthermore, our study indicated that biochar application could reduce probabilistic health risks associated with of the presence of PTMs in crop grains, thereby contributing to human health protection. These findings highlighted the essential role of biochar in remediating PTM-contaminated lands and offered guidelines for enhancing safe crop production.

Effect of Secondary Paper Sludge on Physiological Traits of Lactuca sativa L. under Heavy-Metal Stress

To eliminate the negative effect of soil contamination with heavy metals on plant growth and crop yield, different methods and techniques are the subject of discussion and study. In this study, we aimed to evaluate the effect of secondary pulp and paper-mill sludge application to soil on the response of the main physiological processes such as the growth, photosynthesis, and respiration of lettuce (Lactuca sativa L.) plants to soil contamination with Pb. For the pot experiment, Pb was added to sandy loam soil at concentrations of 0, 50, and 250 mg Pb(NO3)2 per kg of the soil, and secondary sludge was added to a 0, 20, or 40% sludge solution during each plant watering. The Pb-mediated change in plant biomass allocation, decrease in the photosynthetic rate, increase in leaf respiration rate, and the degree of light inhibition of respiration were closely associated with increases in both root and shoot Pb content. For the Pb-free soil condition, secondary sludge application contributed to the allocation of plant biomass towards a greater accumulation in the shoots than in the roots. Although stomatal opening was not affected by either Pb or sludge, sludge application increased photosynthetic CO2 assimilation regardless of soil Pb content, which was associated with an increase in the electron-transport rate and carboxylase activity of Rubisco. Soil contamination with Pb significantly increased the ratio of respiration to photosynthesis, reflecting a shift in the carbon balance toward carbon losses in the leaves, but sludge application modified the coupling between the processes with a decrease in the proportion of respiratory carbon losses. The sludge-mediated recovery of the physiological processes of L. sativa reflected an increase in plant tolerance to soil contamination with heavy metals, the formation of which is associated with plant and soil adjustments initiated by secondary sludge application.

Removal of high lead concentration by hydroponic cultures of normal and transformed plants of Scirpus americanus Pers

Lead is a very toxic metal which affects human health. An alternative to remove it from contaminated water is the use of macrophytes, as Scirpus americanus Pers. This species is tolerant to salt and metals and has high biomass. The present research analyzed the capacity of hydroponic cultures of normal and transgenic plants (line T12) from S. americanus to remove high concentrations of lead. The antioxidant response of plants to metal exposure was also measured. The MINTEQ3.1 program was used to define the media composition in order to have the metal available to the plants. According to MINTEQ3.1 predictions, sulfate, phosphate, and molybdenum must be removed from the medium to avoid lead precipitation. Therefore, the plants were maintained in a modified Hoagland solution containing 100, 250, and 400 mg/L lead. The presence of metal did not affect the growth of roots and stems at all concentration tested. The normal and T12 plants accumulated 69,389 mg/kg and 45,297 mg/kg lead, respectively, and could be considered hyperaccumulators. Plant tolerance to lead mainly involved an increase in superoxide dismutase activity and glutathione accumulation. The bioconcentration factor indicated that S. americanus plants bioconcentrated between 192 and 300 times the metal; thus, S. americanus could be used for phytoremediation of water contaminated with a high concentration of lead.

Pb uptake, accumulation, and translocation in plants: Plant physiological, biochemical, and molecular response: A review

Lead (Pb) is a highly toxic contaminant that is ubiquitously present in the ecosystem and poses severe environmental issues, including hazards to soil-plant systems. This review focuses on the uptake, accumulation, and translocation of Pb metallic ions and their toxicological effects on plant morpho-physiological and biochemical attributes. We highlight that the uptake of Pb metal is controlled by cation exchange capacity, pH, size of soil particles, root nature, and other physio-chemical limitations. Pb toxicity obstructs seed germination, root/shoot length, plant growth, and final crop-yield. Pb disrupts the nutrient uptake through roots, alters plasma membrane permeability, and disturbs chloroplast ultrastructure that triggers changes in respiration as well as transpiration activities, creates the reactive oxygen species (ROS), and activates some enzymatic and non-enzymatic antioxidants. Pb also impairs photosynthesis, disrupts water balance and mineral nutrients, changes hormonal status, and alters membrane structure and permeability. This review provides consolidated information concentrating on the current studies associated with Pb-induced oxidative stress and toxic conditions in various plants, highlighting the roles of different antioxidants in plants mitigating Pb-stress. Additionally, we discussed detoxification and tolerance responses in plants by regulating different gene expressions, protein, and glutathione metabolisms to resist Pb-induced phytotoxicity. Overall, various approaches to tackle Pb toxicity have been addressed; the phytoremediation techniques and biochar amendments are economical and eco-friendly remedies for improving Pb-contaminated soils.

Application of thifluzamide to stem rot in peppers: Infection and control mechanisms of sclerotium rolfsii

In recent years, the fungal disease 'pepper stem rot', contracted from the soil-borne pathogen sclerotium rolfsii, has been increasing year by year, causing significant losses to the pepper (Capsicum annuum L.) industry. To investigate the infection mechanism of stem rot, the fungus S. rolfsii was used to infect the roots of pepper plants, and was found to affect root morphology and reduce root activity, which subsequently inhibited root growth and development. With fungal infestation, its secretions (oxalic acid, PG and PMG enzyme) were able to break normal tissues in the stem base and induced the burst of the active oxygen, which leads to injury aggravation. Morphological observations of the site of damage at the base of the stem using SEM revealed that the vascular bundles and stomata were completely blocked by hyphae, resulting in a blockade of material exchange in the plant. It was subsequently found that most of the stomata in the leaves were closed, which caused the leaves to lose their ability to photosynthesize, then turned yellow, wilt, shed, and the plant died. Commercialized fungicide thifluzamide with excellent in vitro (EC50 = 0.1 μg/mL) and in vivo curative (EC50 = 29.2 μg/mL) antifungal activity was selected to control the stem rot disease in peppers. The results demonstrated that it was able to suppress the secretion of associated pathogenic factors and reduce the outbursts of reactive oxygen species, thus reducing the damage caused by S. rolfsii at the base of the plant's stem and also enhancing the root activity of the infected plant, thereby promoting root growth. It could also inhibit fungal growth, unblock the vascular bundles and stomata, maintain a balance of material and energy exchange within the plant, and thus restore the damaged plant to its normal growth capacity. All the results will provide an adequate reference for the prevention and control of stem rot disease on peppers with thifluzamide.

Biological roles of soil microbial consortium on promoting safe crop production in heavy metal(loid) contaminated soil: A systematic review

Heavy metal(loid) (HM) pollution of agricultural soils is a growing global environmental concern that affects planetary health. Numerous studies have shown that soil microbial consortia can inhibit the accumulation of HMs in crops. However, our current understanding of the effects and mechanisms of inhibition is fragmented. In this review, we summarise extant studies and knowledge to provide a comprehensive view of HM toxicity on crop growth and development at the biological, cellular and the molecular levels. In a meta-analysis, we find that microbial consortia can improve crop resistance and reduce HM uptake, which in turn promotes healthy crop growth, demonstrating that microbial consortia are more effective than single microorganisms. We then review three main mechanisms by which microbial consortia reduce the toxicity of HMs to crops and inhibit HMs accumulation in crops: 1) reducing the bioavailability of HMs in soil (e.g. biosorption, bioaccumulation and biotransformation); 2) improving crop resistance to HMs (e.g. facilitating the absorption of nutrients); and 3) synergistic effects between microorganisms. Finally, we discuss the prospects of microbial consortium applications in simultaneous crop safety production and soil remediation, indicating that they play a key role in sustainable agricultural development, and conclude by identifying research challenges and future directions for the microbial consortium to promote safe crop production.

Effects of microcystin-LR on purification efficiency of simulating drinking water source by Hydrocharis dubia (Bl.) backer

The safety of drinking water source directly affects human health. Microcystin-LR (MC-LR), a toxic and common pollutant in drinking water source, is released by algae and can impede the in-situ remediation effect of aquatic plant. Finding out the effect mechanism of MC-LR on the purification of drinking water by aquatic plant is the key to its application. This study aims to explore the performance and mechanism of MC-LR on drinking water source purification by Hydrocharis dubia (Bl.) backer. The optimum removal efficiency of NH4+-N, TP and COD were 90.7%, 93.2% and 77.3% at MC-LR concentration of 0.5 μg L-1, respectively. With the increase of MC-LR concentration, the pollutants removal rate was obviously inhibited causing by concentration-dependent. Furthermore, the growth and development of the Hydrocharis dubia (Bl.) backer roots were significantly promoted at the concentration of 0.1 μg L-1. The length, tips, surface area, and average diameter of the root increased by 71.3%, 271.4%, 265.5%, and 113.0%, respectively. Chlorophyll contents under low-concentration MC-LR show a 14.5%-15.7% promoting effect compared with the control group. The activities of POD and CAT were also stimulated with the MC-LR increasing (<1.0 μg L-1). Notably, the MDA contents increased with increasing MC-LR concentration (p < 0.01). This study indicates the effect mechanism of MC-LR on Hydrocharis dubia (Bl.) backer purification performance relies on the increased growth and enzyme activity of Hydrocharis dubia (Bl.) backer.

Adesmia pinifolia, a Native High-Andean Species, as a Potential Candidate for Phytoremediation of Cd and Hg

This study highlights Adesmia pinifolia, a native high-Andean species, as a potential candidate for the phytoremediation of soils contaminated with Cd and Hg. In this work, a semi-hydronic assay with different doses of Cd (3, 4.5, and 6 mg L-1) and Hg (0.8, 1.2, and 1.6 mg L-1) was analysed to evaluate the establishment of plants, antioxidant defence systems, oxidative stress, and the ability to accumulate heavy metals. The results indicate high survival rates (>80%); however, Cd significantly reduced shoot and root biomass, while Hg increased root biomass with the 1.6 mg L-1 treatment. Cd and Hg tend to accumulate more in roots (2534.24 µg/g and 596.4 µg g-1, respectively) compared to shoots (398.53 µg g-1 and 140.8 µg g-1, respectively). A significant decrease in the bioconcentration factor of Cd and Hg in roots was observed as metal levels increased, reaching the maximum value at 3 mg L-1 (805.59 ± 54.38) and 0.8 mg L-1 (804.54 ± 38.09). The translocation factor, <1 for both metals, suggests that translocation from roots to shoots is limited. An overproduction of reactive oxygen species (ROS) was observed, causing lipid peroxidation and oxidative damage to plant membranes. Tolerance strategies against subsequent toxicity indicate that enhanced glutathione reductase (GR) activity and glutathione (GSH) accumulation modulate Cd and Hg accumulation, toxicity, and tolerance.

Multiple Physiological and Biochemical Functions of Ascorbic Acid in Plant Growth, Development, and Abiotic Stress Response

Ascorbic acid (AsA) is an important nutrient for human health and disease cures, and it is also a crucial indicator for the quality of fruit and vegetables. As a reductant, AsA plays a pivotal role in maintaining the intracellular redox balance throughout all the stages of plant growth and development, fruit ripening, and abiotic stress responses. In recent years, the de novo synthesis and regulation at the transcriptional level and post-transcriptional level of AsA in plants have been studied relatively thoroughly. However, a comprehensive and systematic summary about AsA-involved biochemical pathways, as well as AsA's physiological functions in plants, is still lacking. In this review, we summarize and discuss the multiple physiological and biochemical functions of AsA in plants, including its involvement as a cofactor, substrate, antioxidant, and pro-oxidant. This review will help to facilitate a better understanding of the multiple functions of AsA in plant cells, as well as provide information on how to utilize AsA more efficiently by using modern molecular biology methods.

Comparative Analysis of the Effect of Gamma-, Electron, and Proton Irradiation on Transcriptomic Profile of Hordeum vulgare L. Seedlings: In Search for Molecular Contributors to Abiotic Stress Resilience

The development of adaptation strategies for crops under ever-changing climate conditions is a critically important food security issue. Studies of barley responses to ionising radiation showed that this evolutionarily ancient stress factor can be successfully used to identify molecular pathways involved in adaptation to a range of abiotic stressors. In order to identify potential molecular contributors to abiotic stress resilience, we examined the transcriptomic profiles of barley seedlings after exposure to γ-rays, electrons, and protons. A total of 553 unique differentially expressed genes with increased expression and 124 with decreased expression were detected. Among all types of radiation, the highest number of differentially expressed genes was observed in electron-irradiated samples (428 upregulated and 56 downregulated genes). Significant upregulation after exposure to the three types of radiation was shown by a set of ROS-responsive genes, genes involved in DNA repair, cell wall metabolism, auxin biosynthesis and signalling, as well as photosynthesis-related genes. Most of these genes are known to be involved in plant ROS-mediated responses to other abiotic stressors, especially with genotoxic components, such as heavy metals and drought. Ultimately, the modulation of molecular pathways of plant responses to ionising radiation may be a prospective tool for stress tolerance programmes.

The role of epigenetic and epitranscriptomic modifications in plants exposed to non-essential metals

Contamination of the soil with non-essential metals and metalloids is a serious problem in many regions of the world. These non-essential metals and metalloids are toxic to all organisms impacting crop yields and human health. Crop plants exposed to high concentrations of these metals leads to perturbed mineral homeostasis, decreased photosynthesis efficiency, inhibited cell division, oxidative stress, genotoxic effects and subsequently hampered growth. Plants can activate epigenetic and epitranscriptomic mechanisms to maintain cellular and organism homeostasis. Epigenetic modifications include changes in the patterns of cytosine and adenine DNA base modifications, changes in cellular non-coding RNAs, and remodeling histone variants and covalent histone tail modifications. Some of these epigenetic changes have been shown to be long-lasting and may therefore contribute to stress memory and modulated stress tolerance in the progeny. In the emerging field of epitranscriptomics, defined as chemical, covalent modifications of ribonucleotides in cellular transcripts, epitranscriptomic modifications are postulated as more rapid modulators of gene expression. Although significant progress has been made in understanding the plant's epigenetic changes in response to biotic and abiotic stresses, a comprehensive review of the plant's epigenetic responses to metals is lacking. While the role of epitranscriptomics during plant developmental processes and stress responses are emerging, epitranscriptomic modifications in response to metals has not been reviewed. This article describes the impact of non-essential metals and metalloids (Cd, Pb, Hg, Al and As) on global and site-specific DNA methylation, histone tail modifications and epitranscriptomic modifications in plants.

Synergistic effects of exogenous glutathione and calcium on ascorbate-glutathione cycle and glutathione-associated enzymes upregulation under lead stress in Brassica napus L

Heavy metals (HMs) such as lead (Pb) pose a significant threat to global food security due to their adverse effect on the health of crop plants. Calcium (Ca) and Glutathione (GSH) are signaling molecules to scavenge free radicals in HM-stressed plants. In this study, GSH and Ca's role is examined in supporting canola seedlings against Pb toxicity. In a pot experiment, the administration of Glutathione (GSH, 0 and 100 µM) and/or calcium (CaCl2, 0 and 500 µM) in canola seedlings was examined under lead stress (0 and 100 µM of Pb(NO3)2. Compared with the control samples, Pb treatment increased MDA and H2O2 values by 61 and 53%, respectively, indicative of oxidative burst. However, using a combination of GSH and Ca lowered oxidative stress in Pb-stressed plants by an approximately twofold reduction in MDA and H2O2 content. Total PC content increased by 78% in Pb-stressed plants, suggesting that these chelating peptides diminish the damaging effects of Pb. Interestingly, further boosts in total PC levels were recorded in Pb-stressed plants treated with GSH and Ca concurrently. The addition of exogenous GSH and Ca to Pb-stressed canola plants limited Pb uptake and translocation and improved ascorbate-glutathione cycle performance. Moreover, compared to their separate usage, the co-treatment of exogenous GSH and Ca strengthened the GSH pool by increasing the activities of enzymes involved in GSH metabolism. The findings demonstrate that exogenous GSH and Ca modulate GSH synthesis, metabolism, and redox homeostasis synergistically to enhance resistance to oxidative stress generated by Pb.

Dose dependent effect of nitrogen on the phyto extractability of Cd in metal contaminated soil using Wedelia trilobata

Cadmium (Cd) is one of the toxic heavy metal that negatively affect plant growth and compromise food safety for human consumption. Nitrogen (N) is an essential macronutrient for plant growth and development. It may enhance Cd tolerance of invasive plant species by maintaining biochemical and physiological characteristics during phytoextraction of Cd. A comparative study was conducted to evaluate the phenotypical and physiological responses of invasive W. trilobata and native W. chinensis under low Cd (10 µM) and high Cd (80 µM) stress, along with different N levels (i.e., normal 91.05 mg kg-1 and low 0.9105 mg kg-1). Under low-N and Cd stress, the growth of leaves, stem and roots in W. trilobata was significantly increased by 35-23%, 25-28%, and 35-35%, respectively, compared to W. chinensis. Wedelia trilobata exhibited heightened antioxidant activities of catalase and peroxidase were significantly increased under Cd stress to alleviate oxidative stress. Similarly, flavonoid content was significantly increased by 40-50% in W. trilobata to promote Cd tolerance via activation of the secondary metabolites. An adverse effect of Cd in the leaves of W. chinensis was further verified by a novel hyperspectral imaging technology in the form of normalized differential vegetation index (NDVI) and photochemical reflectance index (PRI) compared to W. trilobata. Additionally, W. trilobata increased the Cd tolerance by regulating Cd accumulation in the shoots and roots, bolstering its potential for phytoextraction potential. This study demonstrated that W. trilobata positively responds to Cd with enhanced growth and antioxidant capabilities, providing a new platform for phytoremediation in agricultural lands to protect the environment from heavy metals pollution.

Integration of Physiological, Transcriptomic and Metabolomic Reveals Molecular Mechanism of Paraisaria dubia Response to Zn2+ Stress

Utilizing mycoremediation is an important direction for managing heavy metal pollution. Zn²⁺ pollution has gradually become apparent, but there are few reports about its pollution remediation. Here, the Zn²⁺ remediation potential of Paraisaria dubia, an anamorph of the entomopathogenic fungus Ophiocordyceps gracilis, was explored. There was 60% Zn²⁺ removed by Paraisaria dubia mycelia from a Zn²⁺-contaminated medium. To reveal the Zn²⁺ tolerance mechanism of Paraisaria dubia, transcriptomic and metabolomic were executed. Results showed that Zn²⁺ caused a series of stress responses, such as energy metabolism inhibition, oxidative stress, antioxidant defense system disruption, autophagy obstruction, and DNA damage. Moreover, metabolomic analyses showed that the biosynthesis of some metabolites was affected against Zn²⁺ stress. In order to improve the tolerance to Zn²⁺ stress, the metabolic mechanism of metal ion transport, extracellular polysaccharides (EPS) synthesis, and microcycle conidiation were activated in P. dubia. Remarkably, the formation of microcycle conidiation may be triggered by reactive oxygen species (ROS) and mitogen-activated protein kinase (MAPK) signaling pathways. This study supplemented the gap of the Zn²⁺ resistance mechanism of Paraisaria dubia and provided a reference for the application of Paraisaria dubia in the bioremediation of heavy metals pollution.

Hexaploid Salix rehderiana is more suitable for remediating lead contamination than diploids, especially male plants

Willows are promising candidates for phytoremediation, but the lead (Pb) phytoremediation potential of different willow ploidy and sex has not yet been exploited. In this study, the Pb uptake, translocation and detoxification capacities of hexaploid and diploid, female and male Salix rehderiana were investigated. The results showed that Pb treatment inhibited biomass accumulation and gas exchange, caused ultrastructural and oxidative damage, and induced antioxidant, phytohormonal and transcriptional regulation in S. rehderiana. Absorbed Pb was mainly accumulated in the roots with restricted root-to-shoot transport. Despite lower biomass, greater transpiration, phytohormonal and transcriptional regulation indicated that hexaploid S. rehderiana had higher tissue Pb concentration, total accumulated Pb amount (4.39 mg, 6.19 mg, 6.60 mg and 10.83 mg in diploid and hexaploid females and males, respectively) as well as bioconcentration factors and translocation factors (0.412, 0.593, 0.921 and 1.320 for bioconcentration factors in roots, and 0.029, 0.032, 0.035 and 0.047 for translocation factors in diploid and hexaploid females and males, respectively) than diploids. Higher soil urease and acid phosphatase activities also favored hexaploids to use more available N and P than diploids in Pb-contaminated soils. Additionally, hexaploid S. rehderiana had stronger antioxidant, phytohormonal and transcriptional responses, and displayed less morphological and ultrastructural damage than diploids after Pb treatment, suggesting that hexaploids have greater Pb uptake, translocation and detoxification capacities than diploids. Moreover, S. rehderiana males had greater Pb uptake and translocation abilities, as well as stronger antioxidant, phytohormonal, and transcriptional regulation mediated Pb detoxification capacities than females. Therefore, hexaploid S. rehderiana are superior to diploids, and males are better than females in Pb phytoremediation. This study provides novel and valuable insights for selecting better willow materials to mitigate Pb contamination.

Interactive effects of polystyrene microplastics and Pb on growth and phytochemicals in mung bean (Vigna radiata L.)

Interaction of different pollutants can aggravate hazards to biotic components in agroecosystems. Microplastics (MPs) are especially needed to be focused on because of their increasing use in life around the globe. We investigated the interactive impacts of polystyrene microplastics (PS-MP) and lead (Pb) on mung bean (Vigna radiata L.). Toxicity of MPs and Pb directly impeded V. radiata attributes. In combination i.e., M2P2 (40 µM Pb + 4.0 mg L-1 MPs) predominantly reduced the shoot root fresh and dry weights. \ Pb and PS-MP impaired the Rubisco activity and chlorophyll contents. The dose dependent relationship (M2P2) discomposed indole 3-acetic acid by 59.02%. Individual treatments P2 (40 µM Pb) and M2 (4.0 mg L^-1 MPs) respectively instigated a decline (44.07% and 27.12%) in IBA, while ABA was elevated. M2 significantly enhanced the contents of Alanine (Ala), Arginine (Arg), Proline (Pro), and glycine (Gly) by 64.11%, 63%, and 54% compared to control. Lysine (Lys) and Valine (Val) presented a converse relationship with other amino acids. Except for control, a gradual decline in yield parameters were observed in individual and combined applications of PS-MP. Proximate composition of carbohydrates, lipids and proteins also reflected a clear decrease in these compounds after combined application of Pb and MPs. Although, individual doses caused a decline in these compounds but effect of combined doses Pb and PS-MP was highly significant. Our results demonstrated the toxicity effect of Pb and MP in V. radiata attributes that is mainly linked with cumulative physiological and metabolic perturbations. These collective negative impacts of different doses of MPs and Pb on V. radiata would certainly pose serious implications for humans.

Potential of plant species adapted to semi-arid conditions for phytoremediation of contaminated soils

Physical and chemical remediation techniques used in contaminated areas are expensive and damaging to the soil structure. Biological alternatives, such as phytoremediation, are economical and applicable to large areas. The main limitation of phytoremediation is identifying plants that are both capable of stabilizing and/or absorbing metals from soil and adapted to edaphoclimatic conditions of the contaminated areas. The objective of this study is to evaluate the ability of plant species adapted to Brazilian semi-arid conditions to grow in soils contaminated with Pb. A greenhouse experiment was carried out in a 4 × 5 factorial: four plant species (M. oleifera, P. juliflora, A. peregrina, and U. ruziziensis) and five Pb concentrations in soil (0.0; 0.52; 1.05; 2.10, and 4.20 g kg^-1). All species grew at all Pb levels, but only P. juliflora and A. peregrina did not exhibit significant reductions in most growth variables. U. ruziziensis, despite showing reductions in growth variables, was the species with the highest dry matter accumulation in both shoots and roots, in addition to accumulating higher amounts of Pb. We conclude that the species P. juliflora, A. peregrina and U. ruziziensis are more suitable for cultivation in soils containing high levels of Pb.

Biochar and nano-ferric oxide synergistically alleviate cadmium toxicity of muskmelon

Cadmium is toxic to plants. The accumulation of cadmium in edible plants such as muskmelon may affect the safe production of crops and result in human health problem. Thus effective measures are urgently needed for soil remediation. This work aims to investigate the effects of nano-ferric oxide and biochar alone or mixture on muskmelon under cadmium stress. The results of growth and physiological indexes showed that compared with the application of cadmium alone, the composite treatment (biochar and nano-ferric oxide) decreased malondialdehyde content by 59.12% and ascorbate peroxidase activity increased by 276.6%. Their addition can increase the stress resistance of plants. The results of soil analysis and cadmium content determination in plants showed that the composite treatment was beneficial to reduce the cadmium content in various parts of muskmelon. In the presence of high concentration of cadmium, the Target Hazard Quotient value of peel and flesh of muskmelon in the composite treatment was less than 1, which means the edible risk was greatly reduced. Furthermore, the addition of composite treatment increased the content of effective components; the contents of polyphenols, flavonoids, and saponins in the flesh of the compound treatment were increased by 99.73%, 143.07%, and 18.78% compared with the cadmium treatment. The results provide a technical reference for the further application of biochar combined with nano-ferric oxide in the field of soil heavy metal remediation, and provide a theoretical basis for further research on reducing the toxicity of cadmium to plants and improving the edible quality of crops.

Transcriptome modulation by endophyte drives rice seedlings response to Pb stress

This study investigated the growth, SPAD value, chlorophyll fluorescence and transcriptome response of endophyte uninoculated and inoculated rice seedlings under Pb stress after treatment of 1 d and 5 d. Inoculation of endophytes significantly improved the plant height, SPAD value, F_v/F_0, F_v/F_m and PI_ABS by 1.29, 1.73, 0.16, 1.25 and 1.90 times on the 1 d, by 1.07, 2.45, 0.11, 1.59 and 7.90 times on the 5 d, respectively, however, decreased the root length by 1.11 and 1.65 times on the 1 d and 5 d, respectively under Pb stress. Analysis of rice seedlings leaves by RNA-seq, there were 574 down-regulated and 918 up-regulated genes after treatment of 1 d, 205 down-regulated and 127 up-regulated genes after treatment of 5 d, of which 20 genes (11 up-regulated and 9 down-regulated) exhibited the same changing pattern after treatment of 1 d and 5 d. Using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) to annotate these DEGs, and it was found that many of DEGs involved in photosynthesis, oxidative detoxification, hormone synthesis and signal transduction, protein phosphorylation/kinase and transcription factors. These findings provide new insights into the molecular mechanism of interaction between endophyte and plants under heavy metal stress, and contribute to agricultural production in limited environments.

Phytoremediation Competence of Composite Heavy-Metal-Contaminated Sediments by Intercropping Myriophyllum spicatum L. with Two Species of Plants

A variety of remediation approaches have been applied to reduce the harm and diffusion of heavy metals in aquatic sediments; however, phytoremediation in co-contaminated soils is still not clear. In order to explore the phytoremediation of sediments contaminated by Cu and Pb, two submerged plants with different characteristics, Vallisneria natans and Hydrilla verticillata, were interplanted with Myriophyllum spicatum. By simulating a submerged plant ecological environment, medium-scale-simulated ecological remediation experiments were carried out. The results showed that the two planting patterns were effective in repairing the sediments in the Cu and Pb contaminated sediments. The intercropping of Myriophyllum spicatum and Vallisneria natans can be used as the plant stabilizer of Cu because of the TF > 1 and BCF < 1, and the intercropping with Hydrilla verticillata can regulate the enrichment efficiency of Myriophyllum spicatum. The removal rates of Cu and Pb in sediments reached 26.1% and 68.4%, respectively, under the two planting patterns. The risk grade of the restored sediments was RI < 150, indicating a low risk.

Cell selection to increase lawn grass resistance to lead pollution

Lead is one of the priority soil pollutants among heavy metals. To increase the species diversity of ecosystems, it is necessary to increase the resistance of plants to lead. The aim of the work was to obtain plants resistant to lead. The objects of our study were to lawn grasses. The effect of lead on the growth and regenerative ability of calli was determined. The results of this work showed that lead is less toxic to calli than copper. Biotechnological method for obtaining lead resistant plants has been developed. The effect of lead on the growth of regenerants and original plants was determined. Agrostis stolonifera plants that are obtained after cell selection have demonstrated a high degree of resistance to lead. Can the developed technology be used for other lawn grasses? We obtained lead resistant plants Festuca rubra. Therefore, using cell selection can increase the tolerance of lawn grasses to lead.

The high pH value of alkaline salt destroys the root membrane permeability of Reaumuria trigyna and leads to its serious physiological decline

Variable climatic conditions frequently have harmful effects on plants. Reaumuria trigyna, a salt-secreting xerophytic shrub, occurs in Inner Mongolia, which has a poor environment for plant growth. To explore the physiological and molecular mechanisms of R. trigyna in response to environmental stress, this study investigated the abiotic resistance of R. trigyna in terms of growth regulation, antioxidant defense, osmotic regulation, ion transport, and ion homeostasis-related genes. R. trigyna seedlings were treated with 400 mM NaCl, 400 mM neutral salts (NaCl:Na₂SO₄ = 9:1), 50 mM alkaline salts (NaHCO₃:Na₂CO₃ = 9:1), 10% polyethylene glycol (PEG), and UV-B. Seedlings under 400 mM NaCl and 400 mM neutral salt stress showed less damage. While alkaline salt, PEG, and UV stress caused more damage, specifically in oxidative damage, proline levels, electrolyte leakage, and activation of antioxidant defenses. Furthermore, under the abiotic stress treatments, the accumulation of Na⁺ increased while the accumulation of K⁺ decreased. Further analysis showed that the flow rate of Na⁺ and K⁺ under alkaline salt stress was higher than under neutral salt stress. Neutral salt induced high expression of RtNHX1 and RtSOS1, while alkaline salt induced high expression of RtHKT1, and alkaline salt stress significantly reduced the activity of root cells. These results indicated that R. trigyna seedlings were more tolerant to neutral than alkaline salts; this might be because root activity decreased at high pH levels, which impaired membrane permeability and the ion transfer system, leading to an imbalance between Na⁺ and K⁺, and in turn to excessive accumulation of reactive oxygen species (ROS) and decreased plant stress resistance.

Proteomic analysis of T. qataranse exposed to lead (Pb) stress reveal new proteins with potential roles in Pb tolerance and detoxification mechanism

Soil lead (Pb) contamination is one of the environmental problems facing the modern world. Sources of Pb in soil include industrial activities such as mining and smelting processes, agricultural activities such as application of insecticide and municipal sewage sludges, and urban activities such as use of lead in gasoline, paints, and other materials. Phytoremediation is the direct use of living green plants and is an effective, cheap, non-invasive, and environmentally friendly technique used to transfer or stabilize all the toxic metals and environmental pollutants in polluted soil or groundwater. Current work in this area is invested in elucidating mechanisms that underpin toxic-metal tolerance and detoxification mechanisms. The present study aims to gain insight into the mechanisms of Pb tolerance in T. qataranse by comparative proteomics. MALDI-TOF/MS and in silico proteome analysis showed differential protein expression between treated (50 mg kg^⎯1 Pb) and untreated (0 mg kg^⎯1 Pb) T. qataranse. A total of eighty-six (86) differentially expressed proteins, most of which function in ion and protein binding, antioxidant activity, transport, and abiotic response stress, were identified. In addition, essential stress-regulating metabolic pathways, including glutathione metabolism, cellular response to stress, and regulation of HSF1-mediated heat shock response, were also enriched. Also, at 52- and 49-kDa MW band areas, up to six hypothetical proteins with unknown functions were identified. Of these, protein AXX17_AT2G26660 is highly rich in glycine amino acid residues (up to 76%), suggesting that it is a probable glycine-rich protein (GRP) member. Although GRPs are known to be involved in plant defense against abiotic stress, including salinity and drought, there is no report on their role on Pb tolerance and or detoxification in plants. Further enrichment analysis in the current study reveals that the hypothetical proteins do not interact with known proteins and are not part of any enriched pathway. However, additional research is needed to functionally validate the role of the identified proteins in Pb detoxification mechanism.

Metabolic engineering of the violacein biosynthetic pathway toward a low-cost, minimal-equipment lead biosensor

Metabolic engineered bacteria have been successfully employed to produce various natural colorants, which are expected to be used as the visually recognizable signals to develop mini-equipment biological devices for monitoring toxic heavy metals. The violacein biosynthetic pathway has been reconstructed in Escherichia coli (E. coli). Here the successful production of four violacein derivatives was achieved by integrating metabolic engineering and synthetic biology. Lead binding to the metalloregulator enables whole-cell colorimetric biosensors capable of assessing bioavailable lead. Deoxyviolacein-derived signal showed the most satisfied biosensing properties among prodeoxyviolacein (green), proviolacein (blue), deoxyviolacein (purple), and violacein (navy). The limit of detection (LOD) of pigment-based biosensors was 2.93 nM Pb(II), which is lower than that of graphite furnace atomic absorption spectrometry. Importantly, a good linear dose-response model in a wide dose range (2.93-6000 nM) was obtained in a non-cytotoxic deoxyviolacein-based biosensor, which was significantly better than cytotoxic violacein-based biosensor (2.93-750 nM). Among ten metal ions, only Cd(II) and Hg(II) exerted a slight influence on the response of the deoxyviolacein-based biosensor toward Pb(II). The deoxyviolacein-based biosensor was validated in detecting bioaccessible Pb(II) in environmental samples. Factors such as low cost and minimal-equipment requirement make this biosensor a suitable biological device for monitoring toxic lead in the environment.

Insights into site-specific influences of emission sources on accumulation of heavy metal(loid)s in soils by wheat grains

Excessive accumulation of heavy metal(loid)s in agricultural environment usually originates from anthropogenic activities. Both large diversities of emission sources and complexity of plant accumulation challenge the understanding of the site-specific effects of emission sources on heavy metal(loid)s in wheat grains. Herein, both soil samples and wheat grain samples (n = 80) were collected from the farmland of Jiyuan City, China. Soil and grain burdens of heavy metal(loid)s were determined by inductively coupled plasma mass spectrometry (ICP-MS) and/or X-ray fluorescence spectrometry (XRF). The quotients (Q) were developed to indicate relative impacts of industrial plants and traffic to soil sites. Principal component analysis-absolute principal component scores-multivariate linear regression (PCA-APCS-MLR) analysis was conducted to reveal the source contributions to heavy metal(loid)s in grains, considering Q values, soil, and wheat grain data. Results showed that contributions of main sources and factors drastically varied with soil sites, and usually overlapped to different extents. For grain Cd and grain Pb, natural soil silicate (0.066/0.104 mg/kg) and iron-bearing minerals (- 0.044/ - 0.174 mg/kg) contributed to high extents, while metal smelting activities (0.018/0.019 mg/kg) and agronomic activities (- 0.017/ - 0.019 mg/kg) unexpectedly posed low or moderate contributions. The pH-mediated availability of soil Cd (0.035 mg/kg) and the sand-dust weather (0.028 mg/kg) also made considerable contributions to grain Cd. For grain As, both natural soil iron-bearing (- 0.048 mg/kg) and silicate minerals (- 0.013 mg/kg) made negative contributions. The results benefit to the decision-making of pollution remediation of farmland soils in the regional scales.

Sulfur metabolism, organic acid accumulation and phytohormone regulation are crucial physiological processes modulating the different tolerance to Pb stress of two contrasting poplars

To investigate the pivotal physiological processes modulating lead (Pb) tolerance capacities of poplars, the saplings of two contrasting poplar species, Populus × canescens with high Pb sensitivity and Populus nigra with relatively low Pb sensitivity, were treated with either 0 or 8 mM Pb for 6 weeks. Lead was absorbed by the roots and accumulated massively in the roots and leaves, leading to overproduction of reactive oxygen species, reduced photosynthesis and biomass in both poplar species. Particularly, the tolerance index of P. × canescens was significantly lower than that of P. nigra. Moreover, the physiological responses including the concentrations of nutrient elements, thiols, organic acids, phytohormones and nonenzymatic antioxidants, and the activities of antioxidative enzymes in the roots and leaves were different between the two poplar species. Notably, the differences in concentrations of nutrient elements, organic acids and phytohormones were remarkable between the two poplar species. A further evaluation of the Pb tolerance-related physiological processes showed that the change of 'sulfur (S) metabolism' in the roots was greater, and that of 'organic acid accumulation' in the roots and 'phytohormone regulation' in the leaves were markedly smaller in P. × canescens than those in P. nigra. These results suggest that there are differences in Pb tolerance capacities between P. × canescens and P. nigra, which is probably associated with their contrasting physiological responses to Pb stress, and that S metabolism, organic acid accumulation and phytohormone regulation are probably the key physiological processes modulating the different Pb tolerance capacities between the two poplar species.

Low-molecular-weight organic acid-mediated tolerance and Pb accumulation in centipedegrass under Pb stress

Lead (Pb) is one of the most harmful, toxic pollutants to the ecological environment and humans. Centipedegrass, a fast-growing warm-season turfgrass, is excellent for Pb pollution remediation. Exogenous low-molecular-weight organic acid (LMWOA) treatment is a promising approach for assisted phytoremediation. However, the effects of this treatment on the tolerance and Pb accumulation of centipedegrass are unclear. This study investigated these effects on the physiological growth response and Pb accumulation distribution characteristics of centipedegrass. Applications of 400 μM citric acid (CA), malic acid (MA) and tartaric acid (TA) significantly reduced membrane lipid peroxidation levels of leaves and improved biomass production of Pb-stressed plants. These treatments mainly increased peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) activities and enhanced free protein (Pro), ascorbic acid (AsA) and phytochelatins (PCs) contents, ultimately improving the Pb tolerance of centipedegrass. Their promoting effects decreased as follows: TA>CA>MA. All the treatments decreased root Pb concentrations and increased stem and leaf Pb concentrations, thus increasing total Pb accumulation and TF values. MA had the best and worst effects on Pb accumulation and Pb transportation, respectively. CA had the best and worst effects on Pb transportation and Pb accumulation, respectively. TA exhibited strong effects on both Pb accumulation and transport. Furthermore, all treatments changed the subcellular Pb distribution patterns and distribution models of the chemical forms of Pb in each tissue. The root Pb concentration was more highly correlated with the Pb subcellular fraction distribution pattern, while the stem and leaf Pb concentrations were more highly correlated with the distribution models of the chemical forms of Pb. Overall, TA improved plant Pb tolerance best and promoted both Pb absorption and transportation well and is considered the best candidate for Pb-contaminated soil remediation with centipedegrass. This study provides a new idea for Pb-contaminated soil remediation with centipedegrass combined with LMWOAs.

LncRNA PMAT-PtoMYB46 module represses PtoMATE and PtoARF2 promoting Pb2+ uptake and plant growth in poplar

Lead (Pb²⁺) is one of the most toxic heavy-metal contaminants. Fast-growing woody plants with substantial biomass are ideal for bioremediation. However, the transcriptional regulation of Pb²⁺ uptake in woody plants remains unclear. Here, we identified 226 Pb²⁺-induced, differentially expressed long non-coding RNAs (DELs) in Populus tomentosa. Functional annotation revealed that these DELs mainly regulate carbon metabolism, biosynthesis of secondary metabolites, energy metabolism, and signal transduction through their potential target genes. Association and epistasis analysis showed that the lncRNA PMAT (Pb²⁺-induced multidrug and toxic compound extrusion (MATE) antisense lncRNA) interacts epistatically with PtoMYB46 to regulate leaf dry weight, photosynthesis rate, and transketolase activity. Genetic transformation and molecular assays showed that PtoMYB46 reduces the expression of PtoMATE directly or indirectly through PMAT, thereby reducing the secretion of citric acid (CA) and ultimately promoting Pb²⁺ uptake. Meanwhile, PtoMYB46 targets auxin response factor 2 (ARF2) and reduces its expression, thus positively regulating plant growth. We concluded that the PMAT-PtoMYB46-PtoMATE-PtoARF2 regulatory module control Pb²⁺ tolerance, uptake, and plant growth. This study demonstrates the involvement of lncRNAs in response to Pb²⁺ in poplar, yielding new insight into the potential for developing genetically improved woody plant varieties for phytoremediating lead-contaminated soils.

Adaptation of the Invasive Plant (Sphagneticola trilobata L. Pruski) to a High Cadmium Environment by Hybridizing With Native Relatives

Invasive species can evolve rapidly in the invasion areas to adapt to new habitats. Sphagneticola trilobata L. Pruski, an invasive species, was studied for its tolerance to cadmium (Cd) in the soil and compared with its natural hybrid. From the perspective of photosynthetic physiology, antioxidant characteristics, and leaf hormone levels, the differences between the leaves of the two species before and after Cd treatment were compared. The results showed that the hybrid had stronger tolerance to Cd stress than invasive species. After Cd stress, the indexes of gas-exchange [net photosynthetic rate (Pn), intercellular CO₂ concentration (Ci), stomatal conductance (Gs), and transpiration rate (Tr)] of the hybrid was higher than invasive species, while the content of non-enzymatic antioxidants (flavonoids and total phenols) and antioxidant enzyme activities [peroxidase (POD) and superoxide dismutase (SOD)] was lower in hybrid than in invasive species. The changes in the content of plant hormones [auxin (IAA) and abscisic acid (ABA)] under Cd stress showed that hybrid can still maintain growth and prevent leaf senescence. Furthermore, the differences in gene expression between hybrid and invasive species in photosynthetic physiology, the antioxidant capacity of leaves, and endogenous hormone (IAA and ABA) synthesis pathway also showed that hybrid has stronger Cd tolerance than invasive species. This suggests that invasive species will realize the invasion through hybridization with the native relatives to overcome the stress from environmental factors. The study implied that hybridization between invasive species and native relatives is an important way for invasive species to spread in a wider and new environment that invasive species have not experienced in the area of origin.

Evaluation of Physiological and Biochemical Parameters and Some Bioindicators of Barium Tolerance in Limbarda crithmoides and Helianthus annuus

Soils and water resources of our ecosystems may contain Barium (Ba), a toxic metal naturally existent in the Earth’s crust and also can be derived from recycled wastes produced of several anthropogenic activities. As a result of this fact, the accumulation of Ba in agriculture soils would increase to reach the crops and eventually end up in the human food chain. The purpose of this work was to study tolerance and accumulation abilities in Limbarda crithmoides and Helianthus annuus treated with increasing concentrations of barium (from 0 to 500 µM) for 45 days. In order to evaluate the response of these species to Ba stress, the biomass production, the water status, and the accumulation of the secondary metabolites, macronutrients, total inorganic nitrogen (TIN), and Ba in shoots and roots, as well as chlorophyll levels, and metal tolerance index of the entire plant were assessed. Results showed an increase in plant biomass production and tolerance index in the two species with increasing Ba concentration. A significant increase in polyphenols and flavonoids levels was also shown with no negative effect on the macronutrients and TIN; however, the latter were found reduced in roots of L. crithmoides. Chlorophylls also were not affected. An average of 3000 µg·g−1 DW of Ba was accumulated in each organ of L. crithmoides while H. annuus accumulated up to 1350 µg·g−1 DW in the shoots. Our findings proved that L. crithmoides and H. annuus were susceptible to tolerate Ba-induced stress with high levels of Ba accumulation in the aboveground parts as well as in the roots during the 45 days of the experiments.

Understanding the Phytoremediation Mechanisms of Potentially Toxic Elements: A Proteomic Overview of Recent Advances

Potentially toxic elements (PTEs) such as cadmium (Cd), lead (Pb), chromium (Cr), and arsenic (As), polluting the environment, pose a significant risk and cause a wide array of adverse changes in plant physiology. Above threshold accumulation of PTEs is alarming which makes them prone to ascend along the food chain, making their environmental prevention a critical intervention. On a global scale, current initiatives to remove the PTEs are costly and might lead to more pollution. An emerging technology that may help in the removal of PTEs is phytoremediation. Compared to traditional methods, phytoremediation is eco-friendly and less expensive. While many studies have reported several plants with high PTEs tolerance, uptake, and then storage capacity in their roots, stem, and leaves. However, the wide application of such a promising strategy still needs to be achieved, partly due to a poor understanding of the molecular mechanism at the proteome level controlling the phytoremediation process to optimize the plant's performance. The present study aims to discuss the detailed mechanism and proteomic response, which play pivotal roles in the uptake of PTEs from the environment into the plant's body, then scavenge/detoxify, and finally bioaccumulate the PTEs in different plant organs. In this review, the following aspects are highlighted as: (i) PTE's stress and phytoremediation strategies adopted by plants and (ii) PTEs induced expressional changes in the plant proteome more specifically with arsenic, cadmium, copper, chromium, mercury, and lead with models describing the metal uptake and plant proteome response. Recently, interest in the comparative proteomics study of plants exposed to PTEs toxicity results in appreciable progress in this area. This article overviews the proteomics approach to elucidate the mechanisms underlying plant's PTEs tolerance and bioaccumulation for optimized phytoremediation of polluted environments.

Iron Oxide and Silicon Nanoparticles Modulate Mineral Nutrient Homeostasis and Metabolism in Cadmium-Stressed Phaseolus vulgaris

The application of nanoparticles (NPs) has been proved as an efficient and promising technique for mitigating a wide range of stressors in plants. The present study elucidates the synergistic effect of iron oxide nanoparticles (IONPs) and silicon nanoparticles (SiNPs) in the attenuation of Cd toxicity in Phaseolus vulgaris. Seeds of P. vulgaris were treated with IONPs (10 mg/L) and SiNPs (20 mg/L). Seedlings of uniform size were transplanted to pots for 40 days. The results demonstrated that nanoparticles (NPs) enhanced growth, net photosynthetic rate, and gas exchange attributes in P. vulgaris plants grown in Cd-contaminated soil. Synergistic application of IONPs and SiNPs raised not only K+ content, but also biosynthesis of polyamines (PAs), which alleviated Cd stress in P. vulgaris seedlings. Additionally, NPs decreased malondialdehyde (MDA) content and electrolyte leakage (EL) in P. vulgaris plants exposed to Cd stress. These findings suggest that stress alleviation was mainly attributed to the enhanced accumulation of K+ content, improved antioxidant defense system, and higher spermidine (Spd) and putrescine (Put) levels. It is suggested that various forms of NPs can be applied synergistically to minimize heavy metal stress, thus increasing crop production under stressed conditions.

Single Molecular Chelation Dynamics Reveals That DNA Has a Stronger Affinity toward Lead(II) than Cadmium(II)

Lead ions can bind to DNA via nonelectrostatic interactions and hence alter its structure, which may be related to their adverse effects. The dynamics of Pb²⁺-DNA interaction has not been well understood. In this study, we report the monomolecular dynamics of the Pb²⁺-DNA interaction using a magnetic tweezers (MT) setup. We found that lead cations could induce DNA compaction at ionic strengths above 1 μM, which was also confirmed by morphology characterization. The chelation behavior of the Pb²⁺-DNA and the Cd²⁺-DNA complex solutions after adding EDTA were compared. The results showed that EDTA chelated with the bound metal ions on DNA and consequently led to restoring the DNA to its original length but with different restoration speeds for the two solutions. The fast binding dynamics and the slower chelation dynamics of the Pb²⁺ scenario compared to that of Cd²⁺ suggested that Pb²⁺ was more capable to induce DNA conformational change and that the Pb²⁺-DNA complex was more stable than the Cd²⁺-DNA complex. The stronger affinities for DNA bases and the inner binding of lead cations were two possible causes of the dynamics differences. Three agents, including EDTA, sodium gluconate, and SDBS, were used to remove the bound lead ions on DNA. It was shown that EDTA was the most efficient, and sodium gluconate could not fully restore DNA from its compact state. We concluded that both EDTA and SDBS were good candidates to restore the Pb²⁺-bound DNA to its original state.

Oxidative RNA Modifications as an Early Response of Soybean (Glycine max L.) Exposed to Copper and Lead

Plant exposure to metals is associated with the accumulation of reactive oxygen species, which mediate the oxidation of various molecules including lipids, proteins, and nucleic acids. The aim of the present study is the evaluation of the impact of short-term Cu and Pb treatment on oxidative events in the roots of soybean seedlings, with special emphasis on RNA oxidation. The results show that an increase in total RNA oxidative modification, 8-hydroxyguanosine (8-OHG), constitutes a very early response to both applied metals, observed already within the first hour of treatment. Exposure to Cu and Pb resulted also in the increase in superoxide anion and hydrogen peroxide levels and intensified lipid peroxidation. However, these responses were most prominent after longer treatment times. On the other hand, no changes were observed in the level of protein carbonylation. It can be concluded that 8-OHG enrichment in total RNA constitutes one of the earliest reactions to metals, which precedes the symptoms of oxidative stress.

Genome-Wide Association Study Reveals Complex Genetic Architecture of Cadmium and Mercury Accumulation and Tolerance Traits in Medicago truncatula

Heavy metals are an increasing problem due to contamination from human sources that and can enter the food chain by being taken up by plants. Understanding the genetic basis of accumulation and tolerance in plants is important for reducing the uptake of toxic metals in crops and crop relatives, as well as for removing heavy metals from soils by means of phytoremediation. Following exposure of Medicago truncatula seedlings to cadmium (Cd) and mercury (Hg), we conducted a genome-wide association study using relative root growth (RRG) and leaf accumulation measurements. Cd and Hg accumulation and RRG had heritability ranging 0.44 - 0.72 indicating high genetic diversity for these traits. The Cd and Hg trait associations were broadly distributed throughout the genome, indicated the traits are polygenic and involve several quantitative loci. For all traits, candidate genes included several membrane associated ATP-binding cassette transporters, P-type ATPase transporters, oxidative stress response genes, and stress related UDP-glycosyltransferases. The P-type ATPase transporters and ATP-binding cassette protein-families have roles in vacuole transport of heavy metals, and our findings support their wide use in physiological plant responses to heavy metals and abiotic stresses. We also found associations between Cd RRG with the genes CAX3 and PDR3, two linked adjacent genes, and leaf accumulation of Hg associated with the genes NRAMP6 and CAX9. When plant genotypes with the most extreme phenotypes were compared, we found significant divergence in genomic regions using population genomics methods that contained metal transport and stress response gene ontologies. Several of these genomic regions show high linkage disequilibrium (LD) among candidate genes suggesting they have evolved together. Minor allele frequency (MAF) and effect size of the most significant SNPs was negatively correlated with large effect alleles being most rare. This is consistent with purifying selection against alleles that increase toxicity and abiotic stress. Conversely, the alleles with large affect that had higher frequencies that were associated with the exclusion of Cd and Hg. Overall, macroevolutionary conservation of heavy metal and stress response genes is important for improvement of forage crops by harnessing wild genetic variants in gene banks such as the Medicago HapMap collection.

Bioimaging of Pb by LA-ICP-MS and Pb isotopic compositions reveal distributions and origins of Pb in wheat grain

Atmospheric heavy metal deposition in agroecosystems has increased recently, especially in northern China, which poses serious risks to crop safety and human health via food chain. Wheat grains can accumulate high levels of Pb even when wheat is planted in soils with low levels of Pb. However, the influence of atmospheric deposition on the accumulation and distribution of Pb in wheat grain is still unclear. A field survey was conducted in three districts (A: a district with industrial and traffic pollution; B: a district with traffic pollution; and C: an unpolluted district) in Hebei Province, North China. The grain of wheat cultivated in district A accumulated more Pb from soil and atmospheric deposition than those in other districts, and the bran from district A contained 3.50 and 2.04 times more Pb than those from districts B and C, respectively. The Pb distribution pattern in wheat grain detected by laser ablation inductively coupled mass spectrometry (LA-ICP-MS) was characterized by accumulation mostly in the pericarp and seed coat rather than in the crease, embryo and endosperm. Furthermore, Pb isotopic data showed that airborne Pb was the major source (>50%) of Pb in wheat grain. Interestingly, average contributions of Pb from atmospheric deposition to white flour (78.22%) were higher than its contributions to bran (56.27%). In addition, wheat flag leaves were exposed to PbSO₄ at the booting stage, and much greater Pb accumulation (0.33-0.48 mg/kg) was observed in exposed wheat grain than in the control (P < 0.05), PbSO₄ constituted most (82.80-100%) of the Pb in the wheat grain. In summary, the results confirmed the efficient foliar Pb uptake and transfer from atmospheric deposition into wheat grain. It would be a new sight for understanding the contribution of airborne Pb to Pb accumulation in wheat grains.

Physiological and Gene Expression Responses of Six Annual Ryegrass Cultivars to Cobalt, Lead, and Nickel Stresses

Heavy metals negatively affect soil quality and crop growth. In this study, we compared the tolerance of six ryegrass cultivars to cobalt (Co²⁺), lead (Pb²⁺), and nickel (Ni²⁺) stresses by analyzing their physiological indexes and transcript levels of genes encoding metal transporters. Compared with the other cultivars, the cultivar Lm1 showed higher germination rates and better growth under Co²⁺, Pb²⁺, or Ni²⁺ treatments. After 48 h of Co²⁺ treatment, the total antioxidant capacity of all six ryegrass cultivars was significantly increased, especially that of Lm1. In contrast, under Pb²⁺ stress, total antioxidant capacity of five cultivars was significantly decreased, but that of Lm1 was unaffected at 24 h. Staining with Evans blue dye showed that the roots of Lm1 were less injured than were roots of the other five ryegrass cultivars by Co²⁺, Pb²⁺, and Ni²⁺. Lm1 translocated and accumulated lesser Co²⁺, Pb²⁺, and Ni²⁺ than other cultivars. In Lm1, genes encoding heavy metal transporters were differentially expressed between the shoots and roots in response to Co²⁺, Pb²⁺, and Ni²⁺. The aim of these researches could help find potential resource for phytoremediation of heavy metal contamination soil. The identified genes related to resistance will be useful targets for molecular breeding.

Lead content in soil, plants, rodents, and amphibians in the vicinity of a heating plant's ash waste

This study supplements previous research focused on environmental condition in the vicinity of waste ash material. The main aim of our study was the comparative analysis of lead levels in soil, plant, and animal organisms in the area of the tailings pond and surroundings, using x-ray. Findings confirm that the level of Pb in the top layer of soil is in the range of 20-135 ppm. Lead content in Calamagrostis plant tissues was confirmed only at the tailings pond area, with the highest lead concentrations measured in above-ground components; stems with blooms followed by roots and ground floor sheats. The livers, kidneys, and hearts of Apodemus flavicollis were examined, with findings of higher values in the tailings pond area than in the reference site, and average values of 14.5 ppm for livers, 16.0 ppm for kidneys, and 16.6 ppm for hearts. No significant differences were discovered based on sex and body length/body weight of A. flavicollis individuals. Values for Bombina variegata liver tissue reached an average of 12.3 ppm for individuals caught in a water reservoir without ash sediments, versus 15.7 ppm in those trapped by the edge of then tailings pond area. Females had lower concentrations of lead than males, but with no statistically significant differences found. Despite lower lead levels in soil and ash than expected, concentrations in mammalian and amphibian organs suggest a possible transition of this element into the food chain, and therefore further research in this area is recommended.

Lead speciation and availability affected by plants in a contaminated soil

Changes in lead (Pb) speciation in the rhizosphere may be plant species-dependent and dictate Pb fate and behavior in the soil-plant system. X-ray absorption near edge structure (XANES) spectroscopy can explain how these changes affect Pb availability in soils and its uptake by plants. We investigated the changes in Pb speciation and availability in the rhizosphere of eucalypt (Eucalyptus urophylla x Eucalyptus grandis), palisade grass (Urochloa brizantha cv. Marandu), and Indian mustard (Brassica juncea L.) using XANES spectroscopy. A greenhouse experiment was performed in a complete randomized design, with three plant species and a no plant control treatment. After three months, rhizosphere and bulk soil samples were collected, Pb speciation was assessed by Pb L₃-edge XANES spectroscopy, and Pb concentration was determined in plant tissue. In bulk soil, we found Pb primarily as Pb-Il (Pb sorbed to illite; 48%) and lead monoxide (PbO; 36%). In the rhizosphere, Pb-Ka (Pb sorbed to kaolinite; 33-56%) and (CH₃COO)₂Pb (25-41%) were the main Pb forms, the latter suggesting Pb complexation by low molecular weight organic acids (LMWOAs). Palisade grass rhizospheric soil had a lower abundance of Pb-Ka and a higher abundance of (CH₃COO)₂Pb than eucalypt and mustard, which led to low Pb concentration in plant tissue. LMWOAs exudation followed by Pb²⁺ complexation is the apparent mechanism used by palisade grass to detoxify the rhizosphere and control Pb uptake. Given its low Pb uptake and potential to complex Pb in organic forms, palisade grass may be a promising species for Pb phytostabilization in contaminated soils.

Contribution of the flag leaf to lead absorption in wheat grain at the grain-filling stage

Wheat flag leaf (FL) is one of the primary sources of carbohydrates in grains; however, its role in grain lead (Pb) absorption remains unclear. A field experiment was conducted to assess the relative contribution of the FL to Pb accumulation in wheat grain by two contrasting treatments: without (CK) and with FL removal (FLR) at the grain-filling stage. The Pb concentration in leaves was closely related to leaf strata and decreased from FL to the third leaf. FLR treatment significantly reduced the yield and grain Pb concentration by 2.79% and 11.47%, respectively. The contribution of FL to grain Pb accumulation decreased gradually with the filling process, from 35.08% (at early stage) to 13.94% (at maturity stage). After FLR, the contribution proportion of atmospheric fallout to grain Pb decreased from 69.01% (CK) to 62.43% (FLR). Combined isotope analysis with scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) revealed that the main contribution of FLs to grain Pb originated from Pb fallout in fine atmospheric particles. Therefore, taking measures to reduce the influence of fine atmospheric particles on wheat may be an effective way to control wheat grain Pb contamination.