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

Biomarkers of heavy metals pollution in mangrove ecosystems: Comparative assessment in industrial impact and conservation zones

Heavy metal contamination from industrial activities in coastal regions can lead to pollution in mangrove ecosystems. Mangroves produce antioxidant compounds to mitigate the impact of free radicals. This study aimed to analyze the correlation between the concentration of heavy metals Pb and Cu and antioxidant activity in Avicennia alba and Excoecaria agallocha mangroves from areas affected by industrial activities and conservation areas, Banyuasin, South Sumatra, Indonesia. This study was conducted in September 2023 with sampling locations in the Payung Island area and the Barong River conservation area, Berbak Sembilang National Park. The samples taken included sediment and mangrove leaves. The concentration of heavy metals Pb and Cu was measured by atomic absorption spectrometry. Antioxidant activity test using the DPPH test, total phenol using the Folin-Ciocalteu method, and phytochemical profile screening using GCMS. Statistical analysis of the correlation between antioxidant activity and heavy metal concentration using the Pearson correlation. The results showed that the highest concentration of heavy metals in sediment and mangrove leaves was found in the area affected by industrial activity, with a range of Pb values of 0.67 ± 0.16-18.70 ± 0.48 mg/kg and Cu values of 3.39 ± 0.20-6.07 ± 0.37 mg / kg. The results of sediment pollution assessment for heavy metals Pb and Cu at Igeo < 0 indicates uncontaminated, 1 < Cf < 3 indicates low contamination, and PLI 0-2 indicates not polluted. While the results of heavy metal bioaccumulation in leaves were BCF < 1, indicates low bioaccumulation. E. agallocha leaves from the Pulau Payung area showed very strong antioxidant activity of 21.63 μg/ml, and the highest total phenol content reached 398.80 mg GAE/g. Analysis of compounds with the highest antioxidant activity identified the presence of esters, aldehydes, alcohols, fatty acids, glycosides, flavonoids, terpenoids, and steroids. Correlation analysis shows that higher heavy metal concentrations correspond to increased antioxidant activity and total phenol content (r ≠ 0). These findings are expected to contribute to scientific knowledge that enhances environmental sustainability, supporting effective management of coastal natural resources.

Foliar Spray of Cerium Oxide Nanoparticles (CeO2 NPs) Improves Lead (Pb) Resistance in Rice

The widespread use of lead (Pb) has led to serious environmental and human health problems worldwide. The application of oxide nanoparticles (CeO2 NPs) in alleviating abiotic stress in plants has received extensive attention. In this study, 50 mg·L-1 CeO2 NPs can improve Pb resistance and promote rice growth. Specifically, this study observed that CeO2 NPs increased the activity of antioxidant enzymes peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), but the difference did not reach a significant level. At the same time, CeO2 NPs upregulated antioxidant metabolites alpha-linolenic acid, linoleic acid, ferulic acid, and kaempferol under Pb stress. In addition, CeO2 NPs upregulated multiple defense response-related genes, such as OsOPR1 and OsPR10a; RPR10a, and improved rice carbon flow and energy supply by upregulating sucrose and D-glucose. The results of this study provided technical support for alleviating Pb stress in rice.

Metabolomic evaluation of selenium seed priming on mitigating lead stress toxicity in Vicia faba plants

BACKGROUND

Persistent lead contamination and the absence of natural remediation elements exacerbate the long-term toxicity of plants. Nevertheless, it has been consistently shown that selenium has a protective effect against heavy metal toxicity in plants. Consequently, it is imperative to identify the metabolic pathways that selenium employs to enhance the resistance of plants to lead stress. This study aimed to investigate the metabolomic alterations induced by selenium priming of Vicia faba seeds to enhance their tolerance to lead stress.

RESULTS

Selenium seed priming significantly improved the growth parameter and mitigated the adverse growth consequences observed under lead stress. Nuclear magnetic resonance-based metabolomic analysis identified 58 metabolites in the polar extracts of the shoots, with the metabolites composed of amino acids (40%), carboxylic acids (12%), fatty acids (11%), carbohydrates (5%), alkaloids (5%), and phenols (4%). The addition of Pb facilitated the biosynthesis of unique metabolites, including 2-methylglutarate, 3-methyladipate, and epinephrine, which were absent in control and selenium-treated samples. Conversely, 4-aminobutyrate and 2-methylglutarate were entirely absent in Pb samples. Selenium-treated plants accumulated trigonelline and AMP at levels 1.4 and 6.0 times, respectively, more than the control samples. Selenium-primed plants exposed to lead stress exhibited higher levels of asparagine, tryptophan, and xanthine compared to other treatments. As determined by both enrichment analysis and pathway analysis, the most significantly altered pathways were alanine, aspartate, and glutamate metabolism; aminoacyl-tRNA biosynthesis; and valine, leucine, and isoleucine biosynthesis pathways.

CONCLUSION

The results demonstrate the crucial role of selenium priming in enhancing the growth and lead stress resistance of Vicia faba plants by significantly altering the concentrations of key metabolites and metabolic pathways, particularly those involved in amino acid metabolism, offering a promising strategy for improving plant resilience to heavy metal contamination.

Phytoremediation of Lead-Contaminated Soils Using Indian Mustard: Influence of Organic and Inorganic Amendments

Lead (Pb) contamination in the environment poses significant risks to ecosystems and human health. Effective management strategies are crucial for mitigating its impact. This study investigated the immobilization and bioavailability of Pb in soils, amended with press-mud, farmyard manure (FYM), lime and silt + clay, with Indian mustard (Brassica juncea L.). Loamy sand soil was spiked with lead nitrate at concentrations of 0, 50, 100, 200 and 400 mg kg- 1 Pb. Indian mustard (RLM 619) was raised in treated microcosms upto maturity with adequate application of NPK fertilizers. The total mean dry matter yield of Indian mustard harvested at maturity decreased with increasing Pb levels. At all Pb levels, the application of different amendments, except lime, increased micronutrient content. Addition of amendments generally enhanced the nutrient content in seeds. We concluded that the silt + clay amendment was the most effective in reducing Pb bioavailability to Indian mustard. Future research should explore the long-term effects of amendments on the sustainability of Pb immobilization across various soil types. Additionally, assessing Indian mustard for large-scale remediation will provide valuable insights for developing more effective and eco-friendly management strategies.

Mitigating effect of γ-aminobutyric acid and gibberellic acid on tomato plant cultivated in Pb-polluted soil

Soil heavy metal pollution poses a significant environmental risk to human health and plant growth. Gibberellic acid (GA) and γ-aminobutyric acid (GABA) are effective methods for resolving this issue. GA regulates growth mechanisms such as seed germination, flowering, and stem elongation. Plants use GABA, a signaling molecule, to control physiological processes, growth, and responses to stress. This substance plays a crucial role in the interactions between hormones and plant defense, as evidenced by its effects on photosynthesis, food absorption, and stomatal behavior. The study aimed to determine how GABA and GA amendments affected tomato plants under no toxicity and Pb toxicity. The study included four treatments (0, GA, GABA, and GA + GABA) in four replications following a completely randomized design. Notably, the GA + GABA treatment led to considerable enhancements in fresh weight (88.98%), dry weight (68.28%), shoot length (39.98%), and root length (115.43%) compared to the control under Pb toxicity. Moreover, GA + GABA treatment significantly increased tomato chlorophyll a (161.72%), chlorophyll b (93.33%), and total chlorophyll content (112.45%) under Pb stress toxicity, confirming the effectiveness of GA + GABA treatment. In conclusion, GA + GABA is recommended as the best amendment to mitigate Pb stress in tomato plants. Our findings have broader implications for GA + GABA application, offering a potential technology to enhance sustainable crop production by improving plant growth and yield in Pb-contaminated soils. More investigations are suggested at field levels under different agroclimates on different crops for the declaration of GA + GABA as the best amendment for alleviating different heavy metal pollutions and sustainable agriculture productions.

Factors influencing heavy metal contamination in black pepper fields: a randomized study of the traditional chemical fertilized black pepper fields of South India concerning soil types

Despite the prevalence of heavy metal contamination in crop fields, targeted studies examining how factors like soil type affect contamination in chemically fertilized fields are scarce. This study assessed heavy metal contamination in Kerala's traditional black pepper fields, focusing on soil types-both soil order and series-and cultivation practices. We collected 266 soil samples from 70 diverse black pepper fields across five districts, which were categorized into 39 composite samples representing 13 soil series from two soil orders based on standard previous studies. Using Inductively Coupled Plasma-Mass Spectrometry, we quantitatively measured nine heavy metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) along with macronutrients (Mg and Ca). We analyzed heavy metal indices, including contamination factor, geo-accumulation index, pollution load index (PLI), and human health risk assessment, and explored correlations between heavy metals and soil nutrient parameters. It indicated that Cd, Zn, Cr, Pb, and Cu were the contaminants in the region's black pepper soils, while Fe and Mn levels were within natural limits. The PLI > 1 indicated significant contamination across both soil orders and most soil series. Mg levels were significantly higher (p > 0.05) in chemicalized fields, but Ca was undetectable in most samples, except from the Paippara series. Notable correlations were found between heavy metals and soil fertility parameters. This study underscores the extent of heavy metal contamination in black pepper fields relative to soil types and emphasizes the need for tailored soil fertility amendments and pesticide applications to promote sustainable agricultural practices.

Environmental Contamination and Mining Impact: Physico-Chemical and Biological Characterization of Propolis as an Indicator of Pollution in the Roșia Montană Area, Romania

Contamination with heavy metal ions from mining activities presents a major environmental issue. This study investigates pollution caused by heavy metals from mining, with a particular emphasis on toxic ions and essential ions for living organisms. It starts by analyzing the sources of pollution and its effects on soil, vegetation, water, and wildlife (propolis produced by honey bees living in natural environments). Propolis is an indicator of environmental contamination by metals, a natural and valuable product of natural ecosystems. As part of the investigation, the contamination with metal cations (Pb2+, Cu2+, Cd2+, Zn2+, As3+, Fe2+, and Sr2+) of the soil, cultivated vegetables (carrot, turnip, onion, potato) was monitored in 9 points in the Roșia Montană area, Romania, as well as the river that runs through the area. The maximum values of the parameters investigated were recorded in soil (108.32 mg/kg Pb2+, 23.06 mg/kg Cd2+, 102.17 mg/kg As3+), river water (11.00 µg/L Pb2+, 903.47 µg/L Cu2+, 60.13 µg/L Cd2+, 1903.08 µg/L Zn2+, 148.07 µg/L As3+, 44,024.08 µg/L Fe2+), vegetables (0.72 mg/kg Pb2+, 0.17 mg/kg Cd2+) and it was followed whether the same heavy metals are found in propolis (maximum values 10.14 mg/kg Pb2+, 6.32 mg/kg Cu2+, 0.158 mg/kg Cd2+, 6.0 Zn2+, 1.04 mg/kg As3+, 12.06 mg/kg Sr2+). The parameters analyzed for the river waters were pH, sulfates, the oxygen and nutrient regime, and microbial load. Additional investigations were carried out into the quality of these propolis samples: water activity, moisture, hygroscopicity, water solubility, volatile oils, oxidation index, measuring point, density, dry matter, material insoluble in ethanol, extractable with ethanol, ash, and wax. The highest values were 189.4 mg GAE/g for phenols, 84.31 mg QE/g for flavonoids, and 0.086 µg/mL for IC50 antioxidant activity. This study indicates that bee products, such as propolis, can be an indicator of pollution in mining areas.

Exploring the phytoremediation potential of plant species in soils impacted by gold mining in Northern Colombia

Contamination of soils with toxic metals poses significant threats to human health and ecosystems. Plant-based remediation strategies can play a vital role in mitigating these risks, and the use of plants as a remediation strategy can help reduce these risks. In this study, we investigate the remediation potential of native plants in accumulating and translocating metal(loid)s at a Colombian site impacted by gold mining. The remediation capacity is evaluated using the translocation factor (TF) from roots to shoots and the bioconcentration factor (BCF) from soil to roots. Metal(loid) concentrations in the soil followed the order: Fe > As > Hg > Cd > Pb > Zn > Mn > Cu. In plant tissues, Hg showed higher accumulation in leaves (3.5 mg/kg) compared to roots (2.8 mg/kg). Pb (17.7 mg/kg), As (3.8 mg/kg), Fe (2.5 mg/kg) and Cd (1.2 mg/kg) concentracions were also higher in roots. Metal concentrations in the stems, were generally below 1.0 mg/kg, except for Pb (15.0 mg/kg) and Hg (1.0 mg/kg). The highest BCF values for Hg were observed in Spondias mombin L. (18.7), Cecropia peltata L. (8.3) and Gliricidia sepium (Jacq.) Walp (4.4). On the other hand, Senna alata (L.) Roxb., Psidium guajava L. and Morinda citrifolia L. exhibited notable BFC values for As with 44.7, 6.3 and 5.9, respectively. Musa x paradisiaca L. had the highest BCF for Cd (1.8). M. citrifolia (4.3) and Annona muricata L. (3.2) exhibited the highest TF for Hg, while Tabebuia rosea (Bertol.) Bertero ex A.DC. (4.9) and Paspalum fasciculatum Willd. ex (3.1) demonstrated elevated TF values for Pb. In conclusion, plants such as P. fasciculatum, A. muricata, M. citrifolia, G. sepium and T. rosea exhibit great potential for application in phytoremediation strategies in tropical regions impacted by gold mining activities.

Lead-induced changes in plant cell ultrastructure: an overview

Lead (Pb) is one of the most harmful toxic metals and causes severe damage to plants even at low concentrations. Pb inhibits plant development, reduces photosynthesis rates, and causes metabolic disfunctions. Plant cells display these alterations in the form of abnormal morphological modifications resulting from ultrastructural changes in the cell wall, plasma membrane, chloroplast, endoplasmic reticulum, mitochondria, and nuclei. Depending on plant tolerance capacity, the ultrastructural changes could be either a sign of toxicity that limits plant development or an adaptive strategy to cope with Pb stress. This paper gathers data on Pb-induced changes in cell ultrastructure observed in many tolerant and hyperaccumulator plants and describes the ultrastructural changes that appear to be mechanisms to alleviate Pb toxicity. The different modifications caused by Pb in cell organelles are summarized and reinforced with hypotheses that provide an overview of plant responses to Pb stress and explain the physiological and morphological changes that occur in tolerant plants. These ultrastructural modifications could help assess the potential of plants for use in phytoremediation.

Nanogel imprinting improving affinity and selectivity of domain-limited ssDNA aptamer to Pb2+: Interaction mechanisms revealed by molecular dynamics simulation

Aptamer conformations are susceptible to environmental conditions, which makes it difficult to achieve stable targets detection in complex environments with aptasensors. Imprinting strategy was proposed to immobilize the specific conformation of aptamers, aiming to enhance their recognition anti-interference. However, it is mechanistically unclear how the imprinted polymers affect aptamers' recognition, which limits application of the strategy. Herein, MD simulation was applied to explore the structural reason why nanogel imprinting improves binding affinity and selectivity of T30695 aptamer to Pb2+ observed experimentally. Results show the imprinted polymers stabilize the domain-limited T30695 by noncovalent interactions. The coating process undergoes three evolution stages, finally achieving a polymer-aptamer-polymer sandwich-shaped conformation. Notably, it was found the polymers provide additional non-specific binding of Pb2+ at acylamine group of acrylamide monomers, which accounts for the improved binding affinity with association constant Ka 2.5 times larger. More importantly, imprinting enhances selectivity of aptamer to Pb2+ by changing coordination mode of interfering ions (Ca2+, K+, Mg2+, NH4+ and Cu2+), which significantly destroys G-quadruplex conformation and thus its binding ability. This work revealed mechanistic effects of imprinting strategy on aptamers recognition at molecular level, which can guide rational design of high-performance aptamer-based biosensors applied in various detection areas.

Impact of rhizobacterial inoculation in plant growth medium to mitigate lead stress in Tomato (Solanum lycopersicum L.)

This study investigates the effects of lead stress on tomato plants and explores the potential role of plant growth-promoting rhizobacteria (PGPR) to alleviate this stress. The experiment was conducted in pots, introducing varying lead levels (0, 100, 200, 300, 400, and 500 mg kg⁻¹) using lead nitrate. For rhizobacterial inoculation, pre-characterized LTPGP strains S5 Pseudomonas fluorescens A506 and S10 Pseudomonas fluorescens LMG 2189 were used. Data were recorded on growth parameters (shoot and root length, fresh and dry weight), physiological attributes (chlorophyll content, proline content, electrolyte leakage, and lead accumulation), and antioxidant activities (catalase, peroxidase, superoxide dismutase) in tomato plants. Results revealed that lead contamination significantly impaired plant growth, reducing shoot and root lengths by approximately 49.78-57.62%, and negatively impacted physiological attributes and antioxidant enzyme activities. However, inoculation with PGPR strains S5 and S10 led to notable improvements in growth parameters, enhanced physiological traits, and better antioxidant activities, effectively mitigating lead stress. These findings highlights the potential of PGPR to improve tomato plant resilience to lead contamination.

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.

Assessing soil remediation effect of Cr and Pb based on bioavailability using DGT, BCR and standardized determination method

In the field of soil remediation, the importance of bioavailability of pollutants has not received adequate attention, leading to the excessive application of remediation measures. Therefore, to ensure the safe use of farmland soil, a scientific method is needed to assess labile contaminants and their translocation in plants. To evaluate soil remediation effect based on bioavailability, the concentrations of these heavy metals in soil were analyzed using by the method for total metal content, the Community Bureau of Reference (BCR) extraction, and the diffusive gradients in thin films (DGT) technique. The results reveal that the correlation coefficients between metal concentrations measured by DGT and those accumulated in rice grains are the highest (Cr-R2 = 0.8966, Pb-R2 = 0.9045). However, the capability of method for total metal content to evaluate the remediation effect of heavy metals is very limited. In contrast, although Cr and Pb measured by BCR show a high correlation with HMs in rice plants, the method still falls short in precisely assessing bioavailability. Significantly, DGT proves to be more effective, successfully distinguishing the remediation effects of different treatments. Generally, DGT offers a more accurate and simpler assessment method, underscoring its practical significance for monitoring soil remediation and environmental management.

Landfill leachate: An invisible threat to soil quality of temperate Himalayas

Landfills are the most affordable and popular method for managing waste in many parts of the world, However, in most developing nations, including India, the infiltration of hazardous materials from improperly managed dumping site continues to be a significant environmental problem. Around the world, leachate is a significant point source of contamination in numerous environmental media, including soil, groundwater, and surface water. Soil is an important asset as it is the key factor for food production and has tremendous significance in achieving sustainable development goals (SDGs). The contaminants from soil enter into food chain and ultimately reach humans. So in order to prevent the adverse effects of toxic elements on humans, there is need to maintain the soil quality and to prevent deterioration. Keeping in view the consequences of unscientific management of waste, the goal of the experiment was to determine how landfill leachate from Achan landfill affected the soil quality in the temperate Himalayas. All four seasons of the year, viz Spring, Summer, Autumn, and Winter, at four sites viz, Center of dumping site, inside, Outside and Control were monitored. Among sites center was found to have maximum value of EC (3.04 dS/m), Moisture content (42.51%), N (285.43 mg/kg), P (70.07 mg/kg), K (265.71 mg/kg), Ca (957.67 mg/kg), Mg(402.42 mg/kg), Zn (2.02 mg/kg), Fe (10.56 mg/kg), Cu (2.07 mg/kg), Mn (10.73 mg/kg), Pb (85.02 mg/kg), Cd (4.50 mg/kg), Ni (29.04 mg/kg), Cr (23.37 mg/kg), As (14.10 mg/kg). While as the lowest value of all parameters was reported at control site. From the study it is recommended that the waste generated is mostly organic (65-75%), thus can be segregated and treated at source. The waste can be treated at source using microbial consortium technology in order to transform the waste in to wealth in a sustainable way and to prevent the deterioration of soil quality.

Mitigating toxic metals contamination in foods: Bridging knowledge gaps for addressing food safety

Background

Reducing exposure to harmful substances in food is highly desired, especially for infants, young children, and pregnant women. A workshop focused on understanding and reducing toxic metal contamination in food was conducted involving leading scientists, educators, practitioners, and key stakeholders in conjunction with the USDA National Institute of Food and Agriculture.

Scope and approach

The goal of this review and the workshop was to advance the current knowledge of major toxic metals concerning food safety, viz. arsenic (As), lead (Pb), cadmium (Cd), mercury (Hg), and chromium (Cr), preventive measures, identify critical knowledge gaps, and the need for research, extension, and education. Being a part of the "Closer to Zero (C2Z)" initiative of the USDA, FDA, and other federal agencies, the workshop adopted a "One Health" approach to mitigate dietary exposure and environmental pollution of hazardous elements.

Key findings and conclusions

The experts discussed the accumulation of toxic metals in food crops and drinking water in relation to soil biogeochemistry, plant uptake, and multidisciplinary factors such as food processing, detection, regulatory standards, etc. To forward food safety, this workshop critically examined toxic metals contamination, exposure and toxicity along the farm-to-fork-to-human continuum, research gaps, prevailing regulations, and sustainable remediation approaches, and offered significant recommendations. This review paper provides perspective on key findings of the workshop relative to addressing this important aspect of food safety, emphasizing interdisciplinary research that can effectively investigate and understand the complex and dynamic relationships between soil biogeochemistry, the microbiome, plant tolerance and accumulation strategies, uniform standards for acceptable and safe toxic element levels in food and water, and raising public awareness. This article also provides a foundation for decision-making regarding toxic metal fate and effects, including risk management strategies, in the face of modern industrialization and a changing climate.

Exploiting the synergistic influence of AgNPs-TiO2NPs: enhancing phytostabilization of Pb and mitigating its toxicity in Vigna unguiculata

In this study, a composite of silver and titanium dioxide nanoparticles (AgNPs-TiO2NPs) was examined for its synergistic effects on phytostabilization of lead (Pb) and mitigation of toxicity in cowpea (Vigna unguiculata (L) Walp). Seeds of V. unguiculata were wetted with water, 0.05 and 0.1 mgL-1 Pb and 25 mgmL-1 each of AgNPs, TiO2NPs, and AgNPs-TiO2NPs. Root lengths of V. unguiculata were reduced by 25% and 44% at 0.05 and 0.1 mgL-1 Pb, respectively, while shoot lengths were reduced by 2% and 7%. In V. unguiculata, AgNPs and TiO2NPs significantly improved physiological indicators and mitigated Pb effects, with TiO2NPs modulating physiological parameters more effectively than AgNPs. The composite (AgNPs-TiO2NPs) synergistically regulated V. unguiculata physiology better than individual nanoparticles. Compared to individual AgNPs and TiO2NPs, the composite (AgNPs-TiO2NPs) synergistically increased antioxidant activity by 12% and 9%, and carotenoid contents by 88%. Additionally, AgNPs-TiO2NPs effectively reduced malondialdehyde levels by 29%, thereby mitigating the effects of Pb on V. unguiculata better than individual nanoparticles. AgNPs-TiO2NPs enhanced Pb immobilization by 57%, reducing its translocation from soil to shoots compared to V. unguiculata wetted with water. The bioconcentration and translocation factors of Pb indicate that phytostabilization was most effective when the composite was used.

A comparative study between the efficacy of fertigation and spraying procedures in terms of the content of Cadmium (Cd) and Arsenic (As) in greenhouse cucumber

A comparative study between fertigation and spraying procedures in terms of the status of Cadmium (Cd) and Arsenic (As) in greenhouse cucumber was conducted as a two-factor split plot based on a randomized complete block design with three replications at the Soil and Water Research Institute, Karaj, Iran in 2023. The main and sub-factors were respectively fertigation and spraying that were used in two levels [the maximum permissible concentration of Cd and As in granular triple super phosphate fertilizer (25 ppm Cd and 50 ppm As) and the minimum permissible concentration of these metals in granular triple super phosphate fertilizer (5 ppm Cd and 5 ppm As)]. Spraying was done in three modes (spraying of leaves, leaves and fruit, and fruit). On average, the results showed that the order of the concentration of Cd in plant tissues (DW) was as leaf (0.284 mg/kg) > fruit peel (0.102 mg/kg) > fruit peel + flesh (0.054 mg/kg) > fruit flesh (0.044 mg/kg). This order for As was as leaf (0.608 mg/kg) > fruit flesh (0.127 mg/kg) > fruit peel + flesh (0.109 mg/kg) > fruit peel (0.072 mg/kg). Based on the measurements, the spraying procedure accumulated more amounts of Cd and As in the fruit (i.e., peel + flesh) than the fertigation procedure. In general, it is concluded that under soilless culture, the status of heavy metals in plant tissues of greenhouse cucumber is related to the nature of the metal, the organ exposed to the metal, and the fertilization procedure. Because there is the risk of contamination of vegetables grown in the areas fertigated and sprayed with poor-quality nutrient solutions in terms of the content of heavy metals, the frequency of fertigation and spraying needs to be monitored continuously for the quality of the vegetables cultivated in greenhouses.

Plants' molecular behavior to heavy metals: from criticality to toxicity

The contamination of soil and water with high levels of heavy metals (HMs) has emerged as a significant obstacle to agricultural productivity and overall crop quality. Certain HMs, although serving as essential micronutrients, are required in smaller quantities for plant growth. However, when present in higher concentrations, they become very toxic. Several studies have shown that to balance out the harmful effects of HMs, complex systems are needed at the molecular, physiological, biochemical, cellular, tissue, and whole plant levels. This could lead to more crops being grown. Our review focused on HMs' resources, occurrences, and agricultural implications. This review will also look at how plants react to HMs and how they affect seed performance as well as the benefits that HMs provide for plants. Furthermore, the review examines HMs' transport genes in plants and their molecular, biochemical, and metabolic responses to HMs. We have also examined the obstacles and potential for HMs in plants and their management strategies.

Heavy metal stress and mitogen activated kinase transcription factors in plants: Exploring heavy metal-ROS influences on plant signalling pathways

Due to their stationary nature, plants are exposed to a diverse range of biotic and abiotic stresses, of which heavy metal (HM) stress poses one of the most detrimental abiotic stresses, targeting diverse plant processes. HMs instigate the overproduction of reactive oxygen species (ROS), and to mitigate the adverse effects of ROS, plants induce multiple defence mechanisms. Besides the negative implications of overproduction of ROS, these molecules play a multitude of signalling roles in plants, acting as a central player in the complex signalling network of cells. One of the ROS-associated signalling mechanisms is the mitogen-activated protein kinase (MAPK) cascade, a signalling pathway which transduces extracellular stimuli into intracellular responses. Plant MAPKs have been implicated in signalling involved in stress response, phytohormone regulation, and cell cycle cues. However, the influence of various HMs on MAPK activation has not been well documented. In this review, we address and summarise several aspects related to various HM-induced ROS signalling. Additionally, we touch on how these signals activate the MAPK cascade and the downstream transcription factors that influence plant responses to HMs. Moreover, we propose a workflow that could characterise genes associated with MAPKs and their roles during plant HM stress responses.

Flavonoid metabolism plays an important role in response to lead stress in maize at seedling stage

BACKGROUND

Pb stress, a toxic abiotic stress, critically affects maize production and food security. Although some progress has been made in understanding the damage caused by Pb stress and plant response strategies, the regulatory mechanisms and resistance genes involved in the response to lead stress in crops are largely unknown.

RESULTS

In this study, to uncover the response mechanism of maize to Pb stress phenotype, physiological and biochemical indexes, the transcriptome, and the metabolome under different concentrations of Pb stress were combined for comprehensive analysis. As a result, the development of seedlings and antioxidant system were significantly inhibited under Pb stress, especially under relatively high Pb concentrations. Transcriptome analysis revealed 3559 co-differentially expressed genes(co-DEG) under the four Pb concentration treatments (500 mg/L, 1000 mg/L, 2000 mg/L, and 3000 mg/L Pb(NO3)2), which were enriched mainly in the GO terms related to DNA-binding transcription factor activity, response to stress, response to reactive oxygen species, cell death, the plasma membrane and root epidermal cell differentiation. Metabolome analysis revealed 72 and 107 differentially expressed metabolites (DEMs) under T500 and T2000, respectively, and 36 co-DEMs. KEGG analysis of the DEMs and DEGs revealed a common metabolic pathway, namely, flavonoid biosynthesis. An association study between the flavonoid biosynthesis-related DEMs and DEGs revealed 20 genes associated with flavonoid-related metabolites, including 3 for genistin and 17 for calycosin.

CONCLUSION

In summary, the study reveals that flavonoid metabolism plays an important role in response to Pb stress in maize, which not only provides genetic resources for the genetic improvement of maize Pb tolerance in the future but also enriches the theoretical basis of the maize Pb stress response.