Effect of lead on root growth

Augmentation of physiology and productivity, and reduction of lead accumulation in lettuce grown in lead contaminated soil by rhizobacteria-assisted rhizoengineeing

Microbial-assisted rhizoengineering is a promising biotechnology for improving crop productivity. In this study, lettuce roots were bacterized with two lead (Pb) tolerant rhizobacteria including Pseudomonas azotoformans ESR4 and P. poae ESR6, and a consortium consisted of ESR4 and ESR6 to increase productivity, physiology and antioxidants, and reduce Pb accumulation grown in Pb-contaminated soil i.e., 80 (Pb in native soil), 400 and 800 mg kg-1 Pb. In vitro studies showed that these strains and the consortium produced biofilms, synthesized indole-3-acetic acid and NH3, and solubilized phosphate challenging to 0, 100, 200 and 400 mg L-1 of Pb. In static conditions and 400 mg L-1 Pb, ESR4, ESR6 and the consortium adsorbed 317.0, 339.5 and 357.4 mg L-1 Pb, respectively, while 384.7, 380.7 and 373.2 mg L-1 Pb, respectively, in shaking conditions. Fourier transform infrared spectroscopy results revealed that several functional groups [Pb-S, M - O, O-M-O (M = metal ions), S-S, PO, CO, -NH, -NH2, C-C-O, and C-H] were involved in Pb adsorption. ESR4, ESR6 and the consortium-assisted rhizoengineering (i) increased leaf numbers and biomass production, (ii) reduced H2O2 production, malondialdehyde, electrolyte leakages, and transpiration rate, (iii) augmented photosynthetic pigments, photosynthetic rate, water use efficiency, total antioxidant capacity, total flavonoid content, total phenolic content, and minerals like Ca2+ and Mg2+ in comparison to non-rhizoengineering plants grown in Pb-contaminated soil. Principal component analysis revealed that higher pigment production and photosynthetic rate, improved water use efficiency and increased uptake of Ca2+ were interlinked to increased productivity by bacterial rhizoengineering of lettuce grown in different levels of Pb exposures. Surprisingly, Pb accumulation in lettuce roots and shoots was remarkably decreased by rhizoengineering than in non-rhizoengineering. Thus, these bacterial strains and this consortium could be utilized to improve productivity and reduce Pb accumulation in lettuce.

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.

Effect of intercropping and biochar amendments on lead removal capacity by Corchorus olitorius and Zea mays

Intercropping is a sustainable strategy recognized for boosting crop production and mitigating heavy metal toxicity in contaminated soils. This study investigates the effects of biochar amendments on Pb-contaminated soil, utilizing monocropping and intercropping techniques with C. olitorius and Z. mays. The research assesses Pb removal capacity, nutrient uptake, antioxidant enzymes, and soil Pb fractionation. In monocropping, the phytoremediation ratio for C. olitorius increased from 16.67 to 27.33%, while in intercropping, it rose from 19.00 to 28.33% with biochar amendments. Similarly, Z. mays exhibited an increased phytoremediation ratio from 53.33 to 74.67% in monocropping and from 63.00 to 78.67% in intercropping with biochar amendments. Intercropping significantly increased the peroxidase (POD) activity in Z. mays roots by 22.53%, and there were notable increases in shoot POD of C. olitorius (11.54%) and Z. mays (16.20%) with biochar application. CAT showed consistent improvements, increasing by 37.52% in C. olitorius roots and 74.49% in Z. mays roots with biochar. Biochar amendments significantly increased N content in soil under sole cropping of Z. mays and intercropping systems. In contrast, Cu content increased by 56.34%, 59.05%, and 79.80% in monocropping (C. olitorius and Z. mays) and intercropping systems, respectively. This suggests that biochar enhances nutrient availability, improving phytoremediation efficacy in Pb-contaminated soil. Phyto availability of trace metals (Zn, Mn, Cu, and Fe) exhibited higher levels with biochar amendments than those without. The findings indicate that intercropping and biochar amendments elevate antioxidant enzyme levels, reducing reactive oxygen species and mitigating Pb toxicity effects. This approach improves phytoremediation efficiency and holds promise for soil pollution remediation while enhancing nutrient content and crop quality in Pb-contaminated soil.

Multicontamination Toxicity Evaluation in the Model Plant Lactuca sativa L

Many contaminated soils contain several toxic elements (TEs) in elevated contents, and plant-TE interactions can differ from single TE contamination. Therefore, this study investigated the impact of combined contamination (As, Cd, Pb, Zn) on the physiological and metabolic processes of lettuce. After 45 days of exposure, TE excess in soil resulted in the inhibition of root and leaf biomass by 40 and 48%, respectively. Oxidative stress by TE accumulation was indicated by markers-malondialdehyde and 5-methylcytosine-and visible symptoms of toxicity (leaf chlorosis, root browning) and morpho-anatomical changes, which were related to the change in water regime (water potential decrease). An analysis of free amino acids (AAs) indicated that TEs disturbed N and C metabolism, especially in leaves, increasing the total content of free AAs and their families. Stress-induced senescence by TEs suggested changes in gas exchange parameters (increase in transpiration rate, stomatal conductance, and intercellular CO2 concentration), photosynthetic pigments (decrease in chlorophylls and carotenoids), a decrease in water use efficiency, and the maximum quantum yield of photosystem II. These results confirmed that the toxicity of combined contamination significantly affected the processes of lettuce by damaging the antioxidant system and expressing higher leaf sensitivity to TE multicontamination.

Suillusgrevillei and Suillus luteus promote lead tolerance of Pinus tabulaeformis and biomineralize lead to pyromorphite

Lead (Pb) is a hazardous heavy metal that accumulates in many environments. Phytoremediation of Pb polluted soil is an environmentally friendly method, and a better understanding of mycorrhizal symbiosis under Pb stress can promote its efficiency and application. This study aims to evaluate the impact of two ectomycorrhizal fungi (Suillus grevillei and Suillus luteus) on the performance of Pinus tabulaeformis under Pb stress, and the biomineralization of metallic Pb in vitro. A pot experiment using substrate with 0 and 1,000 mg/kg Pb2+ was conducted to evaluate the growth, photosynthetic pigments, oxidative damage, and Pb accumulation of P. tabulaeformis with or without ectomycorrhizal fungi. In vitro co-cultivation of ectomycorrhizal fungi and Pb shots was used to evaluate Pb biomineralization. The results showed that colonization by the two ectomycorrhizal fungi promoted plant growth, increased the content of photosynthetic pigments, reduced oxidative damage, and caused massive accumulation of Pb in plant roots. The structural characteristics of the Pb secondary minerals formed in the presence of fungi demonstrated significant differences from the minerals formed in the control plates and these minerals were identified as pyromorphite (Pb5(PO4)3Cl). Ectomycorrhizal fungi promoted the performance of P. tabulaeformis under Pb stress and suggested a potential role of mycorrhizal symbiosis in Pb phytoremediation. This observation also represents the first discovery of such Pb biomineralization induced by ectomycorrhizal fungi. Ectomycorrhizal fungi induced Pb biomineralization is also relevant to the phytostabilization and new approaches in the bioremediation of polluted environments.

Melatonin Mitigates Lead-Induced Oxidative Stress and Modifies Phospholipid Profile in Tobacco BY-2 Suspension Cells

Many studies have shown that melatonin (an indoleamine) is an important molecule in plant physiology. It is known that this indoleamine is crucial during plant stress responses, especially by counteracting secondary oxidative stress (efficient direct and indirect antioxidant) and switching on different defense plant strategies. In this report, we present exogenous melatonin's potential to protect lipid profile modification and membrane integrity in Nicotiana tabacum L. line Bright Yellow 2 (BY-2) cell culture exposed to lead. There are some reports of the positive effect of melatonin on animal cell membranes; ours is the first to report changes in the lipid profile in plant cells. The experiments were performed in the following variants: LS: cells cultured on unmodified LS medium-control; (ii) MEL: BY-2 cells cultured on LS medium with melatonin added from the beginning of culture; (iii) Pb: BY-2 cells cultured on LS medium with Pb2+ added on the 4th day of culture; (iv) MEL+Pb: BY-2 cells cultured on LS medium with melatonin added from the start of culture and stressed with Pb2+ added on the 4th day of culture. Lipidomic analysis of BY-2 cells revealed the presence of 40 different phospholipids. Exposing cells to lead led to the overproduction of ROS, altered fatty acid composition and increased PLD activity and subsequently elevated the level of phosphatidic acid at the cost of dropping the phosphatidylcholine. In the presence of lead, double-bond index elevation, mainly by higher quantities of linoleic (C18:2) and linolenic (C18:3) acids in the log phase of growth, was observed. In contrast, cells exposed to heavy metal but primed with melatonin showed more similarities with the control. Surprisingly, the overproduction of ROS caused of lipid peroxidation only in the stationary phase of growth, although considerable changes in lipid profiles were observed in the log phase of growth-just 4 h after lead administration. Our results indicate that the pretreatment of BY-2 with exogenous melatonin protected tobacco cells against membrane dysfunctions caused by oxidative stress (lipid oxidation), but also findings on a molecular level suggest the possible role of this indoleamine in the safeguarding of the membrane lipid composition that limited lead-provoked cell death. The presented research indicates a new mechanism of the defense strategy of plant cells generated by melatonin.

Role of the molecular structure of humified organic matter in rice plant response to environmental lead pollution

Humified organic matter has been shown to decrease Pb toxicity in plants. However, there are still gaps in our understanding of the mechanism by which this phenomenon occurs. In this study, we aimed to assess the ability of humic substances (HSs), humic acids (HAs), and fulvic acids (FAs) to enhance defense mechanisms in rice plants under lead (Pb)-stressed conditions. HS fractions were isolated from vermicompost using the chemical fractionation methodology established by the International Humic Substances Society. These fractions were characterized by solid-state NMR and FTIR. Chemometric analysis was used to compare humic structures and correlate them with bioactivity. Three treatments were tested to evaluate the protective effect of humic fractions on rice plants. The first experiment involved the application of humic fractions along with Pb. The second comprised pretreatment with humic fractions followed by subsequent exposure to Pb stress. The third experiment involved Pb stress and subsequent treatment with humic fractions. The root morphology and components of the antioxidative defense system were evaluated and quantified. The results showed that HS + Pb, HA + Pb, and FA + Pb treatment preserved root growth and reduced the levels of O2- and malondialdehyde (MDA) in the roots by up to 5% and 2%, respectively. Pretreatment of the plants with humic fractions promoted the maintenance of root growth and reduced the contents of O2-, H2O2, and MDA by up to 48%, 22%, and 20%, respectively. Combined application of humic fractions and Pb reduced the Pb content in plant tissues by up to 60%, while pretreatment reduced it by up to 80%. The protective capacity of humic fractions is related to the presence of peptides, lignin, and carbohydrate fragments in their molecular structures. These results suggest that products could be developed that can mitigate the adverse effects of heavy metals on agricultural crops.

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.

Metabolomics reveals the phytotoxicity mechanisms of foliar spinach exposed to bulk and nano sizes of PbCO3

PbCO3 is an ancient raw material for Pb minerals and continues to pose potential risks to the environment and human health through mining and industrial processes. However, the specific effects of unintentional PbCO3 discharge on edible plants remain poorly understood. This study unravels how foliar application of PbCO3 induces phytotoxicity by potentially influencing leaf morphology, photosynthetic pigments, oxidative stress, and metabolic pathways related to energy regulation, cell damage, and antioxidant defense in Spinacia oleracea L. Additionally, it quantifies the resultant human health risks. Plants were foliarly exposed to PbCO3 nanoparticles (NPs) and bulk products (BPs), as well as Pb2+ at 0, 5, 10, 25, 50, and 100 mg·L-1 concentrations once a day for three weeks. The presence and localization of PbCO3 NPs inside the plant cells were confirmed by TEM-EDS analysis. The maximum accumulation of total Pb was recorded in the root (2947.77 mg·kg-1 DW for ion exposure), followed by the shoot (942.50 mg·kg-1 DW for NPs exposure). The results revealed that PbCO3 and Pb2+ exposure had size- and dose-dependent inhibitory effects on spinach length, biomass, and photosynthesis attributes, inducing impacts on the antioxidase activity of CAT, membrane permeability, and nutrient elements absorption and translocation. Pb2+ exhibited pronounced toxicity in morphology and chlorophyll; PbCO3 BP exposure accumulated the most lipid peroxidation products of MDA and H2O2; and PbCO3 NPs triggered the largest cell membrane damage. Furthermore, PbCO3 NPs at 10 and 100 mg·L-1 induced dose-dependent metabolic reprogramming in spinach leaves, disturbing the metabolic mechanisms related to amino acids, antioxidant defense, oxidative phosphorylation, fatty acid cycle, and the respiratory chain. The spinach showed a non-carcinogenic health risk hierarchy: Pb2+ > PbCO3 NPs > PbCO3 BPs, with children more vulnerable than adults. These findings enhance our understanding of PbCO3 particle effects on food security, emphasizing the need for further research to minimize their impact on human dietary health.

Phytotoxicity of trihalomethanes and trichloroacetic acid on Vigna radiata and Allium cepa plant models

Disinfection by-products (DBPs) are a concern due to their presence in chlorinated wastewater, sewage treatment plant discharge, and surface water, and their potential for environmental toxicity. Despite some attention to their ecotoxicity, little is known about the phytotoxicity of DBPs. This study aimed to evaluate the individual and combined phytotoxicity of four trihalomethanes (THMs: trichloromethane (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and tribromomethane (TBM) and their mixture (THM4)), and trichloroacetic acid (TCAA) using genotoxic and cytotoxic assays. The analysis included seed germination tests using Vigna radiata and root growth tests, mitosis studies, oxidative stress response, chromosomal aberrations (CA), and DNA laddering using Allium cepa. The results showed a progressive increase in root growth inhibition for both plant species as the concentration of DBPs increased. High concentrations of mixtures of four THMs resulted in significant (p < 0.05) antagonistic interactions. The effective concentration (EC50) value for V. radiata was 5655, 3145, 2690, 1465, 3570, and 725 mg/L for TCM, BDCM, DBCM, TBM, THM4, and TCAA, respectively. For A. cepa, the EC50 for the same contaminants was 700, 400, 350, 250, 450, and 105 mg/L, respectively. DBP cytotoxicity was observed through CAs, including C-metaphase, unseparated anaphase, lagging chromosome, sticky metaphase, and bridging. Mitotic depression (MD) increased with dose, reaching up to 54.4% for TCAA (50-500 mg/L). The electrophoresis assay showed DNA fragmentation and shearing, suggesting genotoxicity for some DBPs. The order of phytotoxicity for the tested DBPs was TCAA > TBM > DBCM > BDCM > THM4 > TCM. These findings underscore the need for further research on the phytotoxicity of DBPs, especially given their common use in agricultural practices such as irrigation and the use of sludge as manure.

Toxic effects of lead on plants: integrating multi-omics with bioinformatics to develop Pb-tolerant crops

MAIN CONCLUSION

Lead disrupts plant metabolic homeostasis and key structural elements. Utilizing modern biotechnology tools, it's feasible to develop Pb-tolerant varieties by discovering biological players regulating plant metabolic pathways under stress. Lead (Pb) has been used for a variety of purposes since antiquity despite its toxic nature. After arsenic, lead is the most hazardous heavy metal without any known beneficial role in the biological system. It is a crucial inorganic pollutant that affects plant biochemical and morpho-physiological attributes. Lead toxicity harms plants throughout their life cycle and the extent of damage depends on the concentration and duration of exposure. Higher levels of lead exposure disrupt numerous key metabolic activities of plants including oxygen-evolving complex, organelles integrity, photosystem II connectivity, and electron transport chain. This review summarizes the detrimental effects of lead toxicity on seed germination, crop growth, and yield, oxidative and ultra-structural alterations, as well as nutrient absorption, transport, and assimilation. Further, it discusses the Pb-induced toxic modulation of stomatal conductance, photosynthesis, respiration, metabolic-enzymatic activity, osmolytes accumulation, and antioxidant activity. It is a comprehensive review that reports on omics-based studies along with morpho-physiological and biochemical modifications caused by lead stress. With advances in DNA sequencing technologies, genomics and transcriptomics are gradually becoming popular for studying Pb stress effects in plants. Proteomics and metabolomics are still underrated and there is a scarcity of published data, and this review highlights both their technical and research gaps. Besides, there is also a discussion on how the integration of omics with bioinformatics and the use of the latest biotechnological tools can aid in developing Pb-tolerant crops. The review concludes with core challenges and research directions that need to be addressed soon.

Response of Carrot (Daucus carota L.) to Multi-Contaminated Soil from Historic Mining and Smelting Activities

A pot experiment was undertaken to investigate the effect of Cd, Pb and Zn multi-contamination on the physiological and metabolic response of carrot (Daucus carota L.) after 98 days of growth under greenhouse conditions. Multi-contamination had a higher negative influence on leaves (the highest Cd and Zn accumulation) compared to the roots, which showed no visible change in terms of anatomy and morphology. The results showed the following: (i) significantly higher accumulation of Cd, Zn, and Pb in the multi-contaminated variant (Multi) compared to the control; (ii) significant metabolic responses-an increase in the malondialdehyde content of the Multi variant compared to the control in the roots (by 20%), as well as in the leaves (by 53%); carotenoid content in roots decreased by 31% in the Multi variant compared with the control; and changes in free amino acids, especially those related to plant stress responses. The determination of hydroxyproline and sarcosine may reflect the higher sensitivity of carrot leaves to multi-contamination in comparison to roots. A similar trend was observed for the content of free methionine (significant increase of 31% only in leaves); (iii) physiological responses (significant decreases in biomass, changes in gas-exchange parameters and chlorophyll a); and (iv) significant changes in enzymatic activities (chitinase, alanine aminopeptidase, acid phosphatase) in the root zone.

Lead Toxicity-Mediated Growth and Metabolic Alterations at Early Seedling Stages of Maize (Zea mays L.)

To investigate the toxic effects of lead (Pb) on key metabolic activities essential for proper germination and seedling growth of maize seeds, experiments were carried out with different levels of Pb (0 to 120 mg of Pb L-1 as PbCl2) applied through growth medium to two maize hybrids H-3310S and H-6724. The research findings indicated that growth and metabolic activities were adversely affected by increased Pb contamination in growth medium; however, a slow increase in these parameters was recorded with increasing time from 0 to 120 h. Protease activity decreased with an increase in the level of Pb contamination but increased with time; consequently, a reduction in seed proteins and an increase in total free amino acids were observed with time. Similarly, α-amylase activity decreased with an increase in Pb concentration in growth medium while it increased with increasing time from 0 to 120 h; consequently, reducing and non-reducing sugars increased with time but decreased with exposure to lead. The roots of both maize hybrids had higher Pb contents than those of the shoot, which decreased the uptake of nitrogen, phosphorus, and potassium. All these nutrients are essential for optimal plant growth; therefore, the reduction in growth and biomass of maize seedlings could be due to Pb toxicity that altered metabolic processes, as sugar and amino acids are necessary for the synthesis of metabolic compounds, rapid cell division, and proper functioning of enzymes in the growing embryo, but all were dramatically reduced due to suppression of protease and α-amylase by toxicity of Pb. In general, hybrid H-3310S performed better in Pb-contaminated growth medium than H-6724.

Bioremediation of Heavy Metals by Rhizobacteria

Heavy elements accumulate rapidly in the soil due to industrial activities and the industrial revolution, which significantly impact the morphology, physiology, and yield of crops. Heavy metal contamination will eventually affect the plant tolerance threshold and cause changes in the plant genome and genetic structure. Changes in the plant genome lead to changes in encoded proteins and protein sequences. Consuming these mutated products can seriously affect human and animal health. Bioremediation is a process that can be applied to reduce the adverse effects of heavy metals in the soil. In this regard, bioremediation using plant growth-promoting rhizobacteria (PGPRs) as beneficial living agents can help to neutralize the negative interaction between the plant and the heavy metals. PGPRs suppress the adverse effects of heavy metals and the negative interaction of plant-heavy elements by different mechanisms such as biological adsorption and entrapment of heavy elements in extracellular capsules, reduction of metal ion concentration, and formation of complexes with metal ions inside the cell.

An analysis of differentially expressed and differentially m6A-modified transcripts in soybean roots treated with lead

Lead is one of the most common toxic heavy metal pollutants in nature, and exposure to lead can cause serious toxicity to many organisms. In this study, we collected root growth data from soybean plants exposed to lead for seven days and confirmed that lead significantly inhibited root growth. We performed a transcriptome-wide m6A methylation analysis to study the response of soybean RNA methylation groups to lead. The m6A modified regions were enriched near the 3'UTR region and stop codon, and m6A methylation was positively correlated with transcript abundance. In the presence of lead, the transcriptome range of m6A RNA methylation peaks increased, and we identified 1144 m6A modification peaks and 1094 differentially expressed genes. The integration of m6A methylation and transcriptomic results enabled us to identify 16 candidate genes whose transcripts were differentially methylated and differentially expressed under lead stress. Annotation results suggest that these genes may promote abiotic stress tolerance by impacting lead uptake, transport, and accumulation through ROS pathways, enzymes, transporters, and hormones. These results provide candidate genes for future studies of lead stress tolerance mechanisms in soybean roots and provide genetic resources for studying plant heavy metal stress in soybean breeding.

Health Risk and Quality Assessment of Vegetables Cultivated on Soils from a Heavily Polluted Old Mining Area

Three garden vegetables-radish, carrot and lettuce-were cultivated in a pot experiment using two soils from the Příbram area polluted mainly by cadmium (Cd), zinc (Zn), lead (Pb) and chromium (Cr). The soils of the Příbram district, Czech Republic, are heavily polluted as a result of the atmospheric deposition of toxic elements originating from historic lead-silver mining and smelting activities. The results showed that lettuce absorbed the highest amounts of toxic elements (Cd 28 and 30, Cr 12 and 13, Zn 92 and 205 mg·kg^-1 DW), except Pb, which was higher in radish (30 and 49 mg·kg^-1 DW). Changes in macronutrient contents in edible parts were not found, except for sulfur. A higher total free amino acids (fAAs) accumulation was shown in all vegetables in more contaminated soil, with the highest fAA content being in radish. A group of essential fAAs reached 7-24% of total fAAs in vegetables. The risk to human health was characterized using the target hazard quotient and total hazard index (HI). The cumulative effect of the consumption of vegetables with HI > 1 showed possible non-carcinogenic health effects for lettuce and carrot. HI decreased in the order Cd > Pb > Cr > Zn. The carcinogenic risk of toxic elements decreased in the order Cd > Cr > Pb (0.00054, 0.00026, 0.00003). These values showed a carcinogenic risk from the consumption of lettuce and carrot and confirmed that the adult population of the studied area is at high risk if lettuce and carrot cultivated in this area are consumed daily.

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.

Formation and characterization of leaf waste into organic compost

In solid waste management, pollution-free disposal of leaf waste in urban areas is still not standardized and adopted. According to the World Bank report, 57% of wastes generated in South East Asia are consisted of food and green waste, which can be recycled into valuable bio-compost. The present study shows a method of leaf litter waste management by composting it using essential microbe (EM) method. Different parameters, such as pH, electrical conductivity, macronutrients, micronutrients, and potentially toxic elements (PTE) were measured at zero to 50 days of composting using appropriate methods. The microbial composting was shown to mature within 20 to 40 days, and its maturity could be evaluated by the attainment of stable pH (8), electrical conductivity (0.9 mS/cm), and C:N ratio ≥ 20. The analysis was also performed on other bio-composts viz. kitchen waste compost, vermicompost, cow dung manure, municipal organic waste compost, and neem cake compost. The fertility index (FI) was evaluated based on six parameters viz. total carbon, total nitrogen, N ratio, phosphorus, potassium, and sulphur contents. The PTE values were used to calculate their clean index (CI). The results showed that leaf waste compost has a higher fertility index (FI = 4.06) than other bio-composts, except the neem cake compost (FI = 4.44). The clean index of the leaf waste compost (CI = 4.38) was also higher than other bio-composts. This indicates that leaf waste compost is a valuable bio-resource with high nutritive value and low PTE contamination, with a favourable prospective to be used in organic farming.

Assessing the effects of limestone dust and lead pollution on the ecophysiology of some selected urban tree species

Soil and air pollution caused by heavy metals and limestone dust are prevalent in urban environments and they are an alarming threat to the environment and humans. This study was designed to investigate the changes in morphological and physiological traits of three urban tree species seedlings (Bombax ceiba, Conocarpus lancifolius, and Eucalyptus camaldulensis) under the individual as well as synergetic effects of heavy metal lead (Pb) and limestone dust toxicities. The tree species were grown under controlled environmental conditions with nine treatments consisting of three levels of dust (0, 10, and 20 g) and three levels of Pb contaminated water irrigation (0, 5, and 10 mg L^-1). The results depicted that the growth was maximum in T₁ and minimum in T₉ for all selected tree species. B. ceiba performed better under the same levels of Pb and limestone dust pollution as compared with the other two tree species. The B. ceiba tree species proved to be the most tolerant to Pb and limestone pollution by efficiently demolishing oxidative bursts by triggering SOD, POD, CAT, and proline contents under different levels of lead and dust pollution. The photosynthetic rate, stomatal conductance, evapotranspiration rate, and transpiration rate were negatively influenced in all three tree species in response to different levels of lead and dust applications. The photosynthetic rate was 1.7%, 3.1%, 7.0%, 11.03%, 16.2%, 23.8%, 24.8%, and 30.7%, and the stomatal conductance was 5%, 10.5%, 23.5%, 40%, 50.01%, 61.5%, 75%, and 90.9%, greater in T₂, T₃, T₄, T₅, T₆, T₇, T₈, and T₉ plants of B. ceiba, respectively, as compared to T₁. Based on the findings, among these three tree species, B. ceiba is strongly recommended for planting in heavy metal and limestone dust-polluted areas followed by E. camaldulensis and C. lancifolius due to their better performance and efficient dust and heavy metal-scavenging capability.

Detoxifying the heavy metals: a multipronged study of tolerance strategies against heavy metals toxicity in plants

Heavy metal concentrations exceeding permissible limits threaten human life, plant life, and all other life forms. Different natural and anthropogenic activities emit toxic heavy metals in the soil, air, and water. Plants consume toxic heavy metals from their roots and foliar part inside the plant. Heavy metals may interfere with various aspects of the plants, such as biochemistry, bio-molecules, and physiological processes, which usually translate into morphological and anatomical changes. They use various strategies to deal with the toxic effects of heavy metal contamination. Some of these strategies include restricting heavy metals to the cell wall, vascular sequestration, and synthesis of various biochemical compounds, such as phyto-chelators and organic acids, to bind the free moving heavy metal ions so that the toxic effects are minimized. This review focuses on several aspects of genetics, molecular, and cell signaling levels, which integrate to produce a coordinated response to heavy metal toxicity and interpret the exact strategies behind the tolerance of heavy metals stress. It is suggested that various aspects of some model plant species must be thoroughly studied to comprehend the approaches of heavy metal tolerance to put that knowledge into practical use.

A genome-wide co-expression network analysis revealed ZmNRAMP6-mediated regulatory pathway involved in maize tolerance to lead stress

KEY MESSAGE

A metal transporter ZmNRAMP6 was identified by using a trait-associated co-expression network analysis at a genome-wide level. ZmNRAMP6 confers maize sensitivity to Pb by accumulating it to maize shoots. ZmNRAMP6 knockout detains Pb in roots, activates antioxidant enzymes, and improves Pb tolerance. Lead (Pb) is one of the most toxic heavy metal pollutants, which can penetrate plant cells via root absorption and thus cause irreversible damages to the human body through the food chain. To identify the key gene responsible for Pb tolerance in maize, we performed a trait-associated co-expression network analysis at a genome-wide level, using two maize lines with contrasting Pb tolerances. Finally, ZmNRAMP6 that encodes a metal transporter was identified as the key gene among the Pb tolerance-associated co-expression module. Heterologous expression of ZmNRAMP6 in yeast verified its role in Pb transport. Combined Arabidopsis overexpression and maize mutant analysis suggested that ZmNRAMP6 conferred plant sensitivity to Pb stress by mediating Pb distribution across the roots and shoots. Knockout of ZmNRAMP6 caused Pb retention in the roots and activation of the antioxidant enzyme system, resulting in an increased Pb tolerance in maize. ZmNRAMP6 was likely to transport Pb from the roots to shoots and environment. An integration of yeast one-hybrid and dual-luciferase reporter assay uncovered that ZmNRAMP6 was negatively regulated by a known Pb tolerance-related transcript factor ZmbZIP54. Collectively, knockout of ZmNRAMP6 will aid in the bioremediation of contaminated soil and food safety guarantee of forage and grain corn.

The Modification of Cell Wall Properties Is Involved in the Growth Inhibition of Rice Coleoptiles Induced by Lead Stress

Lead (Pb) is a widespread heavy metal pollutant that interferes with plant growth. In this study, we investigated the effects of Pb on the mechanical and chemical properties of cell walls and on the growth of coleoptiles of rice (Oryza sativa L.) seedlings grown in the air (on moistened filter paper) and underwater (submerged condition). Coleoptile growth of air-grown seedlings was reduced by 40% by the 3 mM Pb treatment, while that of water-grown ones was reduced by 50% by the 0.5 mM Pb. Although the effective concentration of Pb for growth inhibition of air-grown coleoptiles was much higher than that of water-grown ones, Pb treatment significantly decreased the mechanical extensibility of the cell wall in air- and water-grown coleoptiles, when it inhibited their growth. Among the chemical components of coleoptile cell walls, the amounts of cell wall polysaccharides per unit fresh weight and unit length of coleoptile, which represent the thickness of the cell wall, were significantly increased in response to the Pb treatment (3 mM and 0.5 mM Pb for air- and water-grown seedlings, respectively), while the levels of cell wall-bound diferulic acids (DFAs) and ferulic acids (FAs) slightly decreased. These results indicate that Pb treatment increased the thickness of the cell wall but not the phenolic acid-mediated cross-linking structures within the cell wall in air- and water-grown coleoptiles. The Pb-induced cell wall thickening probably causes the mechanical stiffening of the cell wall and thus decreases cell wall extensibility. Such modifications of cell wall properties may be associated with the inhibition of coleoptile growth. The results of this study provide a new finding that Pb-induced cell wall remodeling contributes to the regulation of plant growth under Pb stress conditions via the modification of the mechanical property of the cell wall.

The fate of secondary metabolites in plants growing on Cd-, As-, and Pb-contaminated soils-a comprehensive review

The study used scattered literature to summarize the effects of excess Cd, As, and Pb from contaminated soils on plant secondary metabolites/bioactive compounds (non-nutrient organic substances). Hence, we provided a systematic overview involving the sources and forms of Cd, As, and Pb in soils, plant uptake, mechanisms governing the interaction of these risk elements during the formation of secondary metabolites, and subsequent effects. The biogeochemical characteristics of soils are directly responsible for the mobility and bioavailability of risk elements, which include pH, redox potential, dissolved organic carbon, clay content, Fe/Mn/Al oxides, and microbial transformations. The radial risk element flow in plant systems is restricted by the apoplastic barrier (e.g., Casparian strip) and chelation (phytochelatins and vacuole sequestration) in roots. However, bioaccumulation is primarily a function of risk element concentration and plant genotype. The translocation of risk elements to the shoot via the xylem and phloem is well-mediated by transporter proteins. Besides the dysfunction of growth, photosynthesis, and respiration, excess Cd, As, and Pb in plants trigger the production of secondary metabolites with antioxidant properties to counteract the toxic effects. Eventually, this affects the quantity and quality of secondary metabolites (including phenolics, flavonoids, and terpenes) and adversely influences their antioxidant, antiinflammatory, antidiabetic, anticoagulant, and lipid-lowering properties. The mechanisms governing the translocation of Cd, As, and Pb are vital for regulating risk element accumulation in plants and subsequent effects on secondary metabolites.

Responses of Spring Barley to Zn- and Cd-Induced Stress: Morphometric Analysis and Cytotoxicity Assay

Heavy metals such as cadmium (Cd) and zinc (Zn) could be dangerous and pollute the environment due to their high migration ability, robust bioavailability, and acute toxicity to soil biota and plants. Considering the above characteristics of these elements, the study's aim was to explore the individual and combined impact of Cd and Zn contamination of Haplic Chernozem on growing two-row spring barley (Hordeum vulgare L.). The accumulation and distribution of Cd and Zn in various parts of H. vulgare have also been studied, which showed that Cd accumulation by H. vulgare occurred more intensely than that by Zn up to eight times. Cadmium and Zn suppress plant growth up to two times, more effect was noted by the combined impact of Cd and Zn. The study of plant morphological characteristics revealed that growth suppression and structural changes in the root and leaf tissues increased in proportion to Cd and Zn concentrations. Detailed analysis of the localizations of Zn and Cd in various organelles of H. vulgare cells was performed. Heavy metals change the ultrastructure of prominent energy-producing organelles in leaf cells, especially chloroplasts and mitochondria. Overall, the current findings offer insights into phytotoxicity induced by Cd and Zn individual application as well as in combination with the H. vulgare plant. Zinc showed protective effects against high doses of Cd under the combined application. These antagonistic interactions reduce their accessibility to H. vulgare. The present work can be useful in restricting the entry of these elements into the food chain and preventing creating a threat to human health.

Pfaffia glomerata is a hyperaccumulator candidate: Cd and Zn tolerance, absorption, transfer, and distribution

Pfaffia glomerata is a candidate for phytoremediation due to its high biomass and high bioaccumulation efficiency of multiple heavy metals. It is essential to further evaluate its tolerance, absorption, transfer, and distribution to multiple heavy metals. In the current study, we evaluated the tolerance, absorption, transfer, and distribution of P. glomerata in a Cd/Pb/Cu/Zn combined-contaminated environment by two hydroponic experiments. The results demonstrated that P. glomerata was not affected by Cd/Pb/Cu/Zn exposure, except for the 50 μM Cd/Pb/Cu/Zn treatment, which significantly decreased the stem biomass. In a single Cd, Pb, Cu, and Zn exposure, the root of P. glomerata absorbed Cd/Pb/Cu/Zn in the order of Cd > Zn > Pb > Cu. Almost all Pb and Cu accumulated in the plant roots and were hardly transferred to the aboveground parts. Therefore, the order of total Cd/Pb/Cu/Zn extraction of a single plant in multiple Cd/Pb/Cu/Zn exposures at the same concentration was Cd > Zn > Pb > Cu. The bioconcentration factor (BCF) of Cd and Zn in roots, stems, and leaves increased with the concentration of Cd and Zn in the solution, and was > 1. In contrast with Cd and Zn, the BCFs of Cu and Pb in the stems and leaves were < 1. The element distribution of Pb, Cu, Zn, and Mn in the stem of P. glomerata was dispersed, indicating that the stem of P. glomerata does not have a detoxification mechanism for distributing metals to the area of low biological activity. The total amount of tartaric acid, critic acid, and DOC secreted by P. glomerata roots decreased with the increase in Cd/Pb/Cu/Zn exposure. However, further investigation is needed to unravel the interaction between the LMWOAs secreted by the root of P. glomerata and heavy metals.

De Novo Transcriptome Assembly, Gene Annotations, and Characterization of Functional Profiling Reveal Key Genes for Lead Alleviation in the Pb Hyperaccumulator Greek Mustard (Hirschfeldia incana L.)

Lead (Pb) contamination is a widespread environmental problem due to its toxicity to living organisms. Hirschfeldia incana L., a member of the Brassicaceae family, commonly found in the Mediterranean regions, is characterized by its ability to tolerate and accumulate Pb in soils and hydroponic cultures. This plant has been reported as an excellent model to assess the response of plants to Pb. However, the lack of genomic data for H. incana hinders research at the molecular level. In the present study, we carried out RNA deep transcriptome sequencing (RNA-seq) of H. incana under two conditions, control without Pb(NO₃)₂ and treatment with 100 µM of Pb(NO₃)₂ for 15 days. A total of 797.83 million reads were generated using Illumina sequencing technology. We assembled 77,491 transcript sequences with an average length of 959 bp and N50 of 1330 bp. Sequence similarity analyses and annotation of these transcripts were performed against the Arabidopsis thaliana nr protein database, Gene Ontology (GO), and KEGG databases. As a result, 13,046 GO terms and 138 KEGG maps were created. Under Pb stress, 577 and 270 genes were differentially expressed in roots and aboveground parts, respectively. Detailed elucidation of regulation of metal transporters, transcription factors (TFs), and plant hormone genes described the role of actors that allow the plant to fine-tune Pb stress responses. Our study revealed that several genes related to jasmonic acid biosynthesis and alpha-linoleic acid were upregulated, suggesting these components’ implication in Hirschfeldia incana L responses to Pb stress. This study provides data for further genomic analyses of the biological and molecular mechanisms leading to Pb tolerance and accumulation in Hirschfeldia incana L.

Accidental lead in contaminated pipe-borne water and dietary furan intake perturbs rats' hepatorenal function altering oxidative, inflammatory, and apoptotic balance

Inadvertent exposure to furan and Pb is associated with hepatorenal abnormalities in humans and animals. It is perceived that these two chemical species may work in synergy to orchestrate liver and kidney damage. Against this background, we investigated the combined effect of furan and incremental lead (Pb) exposure on hepatorenal dysfunction. Wistar rats (n = 30; 150 g) were treated for 28 days accordingly: Control; FUR (8 mg/kg), PbAc (100 µg/L), FUR + PbAc₁ (8 mg/kg FUR + 1 µg/L PbAc); FUR + PbAc₁ (8 mg/kg FUR + 10 µg/L PbAc), and FUR + PbAc₁ (8 mg/kg FUR + 100 µg/L PbAc). Biomarkers of hepatorenal function, oxidative stress, inflammation, DNA damage, and apoptosis were examined. Furan and incrementally Pb exposure increased the levels of hepatorenal biomarkers and oxidative and pro-inflammatory mediators, including lipid peroxidation, reactive oxygen and nitrogen species, and interleukin-1 beta. Increased DNA damage, caspases- 9 and -3, and atypical histoarchitecture of the hepatorenal tissues exemplified furan and Pb treatment-related perturbations. Furthermore, the levels of antioxidants and IL-10 were also suppressed. Furan and Pb dose-dependently exacerbated hepatorenal derangements by altering the redox and inflammatory rheostats, worsened DNA damage, and related apoptotic onset that may potentiate hepatorenal disorders in humans and animals. The findings validate the synergistic effect of furan and Pb in the pathophysiology of kidney and liver disorders.

Potential pollution assessment of labile trace metals in Xixi River estuary sediments in Xiamen, China

The release of trace metals caused by industrial effluents and anthropogenic activities has been recorded in the Xixi River estuary, southern China. However, a thorough understanding of the behavior of trace heavy metals in Xixi River sediments is lacking. A total of 12 sediment cores were collected in June and December in the upper estuary section and mouth of the estuary. Here, an in situ high-resolution sampling technique, namely, diffusive gradients in thin films (DGT), was employed to acquire profiles of trace element concentrations and the release of bioavailable metals from sediments in different seasons. A three-step Community Bureau of Reference (BCR) sequential extraction method was used to explore the chemical speciation of trace metals in different seasons and to thereby assess the release potential of trace elements in sediments. The BCR sequential extraction results showed that the trace metals Fe, Mn, Co and Pb were mainly in the residual fraction, which rarely influences living organisms. The total mobile fractions (F1 + F2 + F3) of all trace metals were higher in winter than in summer, suggesting that accumulation occurred from summer to winter. DGT measurements showed that the intensity of sulfate reduction was higher in summer than in winter because of the high temperatures and high organic matter in summer. The intensity of sulfate and Mn(III/IV) reduction increased from the upper estuary section to the lower estuary. Fe(III) reduction decreased in summer but increased slowly in winter. The Pearson correlation results showed that the release of DGT-labile Co in pore water was related to Mn(III/IV) reduction, while the release of DGT-labile Pb was basically not controlled by the Fe-Mn-S redox transition. Abnormally high DGT-labile Pb concentrations were observed at the sampling station (XR3) closest to the estuary in winter, which might have been caused by the high Pb content in the local micro-sediments.

Lead-induced modification of growth and yield of Linum usitatissimum L. and its soil remediation potential

This study was designed to evaluate the pre-reproductive and reproductive responses of Linum usitatissimum L. (flax, linseed plant) to different levels of Pb in the soil. Flax seeds were sown in garden soil-filled earthen pots and treated with three different levels of lead as lead chloride (150, 450, and 750 mg Pb kg^-1 soil) except control, and each treatment was replicated three times. Growth and reproductive parameters and photosynthetic pigments were significantly reduced (p ≤ 0.05) for all treatments. Quantitatively, Chlorophyll b content decreased more than chlorophyll a and the amount of proline content in the leaves increased in lockstep with the increase of Pb levels in the soil. Pb was found in substantial amounts in the roots, shoots, and seeds. The pattern of Pb accumulation in different organs was root > shoot > seeds. Pb levels in seeds obtained from 750 mg Pb kg^-1 soil-treated plants exceeded the permissible limits. Biological concentration factor (BCF), biological accumulation coefficient (BAC) and translocation factor (TF) values showed that roots of L. usitatissimum absorbed and accumulated a substantial quantity of Pb but translocated only a fraction of that to the shoots. Therefore, L. usitatissimum L. can be used in phytostabilization rather than phytoextraction of Pb.

Seed Priming with ZnO and Fe3O4 Nanoparticles Alleviate the Lead Toxicity in Basella alba L. through Reduced Lead Uptake and Regulation of ROS

The increased lead (Pb) content in the environment has an impact on all living beings, including plant growth and quality. The present study aims to investigate the protective roles of zinc (Zn)- and iron (Fe)- nanoparticles (NPs) in alleviating stress symptoms caused by lead (Pb) exposure in Basella alba seedlings. For this purpose, 15 different treatment combinations of seed priming with two NPs at 0 and 200 mg L−1, and five Pb levels (0, 4, 8, 15, 20 mM) were chosen. Pb stress (20 mM) was found to reduce seed germination by 72.8% and seedling growth, particularly root length, by 92% when compared to the control. Under different Pb concentrations, seed priming with ZnNPs (200 mg L−1) and FeNPs (200 mg L−1) increased seed germination by 34.7% and 54.9%, respectively, and root length by 152.9% and 252.9%, respectively. In 20 mM Pb stress, NPs primed seedling showed decrease in Pb content by 33.7% with ZnNPs and 32.6% with FeNPs. Increased Pb stress resulted in increased reactive oxygen species (ROS) generation (H2O2) and lipid peroxidation (MDA) compared to non-Pb stressed seedlings. However, increased antioxidants in the NPs treatments such as SOD, CAT, POD and proline content, scavenged these ROS. Considering all the parameters under study, priming alleviated Pb stress in the following order: FeNPs > ZnNPs > hydropriming > control. To summarise, seed priming with Zn- and Fe-NPs has the potential to alleviate Pb toxicity via reduced Pb uptake, ROS generation and lipid peroxidation as well as increased proline content and activation of antioxidant enzymatic system.

European mammal exposure to lead from ammunition and fishing weight sources

Ammunition and fishing weight usage is the greatest largely unregulated contributor of lead (Pb) deposition to the European environment. While the range of negative impacts of Pb exposure to humans and avian wildlife are relatively well documented, little is known about risks to wild mammals despite recent scientific interest and publications. A qualitative risk assessment of the potential Source-Pathway-Receptor linkages for European mammal exposure was conducted, based on literature reviews and existing evidence and discussions with experts from the fields of wild mammal feeding ecology, behaviour and health.

The assessment identified 11 pathways for mammal exposure to Pb, with all 243 European species likely to be potentially exposed via one or more of these. All species were identified as potentially exposed via ingestion of water with elevated Pb from degraded ammunition/fishing weights. Ingestion of vegetation with elevated Pb from degraded ammunition/fishing weights potentially exposed many species (158), 78% of which had a potentially high risk of exposure when feeding in areas of high Pb deposition. Ingestion of retained ammunition in previously shot prey and/or discarded kill/gut piles with embedded ammunition was another significant pathway, contributing to predatory and scavenging carnivorous mammal exposure where an individual exposure event would be expected to be high.

The mechanisms by which Pb from ammunition and fishing weight sources are moved up trophic levels and ‘transferred’ from areas of high deposition into wider food chains e.g. via water, flying invertebrates and herbivores being subsequently preyed upon requires further investigation.

In conclusion, there are multiple and diverse Source-Pathway-Receptors linkages for European mammal exposures to Pb and evidence of exposure, from Europe and elsewhere, exists for some herbivores, carnivores, omnivores and insectivores. Both fatal but more likely non-fatal chronic and acute exposures may be expected to occur in wild European mammalian species, including those in poor conservation status.

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.

Genetic diversity and growth responses of Indonesian tomato (

Tomato (Solanum lycopersicum L.) is cultivated and consumed worldwide, including in Indonesia. It is used in the food, cosmetic, and pharmaceutical industries, due to its high content of carotenoid (lycopene) compounds that have antioxidant and anticancer activities. In Indonesia, although several cultivars of tomato are cultivated, including Opal, Permata, Mutiara, and Rewako, studies on their genetic information are limited. Unpredicted climate change as well as heavy metal contamination, especially Pb pollution, has threatened Indonesian food security. Therefore, our study aimed to analyze the genetic diversity of the four local tomatoes using random amplified polymorphic DNA (RAPD) markers and to determine the growth responses of several local tomato genotypes under Pb stress. In this study, morphological responses to Pb, including plant height and root length were observed. The RAPD analysis showed that Rewako and Permata were distinct, whereas Opal and Mutiara were closely related, possessing 81.8% similarity. Pb stress influenced plant height and root length in the four tomato genotypes, with each genotype exhibiting different morphological responses than others. However, the closely related Mutiara and Opal genotypes demonstrated similar responses to Pb stress to Permata and Rewako. Our study demonstrates that RAPD are sensitive and efficient for elucidating the genomic profile of the tomato genotypes. In addition, our results suggest that genetic variation among tomato genotypes might influence the morphological responses against Pb stress.

Zinc fortification and alleviation of cadmium stress by application of lysine chelated zinc on different varieties of wheat and rice in cadmium stressed soil

Sustainable and cost-effective methods are required to increase the food production and decrease the toxic effects of heavy metals. Most of the agriculture land is contaminated with cadmium (Cd). The present study was designed to minimize the toxic effect of Cd stress (0, 10 and 20 mg kg1-) on tolerant and sensitive varieties of wheat (Punjab-2011; Sammar) and rice (Kisan Basmati; Chenab) under Zn-lysine (Zn-lys) application as foliar spray (0, 12.5 and 25 mM) and seed priming (0, 3 and 6 ppm). Remarkable decrease was observed in plant growth, physiology and biochemistry as well as increase in Cd uptake, roots to shoots and grains of both crops. Cd significantly reduced the root and shoot lengths, root and shoot dry weights, transpiration rate, photosynthetic rate, stomatal conductance and water use efficiency as well as chlorophyll contents associated with enhanced electrolyte leakage (EL), malondialdehyde (MDA) and H2O2 and Cd uptake in different plant parts including grains of both crop varieties. The foliar application of Zn-lys (0, 12.5 and 25 mM) ameliorated the toxic effect of Cd on growth and physiology associated with decrease in EL, MDA and H2O2 and improved the activities of SOD, POD, CAT and APX enzymes with decreasing Cd uptake in tolerant varieties of wheat and rice as compared to seed priming. Furthermore, it has been investigated that the foliar application of Zn-lys is effective to improve quality of wheat and rice tolerant varieties (Punjab-2011 and Chenab) under Cd contamination soils.

Growth tolerance, concentration, and uptake of heavy metals as ameliorated by silicon application in vegetables

Lead (Pb) and cadmium (Cd) are among the heavy metals with phytotoxic and toxic effects on vegetables resulting in a significant decrease in crop yields. On the contrary, silicon (Si) has beneficial effects in enhancing plants' tolerance to biotic and abiotic stresses such as that imposed by heavy metals. This study evaluated the effects of Pb and Cd on the growth, biomass, and ameliorative mechanism of Si on concentration and uptake by leafy vegetables: spinach, kale, and amaranth. The greenhouse experiment treatments were Pb, Pb + Si, Cd, Cd + Si, Si, and control. These were arranged as a split-plot in a complete randomized design (CRD): main plots constituted vegetable species and treatments as subplots. The field experiment was carried in the Kenyatta University Research Farm, and treatments included Si application and control, arranged in a randomized complete block design (RCBD). Cadmium application reduced root biomass by 53-70% while Pb reduced it by 54-61% when compared with control. Silicon fertilization enhanced biomass tolerance by three-folds' and significantly (p < 0.001) reduced concentration and uptake of Pb and Cd. Results indicated a strong negative correlation between Cd concentrations and growth parameters (r = 0.8). The study recommends Si application to enhance leafy vegetables' tolerance to Pb and Cd.

The role of roots and rhizosphere in providing tolerance to toxic metals and metalloids

Human activity and natural processes have led to the widespread dissemination of metals and metalloids, many of which are toxic and have a negative impact on plant growth and development. Roots, as the first point of contact, are essential in endowing plants with tolerance to excess metal(loid) in the soil. The most important root processes that contribute to tolerance are: adaptation of transport processes that affect uptake efflux and long-distance transport of metal(loid)s; metal(loid) detoxification within root cells via conjugation to thiol rich compounds and subsequent sequestration in the vacuole; plasticity in root architecture; the presence of bacteria and fungi in the rhizosphere that impact on metal(loid) bioavailability; the role of root exudates. In this review, we provide details on these processes and assess their relevance on the detoxification of arsenic, cadmium, mercury and zinc in crops. Furthermore, we assess which of these strategies have been tested in field conditions and whether they are effective in terms of improving crop metal(loid) tolerance.

Metal Accumulation and Biomass Production in Young Afforestations Established on Soil Contaminated by Heavy Metals

The restoration of forest ecosystems on metal-contaminated sites can be achieved whilst producing valuable plant biomass. Here, we investigated the metal accumulation and biomass production of young afforestations on contaminated plots by simulating brownfield site conditions. On 16 3-m² plots, the 15 cm topsoil was experimentally contaminated with Zn/Cu/Pb/Cd = 2854/588/103/9.2 mg kg⁻¹ using smelter filter dust, while 16 uncontaminated plots (Zn/Cu/Pb/Cd = 97/28/37/< 1) were used as controls. Both the calcareous (pH 7.4) and acidic (pH 4.2) subsoils remained uncontaminated. The afforestations consisted of groups of conifers, deciduous trees, and understorey plants. During the four years of cultivation, 2254/86/0.35/10 mg m⁻² Zn/Cu/Pb/Cd were extracted from the contaminated soils and transferred to the aboveground parts of the plants (1279/72/0.06/5.5 mg m⁻² in the controls). These extractions represented 3/2/3% of the soluble soil Zn/Cu/Cd fractions. The conifers showed 4–8 times lower root-to-shoot translocation of Cu and Zn than the deciduous trees. The contamination did not affect the biomass of the understorey plants and reduced that of the trees by 23% at most. Hence, we conclude that the afforestation of brown field sites with local tree species is an interesting option for their reclamation from an ecological as well as economic perspective.

Melatonin Protects Tobacco Suspension Cells against Pb-Induced Mitochondrial Dysfunction

Recent studies have shown that melatonin is an important molecule in plant physiology. It seems that the most important is that melatonin effectively eliminates oxidative stress (direct and indirect antioxidant) and switches on different defence strategies (preventive and interventive actions) during environmental stresses. In the presented report, exogenous melatonin potential to protect Nicotiana tabacum L. line Bright Yellow 2 (BY-2) exposed to lead against death was examined. Analyses of cell proliferation and viability, the level of intracellular calcium, changes in mitochondrial membrane potential (ΔΨm) as well as possible translocation of cytochrome c from mitochondria to cytosol and subsequent caspase-like proteolytic activity were conducted. Our results indicate that pretreatment BY-2 with melatonin protected tobacco cells against mitochondrial dysfunction and caspase-like activation caused by lead. The findings suggest the possible role of this indoleamine in the molecular mechanism of mitochondria, safeguarding against potential collapse and cytochrome c release. Thus, it seems that applied melatonin acted as an effective factor, promoting survival and increasing plant tolerance to lead.

Genotoxicity and Cytotoxicity Induced in Zygophyllum fabago by Low Pb Doses Depends on the Population’s Redox Plasticity

Lead (Pb) soil contamination remains a major ecological challenge. Zygophyllum fabago is a candidate for the Pb phytostabilisation of mining tailings; nevertheless, the cytogenotoxic effects of low doses of Pb on this species are still unknown. Therefore, Z. fabago seeds collected from non-mining (NM) and mining (M) areas were exposed to 0, 5 and 20 µM Pb for four weeks, after which seedling growth, Pb cytogenotoxic effects and redox status were analyzed. The data revealed that Pb did not affect seedling growth in M populations, in contrast to the NM population. Cell cycle progression delay/arrest was detected in both NM and M seedlings, mostly in the roots. DNA damage (DNAd) was induced by Pb, particularly in NM seedlings. In contrast, M populations, which showed a higher Pb content, exhibited lower levels of DNAd and protein oxidation, together with higher levels of antioxidants. Upon Pb exposure, reduced glutathione (GSH) and non-protein thiols were upregulated in shoots and were unaffected/decreased in roots from the NM population, whereas M populations maintained higher levels of flavanols and hydroxycinnamic acids in shoots and triggered GSH in roots and shoots. These differential organ-specific mechanisms seem to be a competitive strategy that allows M populations to overcome Pb toxicity, contrarily to NM, thus stressing the importance of seed provenance in phytostabilisation programs.

Critical Review of Lead Pollution in Bangladesh

BACKGROUND

Lead (Pb) poses a severe threat to human health and the environment. Worldwide Pb production and consumption have significantly increased along with unplanned industrialization and urbanization, lead smelting, and lead-acid battery processing. The improper management of Pb-containing elements is responsible for Pb pollution. Lead's persistence in nature and bioaccumulation in the food chain can lead to adverse health impacts.

OBJECTIVES

The present study aims to describe Pb contaminated sites in Bangladesh and Pb concentration in the atmosphere, water, sediments, soil, vegetables, fish, and other foods in Bangladesh.

METHODS

The present study searched a total of 128 peer-reviewed articles based on a predefined set of criteria (keywords, peer-reviewed journals, and indexing in Scopus, Science Direct, Web of Science, Springer, PubMed, Directory of Open Access Journals (DOAJ), and Bangladesh Journals Online (BanglaJOL) and exclusion criteria (predatory journal and absence of full text in English) and finally selected 63 articles (58 research articles and five (5) reports). The relevant findings on Pb exposure, sources, routes, diet, and impacts in Bangladesh were combined and presented.

RESULTS

The reviewed studies identified 175 Pb contaminated sites through soil sample assessment in Bangladesh. The study determined Pb concentrations in air (0.09-376.58 μg/m3, mean 21.31 μg/m3), river water (0.0009-18.7 mg/l, mean 1.07 mg/l), river sediments (4.9-69.75 mg/kg, mean 32.08 mg/kg), fish (0.018-30.8 mg/kg, mean 5.01 mg/kg), soil (7.3-445 mg/kg, mean 90.34 mg/kg), vegetables (0.2-22.09 mg/kg, mean 4.33 mg/kg) and diet items (0.001-413.9 mg/kg, mean 43.22 mg/kg) of which 38.8%, 27.8%, 54.5%, 68.8%, 9.7% and 100% of samples, respectively, exceeded related World Health Organization (WHO), Food and Agriculture Organization (FAO), United States Environmental Protection Agency (USEPA) and Bangladesh Standard Testing Institution (BSTI) guidelines. The present study found that industrial soils are severely polluted with Pb (7.3-445 mg/kg) in Bangladesh. A high Pb concentration has been found in fish muscle and foods, including leafy and non-leafy vegetables collected from different places in Bangladesh.

CONCLUSIONS

Lead-contaminated foods can enter the human body through dietary intake and consequently lead to long-term adverse health effects. This study may help policymakers to formulate national policies with effective mitigation plans to combat the adverse health impacts of Pb in Bangladesh.

COMPETING INTERESTS

The authors declare no competing financial interests.

The Salicornia europaea potential for phytoremediation of heavy metals in the soils under different times of wastewater irrigation in northwestern Iran

The use of wastewater for irrigation usually leads to the buildup of potentially toxic elements (PTEs) in soils. The objective of this study was to assess the capacity of Salicornia europaea L. to uptake heavy metal when irrigated with wastewater at the vegetative, flowering, and reproductive stages of S. europaea for 2 and 4 days (in each stage) in the coastal saline area of Lake Urmia. The concentrations of heavy metals were detected in irrigated water, soil, and plant samples, while transfer factor (TF), bioconcentration factor (BCF), and bioaccumulation factor (BAF) were calculated. The results revealed that metal concentrations in the wastewater were above the permissible limits. The wastewater irrigation caused higher shoot biomass despite the high uptake of PTEs. Levels of Fe and Cu in plants were higher when irrigated with wastewater at the reproductive stage as compared to flowering and vegetative stages. The TF of wastewater-irrigated plants was higher at the flowering stage. TF of different metals at the flowering stage were in order of Zn > Pb > Ni > Cd > Cu, while the BCF increased in the order Cd > Cu > Zn > Ni > Pb. The BAF of the investigated PTEs at the flowering stage increased in the order Cd > Pb > Ni > Zn > Cu. In conclusion, higher Pb and Zn in the shoot indicated that the plant exhibited the phytoextraction mechanism, while Salicornia used a phytostabilization mechanism for roots-Cu, Ni, and Cd.

Exogenous 24-Epibrassinolide stimulates root protection, and leaf antioxidant enzymes in lead stressed rice plants: Central roles to minimize Pb content and oxidative stress

Lead (Pb) is an environmental pollutant that negatively affects rice plants, causing damage to the root system and chloroplast structures, as well as reducing growth. 24-Epibrasnolide (EBR) is a plant growth regulator with a high capacity to modulate antioxidant metabolism. The objective of this research was to investigate whether exogenous EBR application can mitigate oxidative damage in Pb-stressed rice plants, measure anatomical structures and evaluate physiological and biochemical responses connected with redox metabolism. The experiment was randomized with four treatments, including two lead treatments (0 and 200 μM PbCl₂, described as - Pb and + Pb, respectively) and two treatments with brassinosteroid (0 and 100 nM EBR, described as - EBR and + EBR, respectively). The results revealed that plants exposed to Pb suffered significant disturbances, but the EBR alleviated the negative interferences, as confirmed by the improvements in the root structures and antioxidant system. This steroid stimulated the root structures, increasing the epidermis thickness (26%) and aerenchyma area (50%), resulting in higher protection of this tissue against Pb²⁺ ions. Additionally, EBR promoted significant increases in superoxide dismutase (26%), catalase (24%), ascorbate peroxidase (54%) and peroxidase (63%) enzymes, reducing oxidative stress on the photosynthetic machinery in Pb-stressed plants. This research proved that EBR mitigates the toxic effects generated by Pb in rice plants.

Menadione sodium bisulfite alleviated chromium effects on wheat by regulating oxidative defense, chromium speciation, and ion homeostasis

Menadione sodium bisulfite (MSB) is a crucial growth regulator mediating plant defense response. MSB-mediated regulation of defense mechanisms in wheat under chromium (Cr) toxicity has not been reported in the literature. Therefore, the present study was undertaken to appraise the efficacy of exogenous MSB on circumventing Cr phytotoxic effects on wheat. We also compared the effects of water-soluble MSB with that of water-insoluble menadiol diacetate (MD). The levels used in the present investigation for MSB and MD were 100 and 200 mg L-1. Wheat plants grown in soil contaminated with 25 mg kg-1 Cr in the form of K2Cr2O7 showed a notable reduction in growth, chlorophyll molecules, relative water contents, grain yield, total soluble sugars, phenolics, flavonoids, ascorbic acid, activities of antioxidant enzymes (SOD, POD, CAT), and uptake of essential nutrients (K, P, and Ca). Cr toxicity caused a noticeable accretion in total free amino acids, proline, malondialdehyde, H2O2, O2•-, relative membrane permeability, methylglyoxal contents, activities of enzymes (lipoxygenase, glutathione-S-transferase, and ascorbate peroxidase), nitric oxide and H2S contents, glutathione and oxidized glutathione contents, total Cr contents, and Cr6+ and Cr3+ accumulation. MSB application significantly reduced lipid peroxidation, ROS overproduction, methylglyoxal levels, total Cr contents, and maintained higher Cr3+:Cr6+ ratio in aerial parts. Besides, Cr-mediated inhibition in essential nutrient uptake was significantly circumvented by exogenous MSB. Consequently, MSB enhanced wheat growth by lessening oxidative damage, total Cr contents in aerial parts, and strengthening antioxidant enzyme activities. MD was not effective in mediating defense responses in wheat under Cr toxicity.

Insights into the Interactions among Roots, Rhizosphere, and Rhizobacteria for Improving Plant Growth and Tolerance to Abiotic Stresses: A Review

Abiotic stresses, such as drought, salinity, heavy metals, variations in temperature, and ultraviolet (UV) radiation, are antagonistic to plant growth and development, resulting in an overall decrease in plant yield. These stresses have direct effects on the rhizosphere, thus severely affect the root growth, and thereby affecting the overall plant growth, health, and productivity. However, the growth-promoting rhizobacteria that colonize the rhizosphere/endorhizosphere protect the roots from the adverse effects of abiotic stress and facilitate plant growth by various direct and indirect mechanisms. In the rhizosphere, plants are constantly interacting with thousands of these microorganisms, yet it is not very clear when and how these complex root, rhizosphere, and rhizobacteria interactions occur under abiotic stresses. Therefore, the present review attempts to focus on root–rhizosphere and rhizobacterial interactions under stresses, how roots respond to these interactions, and the role of rhizobacteria under these stresses. Further, the review focuses on the underlying mechanisms employed by rhizobacteria for improving root architecture and plant tolerance to abiotic stresses.

Assessment of lead tolerance on Glycine max (L.) Merr. at early growth stages

Lead (Pb) contamination of agricultural soils, and subsequently of crops, has been widely reported. Soybean (Glycine max (L.) Merr.) has been indicated as a plant that accumulates Pb, even in soils that do not exceed the maximum permissible levels. Considering the toxicity of this heavy metal, the aim of the present study was to assess different concentrations of Pb, from low to extremely high (0.25 mM, 1 mM, and 2.5 mM), in soybean seedlings and their tolerance by analyzing morpho-physiological parameters in hydroponic experiments. Soybean seedlings were exposed to control and Pb treatments during 8 days, coinciding with the early growth stages, and the following variables were analyzed: biomass, Pb content in roots, stems and leaves, photosynthetic efficiency, leaf area, biochemical response (antioxidant power, chlorophylls, malondialdehyde), and relative water content of leaves. Results showed that roots accumulated much more Pb than the other organs, with Pb accumulation in roots being saturated even at the lowest Pb concentration, which was reflected in root biomass. Moreover, absorption of culture solutions was lower in Pb treatments, which was also reflected in the lower leaf relative water content. Lead toxicity symptoms in leaves (chlorosis and dark spots, and a decrease of biomass and leaf area, chlorophyll content, and photosynthetic efficiency), and an increase of the oxidative defense system were associated only with the highest Pb concentration (2.5 mM). Our findings support the evidence of soybean as a species tolerant to Pb, showing the effects of toxicity at very high concentrations.

Pb Stress and Ectomycorrhizas: Strong Protective Proteomic Responses in Poplar Roots Inoculated with Paxillus involutus Isolate and Characterized by Low Root Colonization Intensity

The commonly observed increased heavy metal tolerance of ectomycorrhized plants is usually linked with the protective role of the fungal hyphae covering colonized plant root tips. However, the molecular tolerance mechanisms in heavy metal stressed low-colonized ectormyocrrhizal plants characterized by an ectomycorrhiza-triggered increases in growth are unknown. Here, we examined Populus × canescens microcuttings inoculated with the Paxillus involutus isolate, which triggered an increase in poplar growth despite successful colonization of only 1.9% ± 0.8 of root tips. The analyzed plants, lacking a mantle—a protective fungal biofilter—were grown for 6 weeks in agar medium enriched with 0.75 mM Pb(NO₃)₂. In minimally colonized ‘bare’ roots, the proteome response to Pb was similar to that in noninoculated plants (e.g., higher abundances of PM- and V-type H⁺ ATPases and lower abundance of ribosomal proteins). However, the more intensive activation of molecular processes leading to Pb sequestration or redirection of the root metabolic flux into amino acid and Pb chelate (phenolics and citrate) biosynthesis coexisted with lower Pb uptake compared to that in controls. The molecular Pb response of inoculated roots was more intense and effective than that of noninoculated roots in poplars.

Targeting aquaporins to alleviate hazardous metal(loid)s imposed stress in plants

Uptake of hazardous metal(loid)s adversely affects plants and imposes a threat to the entire food chain. Here, the role of aquaporins (AQPs) providing tolerance against hazardous metal(loid)s in plants is discussed to provide a perspective on the present understanding, knowledge gaps, and opportunities. Plants adopt complex molecular and physiological mechanisms for better tolerance, adaptability, and survival under metal(loid)s stress. Water conservation in plants is one such primary strategies regulated by AQPs, a family of channel-forming proteins facilitating the transport of water and many other solutes. The strategy is more evident with reports suggesting differential expression of AQPs adopted by plants to cope with the heavy metal stress. In this regard, numerous studies showing enhanced tolerance against hazardous elements in plants due to AQPs activity are discussed. Consequently, present understanding of various aspects of AQPs, such as tertiary-structure, transport activity, solute-specificity, differential expression, gating mechanism, and subcellular localization, are reviewed. Similarly, various tools and techniques are discussed in detail aiming at efficient utilization of resources and knowledge to combat metal(loid)s stress. The scope of AQP transgenesis focusing on heavy metal stresses is also highlighted. The information provided here will be helpful to design efficient strategies for the development of metal(loid)s stress-tolerant crops.

Lead uptake and translocation pathways in soybean seedlings: the role of ion competition and transpiration rates

Glycine max (L.) Merr. (soybean) crop plants have been found to have high lead (Pb) levels in aerial organs; however, knowledge about the processes involved in the incorporation, and subsequent translocation and accumulation of the metal in the plants is scarce. Considering the toxicity of this heavy metal, the aim of the present study was to evaluate Pb uptake and translocation, and their toxic effects on soybean seedlings via experiments of ionic competition with Ca2+ (2.5 mM, Ca:Pb 1:1) and alteration of the transpiration flow [0.25 mM Pb(NO3)2]. The following variables were analyzed: biomass, leaf area (morphological parameters), photosynthetic efficiency, biochemical response (considered physiological stress markers: antioxidant power, chlorophylls, carotenoids, starch, proteins, sugars, and malondialdehyde), and Pb content. Results showed that soybean seedlings can accumulate high Pb concentration in its organs; however, in general, no morpho-physiological Pb stress symptoms were observed, except for lipid peroxidation and antioxidant power. The treatment with Ca ions was not effective in reducing Pb entry into root over time when both Ca and Pb where present in the grow solution. Alteration of the transpiration rate in soybean showed that the air flow increased the consumption of solutions, regardless of the treatments. However, Pb accumulation was lower in seedlings exposed to air flow, indicating a selective exclusion of the metal in the solution. In both experiments, soybean seedlings showed to be tolerant to high Pb concentrations.