Pb Stress Research Articles

Impact of coconut-fiber biochar on lead translocation, accumulation, and detoxification mechanisms in a soil–rice system under elevated lead stress

Biochar, an environmentally friendly material, was found to passivate lead (Pb) in contaminated soil effectively. This study utilized spectroscopic investigations and partial least squares path modeling (PLS-PM) analysis to examine the impact of coconut-fiber biochar (CFB) on the translocation, accumulation, and detoxification mechanisms of Pb in soil-rice systems. The results demonstrated a significant decrease (p < 0.05) in bioavailable Pb concentration in paddy soils with CFB amendment, as well as reduced Pb concentrations in rice roots, shoots, and brown rice. Synchrotron-based micro X-ray fluorescence analyses revealed that CFB application inhibited the migration of Pb to the rhizospheric soil region, leading to reduced Pb uptake by rice roots. Additionally, the CFB treatment decreased Pb concentrations in the cellular protoplasm of both roots and shoots, and enhanced the activity of antioxidant enzymes in rice plants, improving their Pb stress tolerance. PLS-PM analyses quantified the effects of CFB on the accumulation and detoxification pathways of Pb in the soil–rice system. Understanding how biochar influences the immobilization and detoxification of Pb in soil–rice systems could provide valuable insights for strategically using biochar to address hazardous elements in complex agricultural settings.

Effects of Different Heavy Metal Stressors on the Endophytic Community Composition and Diversity of Symphytum officinale.

Endophytes play an important role in helping plants resist heavy metal stress. However, little is known about the effects of different heavy metals on the diversity and composition of endophyte communities. In this study, we used 16S and ITS amplicon sequencing to reveal the structure and function of endophytes in Symphytum officinale under different heavy metal stressors. The results showed that the endophytic fungal diversity decreased compared with the control under the different heavy metals stressors, while the diversity of endophytic bacteria showed an increasing trend. The biomarker analysis indicated that Zn and Pb stress led to obvious branches. Specific OTUs analysis showed that there were 1224, 597, and 1004 OTUs specific under Zn, Pb, and Cd stress in the bacterial community and 135, 81, and 110 OTUs specific under Zn, Pb, and Cd stress in the fungal community. The co-occurrence network showed changes in microbial interactions under heavy metal contamination conditions, suggesting that endophytic bacteria play an important role in the resistance of host plants. The Spearman analysis showed that the correlation between endophytic bacteria and endophytic fungi in relation to heavy metal transport exhibited variations. Our results expand the knowledge of the relationships of plant-microbe interactions and offer pivotal information to reveal the role of endophytes under different heavy metal stress conditions.

Development of transgenic Brassica napus plants with AtATM3 gene to enhance cadmium and lead tolerance

Four popular genotypes of Brassica napus, cv. BARI Sarisha-8, BARI Sarisha-13, Binasarisha-4, and Binasarisha-8 were subjected to cadmium (Cd) and lead (Pb) stress to identify a genotype with enhanced tolerance of Cd and Pb. The goal was to use the selected genotype for genetic engineering, thereby improving traits related to heavy metal tolerance and accumulation to remediate polluted agricultural soils. The genotype, BARI Sarisha-8 with superior tolerance to both Cd and Pb stresses, was chosen for genetic engineering with Arabidopsis thaliana ABC transporter of the mitochondrion 3 (AtATM3) gene. The transformation process involved coculturing the cotyledon explants with Agrobacterium strain GV3101 carrying a binary vector containing the hygromycin phosphotransferase (HPT) gene as a selectable marker and the AtATM3 gene. Transformation efficiency was significantly enhanced with a two-day co-cultivation period on shoot induction medium composed of MS medium, α-naphthaleneacetic acid (0.5 mg/L), and 6-benzyladenine (3 mg/L), supplemented with acetosyringone (20 mg/L), along with a four-day delay in exposing the explants to the selective agent hygromycin. Hygromycin-resistant shoots were obtained by employing a three-step selection process. The refined protocol resulted in a transformation efficiency of 15.38%. Polymerase chain reaction (PCR) analysis confirmed the integration of AtATM3 and HPT genes into the host genome in all recombinant plants. Transgenic B. napus plants expressing the AtATM3 gene exhibited notable improvements in tolerance, demonstrating a 1.4- to 1.7fold increase in Cd tolerance and a 1.3- to 1.5-fold increase in Pb tolerance compared to the wild type (nontransformed) under both Cd and Pb stress conditions.

Data notes on the proteomics of Dendrobium huoshanense under pb treatment.

Pb stress has a negative impact on plant growth by interfering with photosynthesis and releasing reactive oxygen species, causing major risks such as heavy metal ion accumulation in the soil matrix. A proteomics experiment was conducted to determine whether protein levels of Dendrobium huoshanense changed in response to Pb stress seven to fifteen days after being sprayed with a 200mg/L Pb (NO3)2 solution. The proteomic data we gathered provides a model for investigations into the mechanisms underlying Dendrobium plant resistance to heavy metal stress. A label-free quantitative proteomics approach was employed to examine the variations in protein expression levels of D. huoshanense at different times of Pb(NO3)2 treatment. We submitted the raw data obtained from these proteomics sequencing experiments to the ProteomeXchange database with the accession number PXD047050. 63,194 mass spectra in total were compared after being imported into the Proteome Discoverer software for database search. A total of 12,402 spectral peptides were identified with a confidence level exceeding 99%, which resulted in the identification of 2,449 significantly differential proteins. These proteins can be utilized for screening, functional annotation, and enrichment analysis of differentially expressed proteins before and after heavy metal treatment experiments.

Transcriptomics Combined with Physiology and Metabolomics Reveals the Mechanism of Tolerance to Lead Toxicity in Maize Seedling.

Lead (Pb) exposure can induce molecular changes in plants, disrupt metabolites, and impact plant growth. Therefore, it is essential to comprehend the molecular mechanisms involved in Pb tolerance in plants to evaluate the long-term environmental consequences of Pb exposure. This research focused on maize as the test subject to study variations in biomass, root traits, genes, and metabolites under hydroponic conditions under Pb conditions. The findings indicate that high Pb stress significantly disrupts plant growth and development, leading to a reduction in catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) activities by 17.12, 5.78, and 19.38%, respectively. Conversely, Pb stress led to increase malondialdehyde (MDA) contents, ultimately impacting the growth of maize. The non-targeted metabolomics analysis identified 393 metabolites categorized into 12 groups, primarily consisting of organic acids and derivatives, organ heterocyclic compounds, lipids and lipid-like molecules and benzenoids. Further analysis indicated that Pb stress induced an accumulation of 174 metabolites mainly enriched in seven metabolic pathways, for example phenylpropanoid biosynthesis and flavonoid biosynthesis. Transcriptome analysis revealed 1933 shared differentially expressed genes (DEGs), with 1356 upregulated and 577 downregulated genes across all Pb treatments. Additionally, an integrated analysis identified several DEGs and differentially accumulated metabolites (DAMs), including peroxidase, alpha-trehalose, and D-glucose 6-phosphate, which were linked to cell wall biosynthesis. These findings imply the significance of this pathway in Pb detoxification. This comprehensive investigation, employing multiple methodologies, provides a detailed molecular-level insight into maize's response to Pb stress.

Chlorophyll biosynthesis suppression, oxidative level and cell cycle arrest caused by Ni, Cr and Pb stress in maize exposed to treated soil from the Ferronikel smelter in Drenas, Kosovo

Although certain trace elements are essential for normal plant functionality, an excessive increase in their concentration can disrupt plant development and physiology due to phytotoxicity. This study aims to determine the toxic tolerance limits for different concentrations of Ni and Cr (50, 100, 200, and 400 ppm) and Pb (20, 50, 100, and 200 ppm) in maize seedlings grown in soil collected near the Ferronikel smelter in Drenas, Kosovo. We will assess these limits using sensitive biomarkers, including δ-aminolevulinic acid dehydratase (ALA-D) activity, δ-aminolevulinic acid (ALA) content, chlorophyll content, glutathione (GSH) levels, and lipid peroxidation (MDA), as well as by evaluating DNA content and cell cycle dynamics. All the investigated heavy metals showed a significant increase in concentration in leaves; in particular, Ni showed a strong significant association between its concentration in treatment and in the leaves. At concentrations of 400 ppm, Ni and Cr had significant negative effects on all biomarkers, with ALA-D activity inhibited by up to 50%, and total chlorophyll content significantly decreased. A robust correlation was observed between Ni and Cr and the level of cellular oxidative stress in leaves, as monitored through GSH, lipid peroxidation, and ALA levels. Additionally, the cell cycle, especially in the G1 and G2/M phases, was arrested. These findings emphasize the significant adverse impact of high concentrations of Ni and Cr in plant metabolism. This research contributes to our understanding of managing and mitigating heavy metal contamination in agricultural areas and its potential implications for plant defense mechanisms.

Genome-wide identification and characterization of NAC transcription factor family members in Trifolium pratense and expression analysis under lead stress

BackgroundThe NAC TF family is widely involved in plant responses to various types of stress. Red clover (Trifolium pratense) is a high-quality legume, and the study of NAC genes in red clover has not been comprehensive. The aim of this study was to analyze the NAC gene family of red clover at the whole-genome level and explore its potential role in the Pb stress response.ResultsIn this study, 72 TpNAC genes were identified from red clover; collinearity analysis showed that there were 5 pairs of large fragment replicators of TpNAC genes, and red clover was found to be closely related to Medicago truncatula. Interestingly, the TpNAC genes have more homologs in Arabidopsis thaliana than in soybean (Glycine max). There are many elements in the TpNAC genes promoters that respond to stress. Gene expression analysis showed that all the TpNAC genes responded to Pb stress. qRT-PCR showed that the expression levels of TpNAC29 and TpNAC42 were significantly decreased after Pb stress. Protein interaction network analysis showed that 21 TpNACs and 23 other genes participated in the interaction. In addition, the TpNAC proteins had three possible 3D structures, and the secondary structure of these proteins were mainly of other types. These results indicated that most TpNAC members were involved in the regulation of Pb stress in red clover.ConclusionThese results suggest that most TpNAC members are involved in the regulation of Pb stress in red clover. TpNAC members play an important role in the response of red clover to Pb stress.

Competition of Cd(II) and Pb(II) on the bacterial cells: a new insight from bioaccumulation based on NanoSIMS imaging.

Polymetallic exposure causes complex toxicity to microorganisms. In this study, we investigated the responses of Escherichia coli under co-existence of cadmium (Cd) and lead (Pb), primarily based on biochemical analysis and RNA sequencing. Cd completely inhibited bacterial growth at a concentration of 2.41 mmol/L, with its removal rate as low as <10%. In contrast, the Pb removal rate was >95% under equimolar sole Pb stress. In addition, the Raman analysis confirmed the loss of proteins for the bacterial cells. Under the co-existence of Cd and Pb, the Cd toxicity to E. coli was alleviated. Meanwhile, the biosorption of Pb cations was more intense during the competitive sorption with Cd. Transmission electron microscopy images showed that a few cells were elongated during incubation, i.e., the average cellular length increased from 1.535 ± 0.407 to 1.845 ± 0.620 µm. Moreover, NanoSIMS imaging showed that the intracellular distribution of Cd and Pb was coupled with sulfur. Genes regulating sulfate transporter were also upregulated to promote sulfate assimilation. Then, the subsequent production of biogenic sulfide and sulfur-containing amino acids was enhanced. Although this strategy based on S enrichment could resist the polymetallic stress, not all related genes were induced to upregulate under sole Cd stress. Therefore, the S metabolism might remodel the microbial resistance to variable occurrence of heavy metals. Furthermore, the competitive sorption (in contrast to sole Cd stress) could prevent microbial cells from strong Cd toxicity.IMPORTANCEMicrobial tolerance and resistance to heavy metals have been widely studied under stress of single metals. However, the polymetallic exposure seems to prevail in the environment. Though microbial resistance can alleviate the effects of exogenous stress, the taxonomic or functional response to polymetallic exposure is still not fully understood. We determined the strong cytotoxicity of cadmium (Cd) on growth, and cell elongation would be driven by Cd stress. The addition of appropriate lead (Pb) showed a stimulating effect on microbial bioactivity. Meanwhile, the biosorption of Pb was more intense during co-existence of Pb and Cd. Our work also revealed the spatial coupling of intracellular S and Cd/Pb. In particular, the S assimilation was promoted by Pb stress. This work elucidated the microbial responses to polymetallic exposure and may provide new insights into the antagonistic function during metal stresses.

Unlocking the phytoremediation potential of organic acids: A study on alleviating lead toxicity in canola (Brassica napus L.)

Soil contamination with toxic heavy metals [such as lead (Pb)] is becoming a serious global problem due to the rapid development of the social economy. Organic chelating agents such as maleic acid (MA) and tartaric acid (TA) are more efficient, environmentally friendly, and biodegradable compared to inorganic chelating agents and they enhance the solubility, absorption, and stability of metals. To investigate this, we conducted a hydroponic experiment to assess the impact of MA (0.25 mM) and TA (1 mM) on enhancing the phytoremediation of Pb under its toxic concentration of 100 μM, using the oil seed crop canola (Brassica napus L.). Results from the present study showed that the Pb toxicity significantly (P < 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes and nutritional contents from the roots and shoots of the plants. In contrast, toxic concentration of Pb significantly (P < 0.05) increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, increased enzymatic and non-enzymatic antixoidants and their specific gene expression and also increased organic acid exudation patter in the roots of B. napus. In addition, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that Pb toxicity significantly affected double membranous organelles while Fourier-transform infrared (FTIR) spectroscopy showed an nveiled distinct peak variations in Pb-treated plants, when compared to control. Additionally, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that Pb toxicity significantly affected double-membrane organelles, while Fourier-transform infrared (FTIR) spectroscopy unveiled distinct peak variations in Pb-treated plants compared to the control. The negative impact of Pb toxicity can overcome the application of MA and TA, which ultimately increased plant growth and biomass by capturing the reactive oxygen species, and decreased oxidative stress in B. napus. With the application of MA and TA, the values of the bioaccumulation factor (BAF) and translocation factor (TF) exceeded 1, indicating that the use of MA and TA enhances the phytoremediation potential of B. napus under Pb stress conditions. This finding could be beneficial for field environment studies, especially when explored through in-depth genetic and molecular analysis.

A comparative in vitro study of Pb tolerance in three sugarcane (Saccharum officinarum L.) genotypes

Heavy metal accumulation in agriculture land is one of the major agriculture challenges affecting the crop production and threatens the food safety. A comparative analysis was conducted to assess the tolerance of three sugarcane (Saccharum officinarum L.) genotypes to Lead nitrate under controlled in vitro conditions. Various parameters including fresh and dry weight, callus morphology, shoot morphology, protein contents, catalase, superoxide dismutase, peroxidase, ascorbic acid contents, relative growth rate, stress tolerance index, Pb contents, and Bio concentration factor were evaluated across a range of six different concentrations of Pb (0, 0.1, 0.2, 0.3, 0.4, 0.5, 1 mM). Lead had a noticeable impact on callus growth and regeneration across all three genotypes, whereas it did not significantly affect root regeneration. All genotypes significantly vary at each treatment and parameter except Bio-concentration factor and protein contents. Among the genotypes studied, YT-53 exhibited the highest resistance to Pb-induced stress, followed by CP-77400, while NSG-59 demonstrated the least resistance to Pb stress. Most resistant genotypes can be used in heavy metal effected area for better yield and phytoremediation in Pb affected soil and in other breeding programs.

Physiological response and phytoremediation potential of dioecious Hippophae rhamnoides inoculated with arbuscular mycorrhizal fungi to Pb and Zn pollution.

Plant-microorganism combined remediation of heavy metal pollution has been reported, but little attention has been paid to the effect of arbuscular mycorrhizal (AM) fungi on phytoremediation of dioecious plants under heavy metal pollution. In this study, the growth, physiological responses and phytoremediation traits of Hippophae rhamnoides were determined to evaluate whether sex-specific ecophysiological responses and phytoremediation capacities of females and males are affected by additional AM fungi (Glomus mosseae) under heavy metal treatments. The results showed that excess Pb and Zn stresses inhibited photosynthetic capacities of both sexes. However, inoculated AM fungi treatment increased the activity of photosynthesis, content of photosynthetic pigment, activity of superoxide dismutase, the content of proline and root Pb content and enrichment coefficient of males while decreased root Pb content of females under Pb stress. On the other hand, inoculated AM fungi treatment increased the photosynthetic activities and Pro accumulation of females, and activity of superoxide dismutase and transport coefficient of males under Zn stress. These results demonstrate that H. rhamnoides inoculated AM fungi showed significant sex-specific responses on the growth, physiological traits and phytoremediation potential to Pb and Zn stress. AM fungi significantly improved the tolerance of males to Pb stress and both sexes to Zn stress, which indicates H. rhamnoides and AM fungi can be used as a plant-microbial combined remediation method for Pb and Zn contaminated soil. More attention should be paid on sexual-specific responses and phytoremediation of dioecious plants to heavy metals in the future.

Unveiling the Effect of EDTA and SA in Mustard under Cd and Pb Stress

Unveiling the Effect of EDTA and SA in Mustard under Cd and Pb Stress

Stress-mitigating behavior of glycine betaine to enhance growth performance by suppressing the oxidative stress in Pb-stressed barley genotypes.

The toxicity of lead (Pb) in agricultural soil is constantly increasing as a result of anthropogenic activities. Pb is one of the most phytotoxic metals in soil that accumulates in plant tissue, resulting in yield loss. It is currently becoming more popular to supplement glycine betaine (GB) for Pb-induced stress tolerance in crop plants. Currently, no report describes the use of GB as a stress mitigator for growth attributes and stress-specific biomarkers in barley plants under Pb stress conditions. Hence, the present research was designed to examine the stress-mitigating behavior of GB on various growth attributes including germination percentage, seed vigor index (SVI), radicle length, plant biomass (fresh and dry), shoot and root length, physiological attributes such as relative water content (RWC), and stress-specific biomarkers like electrolyte leakage (EL), and H2O2 content of two barley varieties viz. BH959 and BH946 at three Pb stress treatments (15mM, 25mM, and 35mM), with and without GB (2mM) supplementation in natural conditions. The present investigation showed that at the highest Pb stress (35mM), the germination rate was reduced to zero, and the growth attributes and RWC of both barley varieties were also reduced as compared to the non-stressed plants (control) with an increase in Pb treatment. However, EL up to 70% and H2O2 content up to 30% increased with an increase in Pb stress concentration indicated by ROS accumulation, resulting in more oxidative stress. Additionally, GB application alleviated the toxic effect of Pb stress by improving the rate of germination by 33.3% and growth performance by reducing the ROS accumulation in terms of reducing stress biomarkers H2O2 by 25%, and EL by 12%. It has been revealed that the application of GB can minimize or reduce the toxic effects caused by Pb toxicity in both varieties, positively modulating plant growth performances and lowering oxidative stress. This research may provide a scientific basis for assessing Pb tolerance in barley plants and developing alternative approaches to protecting them from the severe effects of Pb toxicity.

Exogenous application of jasmonates and brassinosteroids alleviates lead toxicity in bamboo by altering biochemical and physiological attributes.

Exogenous application of phytohormones is getting promising results in alleviating abiotic stresses, particularly heavy metal (HMs). Jasmonate (JA) and brassinosteroid (BR) have crosstalk in bamboo plants, reflecting a burgeoning area of investigation. Lead (Pb) is the most common pollutant in the environment, adversely affecting plants and human health. The current study focused on the foliar application of 10µM JA and 10µM BR in both single and combination forms on bamboo plants grown under Pb stress (0, 50, 100, 150µM) with a completely randomized design by four replications. The study found that applying 10µM JA and 10µM BR significantly improves growth and tolerance by reducing oxidative stress, reactive oxygen species including hydrogen peroxide (H2O2, 32.91%), superoxide radicals (O2-•, 33.9%), methylglyoxal (MG, 19%), membrane lipoperoxidation (25.66%), and electrolyte leakage (41.5%) while increasing antioxidant (SOD (18%), POD (13%), CAT (20%), APX (12%), and GR (19%)), non-antioxidant (total phenolics (7%), flavonols (12.3%), and tocopherols (13.8%)), and glyoxylate activity (GLyI (13%), GLyII (19%)), proline content (19%), plant metal chelating capacity (17.3%), photosynthetic pigments (16%), plant growth (10%), and biomass (12%). We found that JA and BR, in concert, boost bamboo species' Pb tolerance by enhancing antioxidant and glyoxalase cycles, ion chelation, and reducing metal translocation and accumulation. This conclusively demonstrates that utilizing a BR-JA combination form at 10µM dose may have the potential to yield optimal efficiency in mitigating oxidative stress in bamboo plants.

Different responses of Sinorhizobium sp. upon Pb and Zn exposure: Mineralization versus complexation

Lead (Pb) and zinc (Zn) have been discharged into environment and may negatively impact ecological security. Rhizobia has gained attention due to their involvement in the restoration of metal polluted soils. However, little is known about the responses of rhizobia under Pb and Zn stress, especially the roles played by extracellular polymeric substances (EPS) in the resistance of these two metals. Here, Sinorhizobium sp. C10 was isolated from soil around a mining area and was exposed to a series of Pb/Zn treatments. The cell morphology and surface mineral crystals, EPS content and fluorescent substances were determined. In addition, the extracellular polysaccharides and proteins were characterized by attenuated total reflection infrared spectroscopy (ATR-IR) and X-ray photoelectron spectroscopy (XPS). The results showed that Zn stress induced the synthesis of EPS by C10 cells. Functional groups of polysaccharides (CO) and proteins (C–O/C–N) were involved in complexation with Zn. In contrast, C10 resisted Pb stress by forming lead phosphate (Pb3(PO4)2) on the cell surface. Galactose (Gal) and tyrosine played key roles in resistance to the Zn toxicity, whereas glucosamine (N-Glc) was converted to glucose in large amounts during extracellular Pb precipitation. Together, this study demonstrated that C10 possessed different strategies to detoxify the two metals, and could provide basis for bioremediation of Pb and Zn polluted sites.

Transcriptome-wide m6A methylation profiling identifies GmAMT1;1 as a promoter of lead and cadmium tolerance in soybean nodules

Lead (Pb) and cadmium (Cd) are common heavy metal pollutants that are often found in the soil in soybean agricultural production, adversely impacting symbiotic nitrogen fixation in soybean nodules. In this study, the exposure of soybean nodules to Pb and Cd stress was found to reduce nitrogenase activity. Shifts in the RNA methylation profiles of nodules were subsequently examined by profiling the differential expression of genes responsible for regulating m6A modifications and conducting transcriptome-wide analyses of m6A methylation profiles under Pb and Cd stress condition. Differentially methylated genes (DMGs) that were differentially expressed were closely related to reactive oxygen species activity and integral membrane components. Overall, 19 differentially expressed DMGs were ultimately determined to be responsive to both Pb and Cd stress, including Glyma.20G082450, which encodes GmAMT1;1 and was confirmed to be a positive regulator of nodules tolerance to Pb and Cd. Together, these results are the first published data corresponding to transcriptome-wide m6A methylation patterns in soybean nodules exposed to Cd and Pb stress, and provide novel molecular insight into the regulation of Pb and Cd stress responses in nodules, highlighting promising candidate genes related to heavy metal tolerance, that may also be amenable to application in agricultural production. Environmental implicationsLead (Pb) and cadmium (Cd) are prevalent heavy metal pollutants in soil, and pose a major threat to crop production, food security and human health. Here, MeRIP-seq approach was employed to analyze the regulatory network activated in soybean nodules under Pb and Cd stress, ultimately leading to the identification of 19 shared differentially expressed DMGs. When overexpressed, GmATM1;1 was found to enhance the Pb and Cd tolerance of soybean nodules. These results provide a theoretical basis for studies on tolerance to heavy metals in symbiotic nitrogen fixation, and provide an approach to enhancing Pb and Cd tolerance in soybean production.

Foliar spraying of indoleacetic acid (IAA) enhances the phytostabilization of Pb in naturally tolerant ryegrass by limiting the root-to-shoot transfer of Pb and improving plant growth.

Exogenous addition of IAA has the potential to improve the metal tolerance and phytostabilization of plants, but these effects have not been systematically investigated in naturally tolerant plants. Ryegrass (Lolium perenne L.) is a typical indigenous plant in the Lanping Pb/Zn mining area with high adaptability. This study investigated the phytostabilization ability and Pb tolerance mechanism of ryegrass in response to Pb, with or without foliar spraying of 0.1 mmol L-1 IAA. The results indicated that appropriate IAA treatment could be used to enhance the phytostabilization efficiency of naturally tolerant plants. Foliar spraying of IAA increased the aboveground and belowground biomass of ryegrass and improved root Pb phytostabilization. Compared to Pb-treated plants without exogenous IAA addition, Pb concentration in the shoots of ryegrass significantly decreased, then increased in the roots after the foliar spraying of IAA. In the 1,000 mg kg-1 Pb-treated plants, Pb concentration in the shoots decreased by 69.9% and increased by 79.1% in the roots after IAA treatment. IAA improved plant growth, especially in soils with higher Pb concentration. Foliar spraying of IAA increased shoot biomass by 35.9% and root biomass by 109.4% in 1,000 mg kg-1 Pb-treated plants, and increased shoot biomass by 196.5% and root biomass by 71.5% in 2,000 mg kg-1 Pb-treated plants. In addition, Pb stress significantly decreased the content of photosynthetic pigments and anti-oxidase activities in ryegrass, while foliar spraying of IAA remedied these negative impacts. In summary, foliar spraying of IAA could increase the biomass and improve the Pb tolerance of ryegrass.

Enhancing lead removal from wastewater and alleviating lead stress in soil-wheat systems using starch-stabilized Fe-Ni/biochar composites: Synthesis and physico-chemical investigations

In this study, starch-stabilized and Fe/Ni bimetal modified biochar composites of StFeNi-BC and StFeNi-BC-350 were successfully fabricated and applied in removing Pb(II) from aqueous solutions. The absorption of Pb(II) by StFeNi-BC and StFeNi-BC-350 were controlled by monolayer chemisorption and their maximum adsorption capacities were 122.767 and 148.043 mg/g, respectively. Mechanism studies showed that electrostatic attraction, ion exchange, complexation and physical adsorption occurred on the adsorbent surface. Studies on the influence of co-existing metal ions and water matrices on adsorption of Pb(II) demonstrated that StFeNi-BC-350 displayed high anti-interfering ability and promising application prospect for Pb(II) removal. In addition, StFeNi-BC-350 was applied in soil-wheat pot systems to further investigate its influence on reducing Pb induced oxidative stress on wheat. Compared with the control, the addition of StFeNi-BC-350 increased the biomass and total chlorophyll content in leaves, and decreased the activity of antioxidant enzymes (MDA, SOD, CAT, POD) together with ROS fluorescence intensity of wheat. The results indicated that StFeNi-BC-350 could alleviate Pb(II) stress of wheat. Furthermore, the addition of StFeNi-BC-350 improved the physicochemical properties of the soil, and increased the abundance as well as the number of soil microorganisms, thereby alleviating Pb stress on wheat. Therefore, StFeNi-BC-350 is suitable for the practical treatment of Pb-contaminated water and soil.

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

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.

Physiological tolerance of black locust (Robinia pseudoacacia L.) and changes of rhizospheric bacterial communities in response to Cd and Pb in the contaminated soil.

Woody plants possess great potential for phytoremediation of heavy metal-contaminated soil. A pot trial was conducted to study growth, physiological response, and Cd and Pb uptake and distribution in black locust (Robinia pseudoacacia L.), as well as the rhizosphere bacterial communities in Cd and Pb co-contaminated soil. The results showed that R. pseudoacacia L. had strong physiological regulation ability in response to Cd and Pb stress in contaminated soil. The total chlorophyll, malondialdehyde (MDA), soluble protein, and sulfhydryl contents, as well as antioxidant enzymes (superoxide dismutase, peroxidase, catalase) activities in R. pseudoacacia L. leaves under the 40mg·kg-1 Cd and 1000mg·kg-1 Pb co-contaminated soil were slightly altered. Cd uptake in R. pseudoacacia L. roots and stems increased, while the Pb content in the shoots of R. pseudoacacia L. under the combined Cd and Pb treatments decreased in relative to that in the single Pb treatments. The bacterial α-diversity indices (e.g., Sobs, Shannon, Simpson, Ace, and Chao) of R. pseudoacacia L. rhizosphere soil under Cd and Pb stress were changed slightly relative to the CK treatment. However, Cd and Pb stress could significantly (p < 0.05) alter the rhizosphere soil microbial communities. According to heat map and LEfSe(Linear discriminant analysis Effect Size) analysis, Bacillus, Sphingomonas, Terrabacter, Roseiflexaceae, Paenibacillus, and Myxococcaceae at the genus level were notably (p < 0.05) accumulated in the Cd- and/or Pb-contaminated soil. Furthermore, the MDA content was notably (p < 0.05) negatively correlated with the relative abundances of Isosphaeraceae, Gaiellales, and Gemmatimonas. The total biomass of R. pseudoacacia L. was positively (p < 0.05) correlated with the relative abundances of Xanthobacteraceae and Vicinamibacreraceae. Network analysis showed that Cd and Pb combined stress might enhance the modularization of bacterial networks in the R. pseudoacacia L. rhizosphere soil. Thus, the assembly of the soil bacterial communities in R. pseudoacacia L. rhizosphere may improve the tolerance of plants in response to Cd and/or Pb stress.