Impact of lead tolerant plant growth promoting rhizobacteria on growth, physiology, antioxidant activities, yield and lead content in sunflower in lead contaminated soil

Molecular and eco-physiological responses of soil-borne lead (Pb2+)-resistant bacteria for bioremediation and plant growth promotion under lead stress

Lead (Pb) is the 2nd known portentous hazardous substance after arsenic (As). Being highly noxious, widespread, non-biodegradable, prolonged environmental presence, and increasing accumulation, particularly in arable land, Pb pollution has become a serious global health concern requiring urgent remediation. Soil-borne, indigenous microbes from Pb-polluted sites have evolved diverse resistance strategies, involving biosorption, bioprecipitation, biomineralization, biotransformation, and efflux mechanisms, under continuous exposure to Pb in human-impacted surroundings. These strategies employ a wide range of functional bioligands to capture Pb and render it inaccessible for leaching. Recent breakthroughs in molecular technology and understanding of lead resistance mechanisms offer the potential for utilizing microbes as biological tools in environmental risk assessment. Leveraging the specific affinity and sensitivity of bacterial regulators to Pb2+ ions, numerous lead biosensors have been designed and deployed worldwide to monitor Pb bioavailability in contaminated sites, even at trace levels. Besides, the ongoing degradation of croplands due to Pb pollution poses a significant challenge to meet the escalating global food demands. The accumulation of Pb in plant tissues jeopardizes both food safety and security while severely impacting plant growth. Exploring Pb-resistant plant growth-promoting rhizobacteria (PGPR) presents a promising sustainable approach to agricultural practices. The active associations of PGPR with host plants have shown enhancements in plant biomass and stress alleviation under Pb influence. They thus serve a dual purpose for plants grown in Pb-contaminated areas. This review aims to offer a comprehensive understanding of the role played by Pb-resistant soil-borne indigenous bacteria in expediting bioremediation and improving the growth of Pb-challenged plants essential for potential field application, thus broadening prospects for future research and development.

The First Pseudomonas Phage vB_PseuGesM_254 Active against Proteolytic Pseudomonas gessardii Strains

Bacteria of the Pseudomonas genus, including the Pseudomonas gessardii subgroup, play an important role in the environmental microbial communities. Psychrotolerant isolates of P. gessardii can produce thermostable proteases and lipases. When contaminating refrigerated raw milk, these bacteria spoil it by producing enzymes resistant to pasteurization. One possible way to prevent spoilage of raw milk is to use Pseudomonas lytic phages specific to undesirable P. gessardii isolates. The first phage, Pseudomonas vB_PseuGesM_254, was isolated and characterized, which is active against several proteolytic P. gessardii strains. This lytic myophage can infect and lyse its host strain at 24 °C and at low temperature (8 °C); so, it has the potential to prevent contamination of raw milk. The vB_PseuGesM_254 genome, 95,072 bp, shows a low level of intergenomic similarity with the genomes of known phages. Comparative proteomic ViPTree analysis indicated that vB_PseuGesM_254 is associated with a large group of Pseudomonas phages that are members of the Skurskavirinae and Gorskivirinae subfamilies and the Nankokuvirus genus. The alignment constructed using ViPTree shows that the vB_PseuGesM_254 genome has a large inversion between ~53,100 and ~70,700 bp, which is possibly a distinctive feature of a new taxonomic unit within this large group of Pseudomonas phages.

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.

Phytomelatonin maintained chromium toxicity induced oxidative burst in Brassica juncea L. through improving antioxidant system and gene expression

Chromium (Cr) contamination in soils reduces crop yields and poses a remarkable risk to human and plant system. The main objective of this study was to observe the protective mechanisms of exogenously applied melatonin (Mel- 0.05, 0.1, and 0.15 μM) in seedlings of Brassica juncea L. under Cr (0.2 mM) stress. This was accomplished by analysing the plant's morpho-physiological, biochemical, nuclear, membrane, and cellular characteristics, as well as electrolyte leakage. Superoxide, malondialdehyde, and hydrogen peroxide increased with Cr toxicity. Cr also increased electrolyte leakage. Seedlings under Cr stress had 86.4% more superoxide anion and 27.4% more hydrogen peroxide. Electrolyte leakage increased 35.7% owing to Cr toxicity. B. juncea L. cells with high radical levels had membrane and nuclear damage and decreased viability. Besides this, the activities of the antioxidative enzymes, as POD, APOX, SOD, GST, DHAR, GPOX and GR also elevated in the samples subjected to Cr toxicity. Conversely, the activity of catalase was downregulated due to Cr toxicity. In contrast, Mel reduced oxidative damage and conserved membrane integrity in B. juncea seedlings under Cr stress by suppressing ROS generation. Moreover, the activity of antioxidative enzymes that scavenge reactive oxygen species was substantially upregulated by the exogenous application of Mel. The highest concentration of Mel (Mel c- 0.15 μM) applied showed maximum ameliorative effect on the toxicity caused by Cr. It causes alleviation in the activity of SOD, CAT, POD, GPOX, APOX, DHAR, GST and GR by 51.32%, 114%, 26.44%, 48.91%, 87.51%, 149%, 42.30% and 40.24% respectively. Histochemical investigations showed that Mel increased cell survival and reduced ROS-induced membrane and nuclear damage. The findings showed that Mel treatment upregulated several genes, promoting plant development. Its supplementation decreased RBOH1 gene expression in seedling sunder stress. The results supported the hypothesis that Mel concentrations reduce Cr-induced oxidative burst in B. juncea.

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

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

Exploring the synergistic effect of chromium (Cr) tolerant Pseudomonas aeruginosa and nano zero valent iron (nZVI) for suppressing Cr uptake in Aloe Vera

Chromium (Cr) contamination of soil has substantially deteriorated soil health and has interfered with sustainable agricultural production worldwide and therefore, its remediation is inevitable. Inoculation of plant growth promoting rhizobacteria (PGPR) in association with nanotechnology has exerted broad based impacts in agriculture, and there is an urgent need to exploit their synergism in contaminated soils. Here, we investigated the effect of co-application of Cr-tolerant "Pseudomonas aeruginosa CKQ9" strain and nano zerovalent iron (nZVI) in improving the phytoremediation potential of aloe vera (Aloe barbadensis L.) under Cr contamination. Soil was contaminated by using potassium dichromate (K2Cr2O7) salt and 15 mg kg-1 contamination level in soil was maintained via spiking and exposure to Cr lasted throughout the duration of the experiment (120 days). We observed that the co-application alleviated the adverse impacts of Cr on aloe vera, and improved various plant attributes such as plant height, root area, number of leaves and gel contents by 51, 137, 67 and 49% respectively as compared to control treatment under Cr contamination. Similarly, significant boost in the activities of various antioxidants including catalase (124%), superoxide dismutase (87%), ascorbate peroxidase (36%), peroxidase (89%) and proline (34%) was pragmatic under contaminated soil conditions. In terms of soil Cr concentration and its plant uptake, co-application of P. aeruginosa and nZVI also reduced available Cr concentration in soil (50%), roots (77%) and leaves (84%), while simultaneously increasing the relative production index by 225% than un-inoculated control. Hence, integrating PGPR with nZVI can be an effective strategy for enhancing the phytoremediation potential of aloe vera.

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.

Pseudomonas fluorescens and L-tryptophan application triggered the phytoremediation potential of sunflower (Heliantus annuus L.) in lead-contaminated soil

Lead, a toxic heavy metal present in soil, hampers biological activities and affects the metabolism of plants, animals, and human beings. Its higher concentration may disturb the various physio-chemical processes, which result in stunted and poor plant growth. An interactive approach of plant growth promoting rhizobacteria (PGPR) and L-tryptophan can be used to mitigate the lethal effects of lead. A pot experiment was conducted, and two weeks before sowing, the level of lead (300 mg kg-1) was maintained by spiking the PbCl2 salt. Pseudomonas fluorescens and L-tryptophan were applied individually as well as in combination to segregate the effect of both in contaminated soil under a completely Randomized Design (CRD). Statistical analysis revealed that plant growth was significantly reduced up to 22% due to lead contamination. However, the interactive approach of PGPR and L-tryptophan significantly improved the plant growth, physiology, and yield with relative productive index (RPI) under a lead-stressed environment. Moreover, integrated use of PGPR and L-tryptophan demonstrated a considerable increase (22%) in lead removal efficiency (LRE) by improving bioconcentration factor (BCF) and translocation factor (TF) for shoot without increasing the lead concentration in achenes. The reduced lead concentration in achene was due to its immobilization in shoot and root by negatively charged particles and improved the lead sequestration in vegetative parts which abridged the translocation of lead into achenes.

Effect of sodium alginate-gelatin-polyvinyl pyrrolidone microspheres on cucumber plants, soil, and microbial communities under lead stress

Lead is highly persistent and toxic in soil, hindering plant growth. Microspheres are a novel, functional, and slow-release preparation commonly used for controlled release of agricultural chemicals. However, their application in the remediation of Pb-contaminated soil has not been studied; furthermore, the remediation mechanism involved has not been systematically assessed. Herein, we evaluated the Pb stress mitigation ability of sodium alginate-gelatin-polyvinyl pyrrolidone composite microspheres. Microspheres effectively attenuated the Pb toxic effect on cucumber seedlings. Furthermore, they boosted cucumber growth, increased peroxidase activity, and chlorophyll content, while reducing malondialdehyde content in leaves. Microspheres promoted Pb enrichment in cucumber, especially in roots (about 4.5 times). They also improved soil physicochemical properties, promoted enzyme activity, and increased soil available Pb concentration in the short term. In addition, microspheres selectively enriched functional (heavy metal-tolerating and plant growth promoting) bacteria to adapt to and resist Pb stress by improving soil properties and nutrients. These results indicated that even a small amount (0.025-0.3 %) of microspheres can significantly reduce the adverse effects of Pb on plants, soil, and bacterial communities. Composite microspheres have shown great value in Pb remediation, and their application potential in phytoremediation is also worth evaluating to expand the application.

Effect of different levels of EDTA on phytoextraction of heavy metal and growth of Brassica juncea L

Heavy metal pollution of soil is a major concern due to its non-biodegradable nature, bioaccumulation, and persistence in the environment. To explore the probable function of EDTA in ameliorating heavy metal toxicity and achieve the sustainable development goal (SDG), Brassica juncea L. seedlings were treated with different concentrations of EDTA (0, 1.0, 2.0, 3.0, and 4.0 mM Kg-1) in heavy metal-polluted soil. Plant samples were collected 60 days after sowing; photosynthetic pigments, H2O2, monoaldehyde (MDA), antioxidant enzymes, and ascorbic acid content, as well as plant biomass, were estimated in plants. Soil and plant samples were also examined for the concentrations of Cd, Cr, Pb, and Hg. Moreover, values of the phytoremediation factor were utilized to assess the accumulation capacity of heavy metals by B. juncea under EDTA treatments. In the absence of EDTA, B. juncea seedlings accrued heavy metals in their roots and shoots in a concentration-dependent manner. However, the highest biomass of plants (roots and shoots) was recorded with the application of 2 mM kg-1 EDTA. Moreover, high levels (above 3 mM kg-1) of EDTA concentration have reduced the biomass of plants (roots and shoots), photosynthetic area, and chlorophyll content. The effect of EDTA levels on photosynthetic pigments (chlorophyll a and b) revealed that with an increment in EDTA concentration, accumulation of heavy metals was also increased in the plant, subsequently decreasing the chlorophyll a and b concentration in the plant. TLF was found to be in the order Pb> Hg> Zn> and >Ni, while TF was found to be in the order Hg>Zn>Ni>Pb, and the best dose was 3 mM kg-1 EDTA for Hg and 4 mM kg-1 for Pb, Ni, and Zn. Furthermore, hyperaccumulation of heavy metals enhanced the generation of hydrogen peroxide (H2O2), superoxide anions (O2•-), and lipid peroxidation. It also interrupts mechanisms of the antioxidant defense system. Furthermore, heavy metal stress reduced plant growth, biomass, and chlorophyll (chl) content. These findings suggest that the exogenous addition of EDTA to the heavy metal-treated seedlings increases the bioavailability of heavy metals for phytoextraction and decreases heavy metal-induced oxidative injuries by restricting heavy metal uptake and components of their antioxidant defense systems.

Evaluation of the motility and capacity of biofilm production by Pseudomonas fluorescens strains in residual milk

Pseudomonas fluorescens is known to have the ability to adhere and produce biofilm. The formation of biofilms is enhanced by cellular motility, particularly when mediated by flagella. Biofilm formed on surfaces such as those used for food production act as points of contamination, releasing pathogenic or deteriorating microorganisms and compromising the quality of products. We assessed two strains of Pseudomonas fluorescens PL5.4 and PL7.1, sampled from raw, chilled, buffalo milk, which was obtained from a dairy farm. Twitching and swarming motility assays were performed, in addition to the biofilm production evaluations at a temperature of 7 °C. Regarding the motility assays, only the PL5.4 strain scored positive for the swarming assay. On microplates, both strains presented themselves as strong biofilm producers at 7 °C. The PL5.4 strain was also able to form biofilm on a stainless steel structure and maintain this structure for up to 72 hours at refrigeration. The Pseudomonas fluorescens PL5.4 isolate was identified on the basis of a 99% sequence identity with Pseudomonas fluorescens A506, a strain used as a biocontrol in agriculture. Biofilm-forming bacteria, when adapted to low temperatures, become a constant source of contamination, damaging the production, quality, safety and shelf-life of products.

Application of ferromanganese functionalized biochar simultaneously reduces Cd and Pb uptake of wheat in contaminated alkaline soils

The reduction of Cd and Pb accumulation in wheat grains grown on Cd and Pb contaminated alkaline soils is a pressing issue that needs to be solved. In this study, ferromanganese functionalized biochar (FM-BC) was used to remediate Cd and Pb contaminated alkaline soils and mitigate Cd and Pb accumulation in wheat grains. The immobilization capacity and mechanism of FM-BC were investigated by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) characterization and chemical analysis. Fe and Mn loaded on FM-BC improved the removal efficiencies of DTPA-Cd and DTPA-Pb in soil with DTPA-Cd removal of 22.99%- 52.04% (JM22) and 25.54%- 53.32 (AK58) and DTPA-Pb removal of 11.39%- 22.36% (JM22) and 5.38%- 13.00% (AK58). The FT-IR and XRD results indicated that the complexation and precipitation of Cd and Pb with the Fe-Mn oxides and the oxygen-containing functional groups on biochar surface stabilized the Cd and Pb in soil for the observation of Cd₂Mn₃O₈, PbHPO₄, CdCO₃, and PbO₂ on FM-BC isolated from contaminated soils. FM-BC with excellent adsorption capacity reduced the available Cd and Pb in the soil, therefore, thereby inhibiting the Cd and Pb accumulation in wheat. In the 3% FM-BC treatment, Cd and Pb contents in wheat grains were lower than 0.10 mg/kg and 0.20 mg/kg, respectively, reaching the national safety standards. And FM-BC increased the Fe, Mn, Na and Zn contents in wheat grains, and improved the growth and yield of wheat. These findings suggest that FM-BC can be considered a prospective and effective material for remediation of alkaline soils contaminated with Cd and Pb.

Silicon fertilization enhances the resistance of tobacco plants to combined Cd and Pb contamination: Physiological and microbial mechanisms

Remediation of soil contaminated with cadmium (Cd) and lead (Pb) is critical for tobacco production. Silicon (Si) fertilizer can relieve heavy metal stress and promote plant growth, however, it remains unknown whether fertilization with Si can mitigate the effects of Cd and Pb on tobacco growth and alter microbial community composition in polluted soils. Here we assessed the effect of two organic (OSiFA, OSiFB) and one mineral Si fertilizer (MSiF) on Cd and Pb accumulation in tobacco plants, together with responses in plant biomass, physiological parameters and soil bacterial communities in pot experiments. Results showed that Si fertilizer relieved Cd and Pb stress on tobacco, thereby promoting plant growth: Si fertilizer reduced available Cd and Pb in the soil by 37.3 % and 28.6 %, respectively, and decreased Cd and Pb contents in the plant tissue by 42.0-55.5 % and 17.2-25.6 %, resulting in increased plant biomass by 13.0-30.5 %. Fertilization with Si alleviated oxidative damage by decreasing malondialdehyde content and increasing peroxidase and ascorbate peroxidase content. In addition, Si fertilization increased photosynthesis, chlorophyll and carotenoid content. Microbial community structure was also affected by Si fertilization. Proteobacteria and Actinobacteria were the dominant phylum in the Cd and Pb contaminated soils, but Si fertilization reduced the abundance of Actinobacteria. Si fertilization also altered microbial metabolic pathways associated with heavy metal resistance. Together, our results suggest that both organic and mineral Si fertilizers can promote tobacco growth by relieving plant physiological stress and favoring a heavy metal tolerant soil microbial community.

Burkholderia cepacia CS8 improves phytoremediation potential of Calendula officinalis for tannery solid waste polluted soil

Microbes have shown potential for the bioremediation of tannery waste polluted soil. During our previous study, it was observed that heavy metal resistant Burkholderia cepacia CS8 augmented growth and phytoremediation capability of an ornamental plant. Objective of the present research work was to evaluate the capability of B. cepacia CS8 assisted Calendula officinalis plants for the phytoremediation of tannery solid waste (TSW) polluted soil. The TSW treatment significantly reduced growth attributes and photosynthetic pigments in C. officinalis. However, supplementation of B. cepacia CS8 which exhibited substantial tolerance to the TSW amended soil, augmented growth traits, carotenoid, proline, and antioxidant enzymes level in C. officinalis under toxic and nontoxic regimes. Inoculation of B. cepacia CS8 augmented plant growth (shoot length 13%, root length 11%), physiological attributes (chlorophyll a 14%, chlorophyll b 17%), antioxidant enzyme activities (peroxidase 24%, superoxide dismutase 31% and catalase 19%), improved proline 36%, phenol 32%, flavonoids 14% and declined malondialdehyde (MDA) content 15% and hydrogen peroxide (H2O2) level 12% in C. officinalis at TSW10 stress compared with relevant un-inoculated plants of TSW10 treatment. Moreover, B. cepacia CS8 application enhanced labile metals in soil and subsequent metal uptake, such as Cr 19%, Cd 22%, Ni 35%, Fe 18%, Cu 21%, Pb 34%, and Zn 30%, respectively in C. officinalis plants subjected to TSW10 stress than that of analogous un-inoculated treatment. Higher plant stress tolerance and improved phytoremediation potential through microbial inoculation will assist in the retrieval of agricultural land in addition to the renewal of native vegetation.

Role of PGPR and silver nanoparticles on the physiology of Momordica charantia L. irrigated with polluted water comprising high Fe and Mn

The current investigation designed to estimate the bioremediation potential of plant growth-promoting rhizobacteria (PGPR) and Ag-nanoparticles. Tube well and HIT water comprising Mn and Fe above recommended values were used as treatments while tap water irrigation was treated as control. The HIT water showed 24, 200, and 64.11% higher content of Na, K Ca over control. Seeds were sterilized in 95% ethanol and soaked for 3 h before sowing in 73 h old culture of Pseudomonas stutzeri (Kx574858) @ 108 cells/ml. Phytotoxic effect of Fe and Mn reduce plant biomass and suppress photosynthetic activity indicates. The carotenoids, proline, and proline activity were 366, 450, and 678% higher in tube well water with combined PGPR and Ag-nanoparticles treatments. Pseudomonas stutzeri was more effective than Ag-nanoparticles to reduce oxidative stress with higher production of carotenoids, flavonoids, proline content, and enzyme SOD and CAT activities in HIT water. It is contingent that the high Mn and Fe bearing waste water enhance PGPR bioremediation potential to reduce metal stress in plants with synergistic action of PGPR and organic matter to alleviate oxidative stresses under metal stress. The residual effect of P. stutzeri on organic matter content of the rhizosphere soil and germination rate was higher for Momordica charantia L.

Characterization of Endophytic Bacteria Isolated from Typha latifolia and Their Effect in Plants Exposed to Either Pb or Cd

Plant-associated bacteria in heavy-metal-contaminated environments could be a biotechnological tool to improve plant growth. The present work aimed to isolate lead- and cadmium-tolerant endophytic bacteria from the roots of Typha latifolia growing in a site contaminated with these heavy metals. Endophytic bacteria were characterized according to Pb and Cd tolerance, plant-growth-promoting rhizobacteria activities, and their effect on T. latifolia seedlings exposed and non-exposed to Pb and Cd. Pb-tolerant isolates were identified as Pseudomonas azotoformans JEP3, P. fluorescens JEP8, and P. gessardii JEP33, while Cd-tolerant bacteria were identified as P. veronii JEC8, JEC9, and JEC11. They all exert biochemical activities, including indole acetic acid synthesis, siderophore production, and phosphate solubilization. Plant-bacteria interaction assays showed that P. azotoformans JEP3, P. fluorescens JEP8, P. gessardii JEP33, and P. veronii JEC8, JEC9, JEC11 promote the growth of T. latifolia seedlings by increasing the root and shoot length, while in plants exposed to either 5 mg/L of Pb or 10 mg/L of Cd, all bacterial isolates increased the shoot length and the number of roots per plant, suggesting that they are plant-growth-promoting rhizobacteria that could contribute to T. latifolia adaptation to the heavy metal polluted site.

Influence of Bacteria of the Genus Pseudomonas on Leguminous Plants and Their Joint Application for Bioremediation of Oil Contaminated Soils

The modern approach to the creation of biological products to stimulate plant growth is based on the study of specific inter-bacterial interactions. This study describes the impact that the introduction of strains of the genus Pseudomonas has on annual and perennial leguminous plants and the ecosystem of the leguminous plant-the indigenous microbial community. The objects of research under the conditions of vegetation experiments were plants of field peas (Pisum sativum L.), white lupine (Lupinus albus L.), chickpea (Cicer arietinum L.), alfalfa (Medicago sativa subsp. varia (Martyn) Arcang.), and white sweet clover (Melilotus albus Medik.). For the treatment of plant seeds, a liquid culture of strains of growth-stimulating bacteria Pseudomonas koreensis IB-4, and P. laurentiana ANT 17 was used. The positive effect of the studied strains on the germination, growth and development of plants was established. There was no inhibitory effect of inoculants on rhizobia; on the contrary, an increase in nodule formation was observed. The possibility of recultivation of oil-contaminated soil using chickpea and alfalfa as phytomeliorants and growth-stimulating strains P. koreensis IB-4, P. laurentiana ANT 17 as inoculants was evaluated. It is proved that seed treatment improved the morphological parameters of plants, as well as the efficiency of oil destruction.

Promising co-inoculation strategies to reduce arsenic toxicity in soybean

Arsenic (As) is the cause for concern worldwide due to its high toxicity. Its presence in agricultural soils and groundwater adversely affects soybean (Glycine max L.) growth and yield and also endangers food safety. Plant growth-promoting rhizobacteria (PGPR) could be used as part of cost-effective and eco-friendly strategies to mitigate As phytotoxicity. However, simple inoculation of soybean with PGPR Bradyrhizobium japonicum E109 (E109), a common practice in Argentina, is not effective in counteracting the effects of As exposure. Our aim was to assess whether the response of soybean to arsenate (AsV) and arsenite (AsIII) could be helpfully modulated by co-inoculating E109 with the free-living PGPRs Azospirillum brasilense Cd (Cd) or Bacillus pumilus SF5 (SF5). Co-inoculation with E109 + SF5 alleviated As-induced depletion of chlorophyll a and b, and carotenoid content, reaching an increase of 26, 28 y 31%, respectively. It also enhanced nodulation (15-19%) under As exposure. E109 + Cd and E109 + SF5 induced changes in the antioxidant system, which could be related to the maintenance of redox homeostasis. Moreover, As accumulation was reduced by 53% in aerial parts of plants inoculated with E109 + Cd, and by 16% in the roots of those inoculated with E109 + SF5. The strains selected show interesting potential for the development of biotechnological schemes to improve soybean yield while guaranteeing safer food production.

Insights on strain 115 plant growth-promoting bacteria traits and its contribution in lead stress alleviation in pea (Pisum sativum L.) plants

The present study aims to characterize the plant growth-promoting bacterial traits of Bacillus simplex (strain 115). This bacterium was inoculated in hydroponically conditions to improve pea (Pisum sativum L.) growth submitted to lead (Pb) toxicity. Root nodulation system was developed enough in 23-day-old plants attesting the interaction between the two organisms. In addition to its phosphate solubilization and siderophore production traits that reached 303.8 μg P mL-1 and 49.6 psu respectively, the Bacillus strain 115 exhibited Pb bio-sorption ability. Inoculation of Pb-stressed pea with strain 115 showed roots and shoots biomass recovery (+ 70% and + 61%, respectively). Similarly, water and protein contents were increased in Pb-treated plants after bacterial inoculation. In the presence of strain 115, Pb relative toxicity level decreased (- 39.3% compared to Pb stress only). Moreover, catalase and superoxide dismutase activities were upregulated in Pb-exposed plants (+ 56% and + 51%, respectively). After inoculation with strain 115, catalase and superoxide dismutase activities were restored by - 38% and - 44% respectively. Simultaneously, oxidant stress indicator (H2O2 and 4-hydroxynonenal) and osmo-regulators (proline and glycine-betaine) contents as well as lipoxygenase activity decreased significantly in Pb-treated plants after Bacillus strain's inoculation. Taken together, the results give some evidences for the plant growth-promoting capacity of strain 115 in helping alleviation of Pb stress.

Selecting Endophytes for Rhizome Production, Curcumin Content, Biocontrol Potential, and Antioxidant Activities of Turmeric (Curcuma longa)

Beneficial endophytes may enhance plant growth and stress tolerance. Yet, the plant health benefits of endophytes can be altered by biotic and abiotic factors and, thus, favour the inhibition of turmeric growth and curcumin production. The double petri dish method and greenhouse pot experiments were conducted to assess the biocontrol potential and impact of endophytes on the output, curcumin levels, and antioxidant activities of turmeric (Curcuma longa L.). The results showed that endophytes could control some disease-causing plant pathogens: 52% of all isolates have an antagonistic action against Fusarium oxysporum, 43% against Pythium myriotylum, 35% against Phytophthora megakarya, and 56% against Ralstonia solanacearum in vitro. Eight months after sowing, most endophyte isolates can increase the yield of turmeric rhizomes on a sterile substrate after inoculation, with yields ranging from 42 to 105% higher than the control and 3 to 50% higher than the urea treatment. In addition, 52% endophytes isolate significantly raised curcumin levels after 8 months of culture (from 2.1 to 3.1%) compared to control (1.7%) and urea treatment (1.8%). These endophytes promote an increase in the levels of reduced glutathione (22%), total thiols (26%), and carotenoids (91%) in turmeric. The study concludes that, in general, the endophytes-turmeric association can stimulate turmeric rhizome production, curcumin, and the antioxidant activities of the plant. They can also be used as biocontrol agents for plant pathogens.

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.

Effects of Dark Septate Endophytes on the Performance and Soil Microbia of Lycium ruthenicum Under Drought Stress

In the current study, we explored the effects of dark septate endophytes (DSE) (Neocamarosporium phragmitis, Alternaria chlamydospore, and Microascus alveolaris) on the performance and rhizosphere soil microbial composition of Lycium ruthenicum Murr under drought stress. Differences in plant growth and physiological indexes, soil parameters, and microbial composition under different treatments were studied. Three DSE species could form good symbiotic relationships with L. ruthenicum plants, and the symbionts depended on DSE species and water availability. Inoculation of DSE had the greatest benefit on host plants under drought conditions. In particular, N. phragmitis and A. chlamydospore had a significant positive influence on the biomass, morphological and physiological indexes of host plants. Additionally, the content of arbuscular mycorrhiza (AM) fungi, gram-negative bacteria, and actinomycetes in the soil was significantly elevated after DSE inoculation in the absence of water. Based on a variance decomposition analysis, DSE was the most important factor affecting the growth and physiological parameters of host plants, and DSE inoculation combined with water conditions significantly affected the contents of soil microbial communities. Structural equation model (SEM) analysis showed that the positive effects of DSE on L. ruthenicum varied with DSE species and plant parameters under different water conditions. These results are helpful to understand the ecological function of DSE and its potential application in the cultivation of L. ruthenicum plants in drylands.

Application of Cerium Dioxide Nanoparticles and Chromium-Resistant Bacteria Reduced Chromium Toxicity in Sunflower Plants

The continuous increase in the heavy metals concentration in the soil due to anthropogenic activities has become a global issue. The chromium, especially hexavalent chromium, is highly toxic for living organisms due to high mobility, solubility, and carcinogenic properties. Considering the beneficial role of nanoparticles and bacteria in alleviating the metal stress in plants, a study was carried out to evaluate the role of cerium dioxide (CeO₂) nanoparticles (NPs) and Staphylococcus aureus in alleviating the chromium toxicity in sunflower plants. Sunflower plants grown in chromium (Cr) contaminated soil (0, 25, and 50 mg kg^-1) were treated with CeO₂ nanoparticles (0, 25, and 50 mg L^-1) and S. aureus. The application of Cerium Dioxide Nanoparticles (CeO₂ NPs) significantly improved plant growth and biomass production, reduced oxidative stress, and enhanced the enzymatic activities in the sunflower plant grown under chromium stress. The application of S. aureus further enhanced the beneficial role of nanoparticles in alleviating metal-induced toxicity. The maximum improvement was noted in plants treated with both nanoparticles and S. aureus. The augmented application of CeO₂ NPs (50 mg l^-1) at Cr 50 mg kg^-1 increased the chl a contents from 1.2 to 2.0, chl b contents 0.5 to 0.8 and mg g^-1 FW, and decreased the leakage of the electrolyte from 121 to 104%. The findings proved that the application of CeO₂ nanoparticles and S. aureus could significantly ameliorate the metal-induced stress in sunflower plants. The findings from this study can provide new horizons for research in the application of nanoparticles in phytoremediation and bioremediation.

Amelioration of Chromium-Induced Oxidative Stress by Combined Treatment of Selected Plant-Growth-Promoting Rhizobacteria and Earthworms via Modulating the Expression of Genes Related to Reactive Oxygen Species Metabolism in Brassica juncea

Chromium (Cr) toxicity leads to the enhanced production of reactive oxygen species (ROS), which are extremely toxic to the plant and must be minimized to protect the plant from oxidative stress. The potential of plant-growth-promoting rhizobacteria (PGPR) and earthworms in plant growth and development has been extensively studied. The present study was aimed at investigating the effect of two PGPR (Pseudomonas aeruginosa and Burkholderia gladioli) along with earthworms (Eisenia fetida) on the antioxidant defense system in Brassica juncea seedlings under Cr stress. The Cr toxicity reduced the fresh and dry weights of seedlings, enhanced the levels of superoxide anion (O₂•^-), hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and electrolyte leakage (EL), which lead to membrane as well as the nuclear damage and reduced cellular viability in B. juncea seedlings. The activities of the antioxidant enzymes, viz., superoxide dismutase (SOD), guaiacol peroxidase (POD), ascorbate peroxidase (APOX), glutathione peroxidase (GPOX), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) were increased; however, a reduction was observed in the activity of catalase (CAT) in the seedlings under Cr stress. Inoculation of the PGPR and the addition of earthworms enhanced the activities of all other antioxidant enzymes except GPOX, in which a reduction of the activity was observed. For total lipid- and water-soluble antioxidants and the non-enzymatic antioxidants, viz., ascorbic acid and glutathione, an enhance accumulation was observed upon the inoculation with PGPR and earthworms. The supplementation of PGPR with earthworms (combined treatment) reduced both the reactive oxygen species (ROS) and the MDA content by modulating the defense system of the plant. The histochemical studies also corroborated that the combined application of PGPR and earthworms reduced O₂•^-, H₂O₂, lipid peroxidation, and membrane and nuclear damage and improved cell viability. The expression of key antioxidant enzyme genes, viz., SOD, CAT, POD, APOX, GR, DHAR, and GST showed the upregulation of these genes at post-transcriptional level upon the combined treatment of the PGPR and earthworms, thereby corresponding to the improved plant biomass. However, a reduced expression of RBOH1 gene was noticed in seedlings supplemented under the effect of PGPR and earthworms grown under Cr stress. The results provided sufficient evidence regarding the role of PGPR and earthworms in the amelioration of Cr-induced oxidative stress in B. juncea.

Production of indole-3-acetic acid by Bacillus circulans E9 in a low-cost medium in a bioreactor

Bacillus circulans E9 (now known as Niallia circulans) promotes plant growth-producing indole-3-acetic acid (IAA), showing potential for use as a biofertilizer. In this work, the use of a low-cost medium containing industrial substrates, soybean, pea flour, Solulys, Pharmamedia, yeast extract, and sodium chloride (NaCl), was evaluated as a substitute for microbiological Luria Broth (LB) medium for the growth of B. circulans E9 and the production of IAA. In Erlenmeyer flasks with pea fluor medium (PYM), the maximum production of IAA was 7.81 ± 0.16 μg mL^-1, while in microbiological LB medium, it was 3.73 ± 0.15 μg mL^-1. In addition, an oxygen transfer rate (OTR) of 1.04 kg O₂ m^-3 d^-1 allowed the highest bacterial growth (19.3 ± 2.18 × 10¹⁰ CFU mL^-1) and IAA production (10.7 μg mL^-1). Consequently, the OTR value from the flask experiments was used to define the conditions for the operation of a 1 L stirred tank bioreactor. The growth and IAA production of B. circulans cultured in a bioreactor with PYM medium were higher (8 and 1.6 times, respectively) than those of bacteria cultured in Erlenmeyer flasks. IAA produced in a bioreactor by B. circulans was shown to induce the root system in Arabidopsis thaliana, similar to synthetic IAA. The results of this study demonstrate that PYM medium may be able to be used for the mass production of B. circulans E9 in bioreactors, increasing both bacterial growth and IAA production. This low-cost medium has the potential to be employed to grow other IAA-producing bacterial species.

Cadmium Stabilization and Redox Transformation Mechanism in Maize Using Nanoscale Zerovalent-Iron-Enriched Biochar in Cadmium-Contaminated Soil

Cadmium (Cd) is a readily available metal in the soil matrix, which obnoxiously affects plants and microbiota; thus, its removal has become a global concern. For this purpose, a multifunctional nanoscale zerovalent-iron enriched biochar (nZVI/BC) was used to alleviate the Cd-toxicity in maize. Results revealed that the nZVI/BC application significantly enhanced the plant growth (57%), chlorophyll contents (65%), intracellular permeability (61%), and biomass production index (76%) by restraining Cd uptake relative to Cd control. A Cd stabilization mechanism was proposed, suggesting that high dispersion of organic functional groups (C-O, C-N, Fe-O) over the surface of nZVI/BC might induce complex formations with cadmium by the ion exchange process. Besides this, the regular distribution and deep insertion of Fe particles in nZVI/BC prevent self-oxidation and over-accumulation of free radicals, which regulate the redox transformation by alleviating Cd/Fe+ translations in the plant. Current findings have exposed the diverse functions of nanoscale zerovalent-iron-enriched biochar on plant health and suggest that nZVI/BC is a competent material, feasible to control Cd hazards and improve crop growth and productivity in Cd-contaminated soil.

Bioremediation of potentially toxic elements of sewage sludge using sunflower (Heliantus annus L.) in greenhouse and field conditions

The bioremediation of sewage sludge, containing potentially toxic elements (heavy metals), by the hyperaccumulator sunflower (Helianthus annus L.), was determined in greenhouse (G) and field (F) conditions in Isfahan, Iran. The soil pots, mixed with dried sewage sludge at 0, 15, 30, 45, and 60 mg/kg, were planted with sunflower seedlings and kept in the greenhouse (G) and in the field (F). Different soil physicochemical and plant biochemical properties including heavy metal uptake of nickel (Ni), chromium (Cr), lead (Pb), and cadmium (Cd) were determined. In contrast with the soil pH, soil salinity, organic matter, nitrogen, and not soil CaCO₃, were significantly enhanced by increasing sewage sludge. Sewage sludge was significant on plant uptake of Ni (2.27-4.25 mg/kg), Cr (3.27-4.75 mg/kg), Cd (13.85-15.27 mg/kg), and total chlorophyll (1.69-1.99 mg/g) in the greenhouse, and plant uptake of Ni (1.75-2.75 mg/kg) and Cd (1.37-2.25 mg/kg), and chlorophyll b (0.06-0.26 mg/g), total chlorophyll (0.57-1.16 mg/g), and carotenoids (1.10-1.61 mg/g) in the field. Although Pb was not significantly affected by sewage sludge, it showed the highest bioaccumulation factor of 0.96 at 15 mg/kg. Interestingly, the heavy metals were all positively and significantly correlated with each other and with plant carotenoids, similar to the positive and significant correlations between Pb with chlorophyll a and b. Accordingly, the increased levels of carotenoids, acting as antioxidant, may be an indicator of oxidative stress. Sunflower plants can be used as an efficient method for the bioremediation of the soils polluted with sewage sludge including Ni, Cr, and Cd.

Lead contamination of soils, sediments, and vegetation in a shooting range and adjacent terrestrial and aquatic ecosystems: A holistic approach for evaluating potential risks

It is well accepted that shooting ranges constitute hotspots of Pb contamination. This study evaluated the degree of Pb contamination of soils, sediments and vegetation within the boundaries of a highly visited shooting range, as well as the fluvial transport and dispersal of Pb, and therefore the contamination of adjacent river and water reservoir. Soils in the shooting range were severely contaminated with Pb, as indicated by the values of enrichment and contamination factor. The concentration of Pb in these soils ranged from 791 mg kg^-1 to 7265 mg kg^-1, being several dozens or even hundreds of times higher compared with control background samples. A temporary stream being in close proximity was also polluted, though to a much lesser extent. The degree of Pb contamination was negatively correlated with the distance from the shooting range. To this effect, the degree of contamination of the river and the water reservoir being in the vicinity of the shooting range was negligible, as sediments and water samples preserved similar Pb concentrations with control samples. However, cultivated (olives) and wild native plant species grown in the area of the shooting range were found to uptake and accumulate high concentrations of Pb in their tissues (even 50 times higher compared with control samples). The severe contamination of soils, sediments and vegetation in the studied shooting range can provoke very high ecological risks. Overall, results suggest that management measures should be undertaken within the boundaries of the studied shooting range.

Experimental design of ligandless sonication-assisted liquid- phases microextraction based on hydrophobic deep eutectic solvents for accurate determination of Pb(II) and Cd(II) from waters and food samples at trace levels

A straightforward, accurate and efficient analytical procedure was developed by ligandless sonication-assisted liquid- phases microextraction based on hydrophobic deep eutectic solvents (SA-LPME-HDES) to trace toxic Pb(II) and Cd(II) in waters and foods. Optimization of the SA-LPME-HDES procedure was carried out by Box-Behnken design. Under optimum conditions, linear ranges for Pb(II) and Cd(II) were 0.8-350 (r²:0.9962) and 1.5-500 µg L^-1 (r²: 0.9937), respectively. Relative standard deviations (N = 5, 10 µg L^-1) were 1.4% for Pb(II) and 1.6% for Cd(II), respectively. Limits of detection were 0.24, and 0.46 µg L^-1, respectively. The accuracy was evaluated by the analysis of two certified reference materials and the results were to be in agreement with the certified values. The SA-LPME-HDES method was successfully applied to tap water, mineral water, river water, well-water, sesame, peanut, eggplant, corn, wheat, soy and cucumber. The SA-LPME-HDES method allows operational simplicity, green, and low cost when compared with some microextraction procedure.

Pseudomonas sp. TCd-1 significantly alters the rhizosphere bacterial community of rice in Cd contaminated paddy field

Cadmium (Cd) pollution of paddy soils is one of the main concerns causing food security and environmental problems. Microbial bioremediation is an effective and eco-friendly measure that uses microbes to reduce Cd accumulation in crops. Additionally, rhizosphere bacterial communities also act essential roles in crop tolerance of heavy metals. However, the effects of inoculations with Cd resistant bacteria on crop rhizosphere bacterial communities under Cd exposure are largely unknown. In this study, we used high-throughput 16S rRNA gene sequencing technologies to explore the community structure and co-occurrence network of the rhizosphere bacterial communities associated with the rice crop under different Cd treatments and the application of Cd-tolerant strain Pseudomonas sp. TCd-1. We found that the strain TCd-1 both significantly reduced the rhizobacterial alpha diversity and changed the beta diversity. PERMANOVA and NMDS analysis showed that Cd stress and TCd-1 strain could act as strong environmental filters resulting in observable differentiation of rhizobacterial community composition among different groups. In addition, RDA results indicated that the rhizosphere pH, root Cd content, catalase (CAT), urease (URE), gibberellic acid (GA3) exert significant association with rhizosphere bacterial assembly. PICRUSt analysis revealed that the TCd-1 strain improved the metabolic capacity of rhizosphere bacteria under Cd stress. Furthermore, co-occurrence network topological features and keystone taxa also varied among different groups. This study could provide necessary insights into developing an efficient bioremediation and safe production of rice crops in Cd contaminated paddy fields with the application of Pseudomonas sp. TCd-1 strain, as well as advance our understanding of the principles of rhizosphere bacterial community assembly under Cd stress.

Bacterial Endophytes as a Promising Approach to Enhance the Growth and Accumulation of Bioactive Metabolites of Three Species of Chenopodium Sprouts

Sprouts are regarded as an untapped source of bioactive components that display various biological properties. Endophytic bacterium inoculation can enhance plant chemical composition and improve its nutritional quality. Herein, six endophytes (Endo 1 to Endo 6) were isolated from Chenopodium plants and morphologically and biochemically identified. Then, the most active isolate Endo 2 (strain JSA11) was employed to enhance the growth and nutritive value of the sprouts of three Chenopodium species, i.e., C. ambrosoides, C. ficifolium, and C. botrys. Endo 2 (strain JSA11) induced photosynthesis and the mineral uptake, which can explain the high biomass accumulation. Endo 2 (strain JSA11) improved the nutritive values of the treated sprouts through bioactive metabolite (antioxidants, vitamins, unsaturated fatty acid, and essential amino acids) accumulation. These increases were correlated with increased amino acid levels and phenolic metabolism. Consequently, the antioxidant activity of the Endo 2 (strain JSA11)-treated Chenopodium sprouts was enhanced. Moreover, Endo 2 (strain JSA11) increased the antibacterial activity against several pathogenic bacteria and the anti-inflammatory activities as evidenced by the reduced activity of cyclooxygenase and lipoxygenase. Overall, the Endo 2 (strain JSA11) treatment is a successful technique to enhance the bioactive contents and biological properties of Chenopodium sprouts.

Dynamic study of the lead (Pb) tolerance and accumulation characteristics of new dwarf bamboo in Pb-contaminated soil

Dwarf bamboo is a woody plant with potential for use in the remediation of Pb-contaminated soil. Due to its clonal growth habit, there are two keys to its application for continuous soil Pb remediation: 1) its ability to form shoots and grow into new bamboo normally under Pb stress and 2) the Pb tolerance and accumulation characteristics of this new bamboo. Here, 5 species of dwarf bamboo were treated with 2 levels of soil Pb stress (0 and 1500 mg kg^-1). In the roots of 3 of the species (Sasa argenteostriata, Sasaella glabra, and Indocalamus decorus), Pb tended to be distributed along the cell wall and transported to vacuoles. In the other 2 species (Sasa auricoma and Sasa fortunei), Pb was arranged linearly along the cell wall. Under Pb treatment, the new bamboo of all species showed gradual physiological adaptation to Pb stress. Correlations of the net photosynthetic rate, superoxide dismutase activity, and free proline levels with Pb content in new leaves in November were all higher than those in July, though that of malondialdehyde content decreased, suggesting that new dwarf bamboo exhibits good soil Pb stress tolerance. Sasa argenteostriata and Indocalamus decorus consistently maintained higher antioxidant enzyme activities and free proline levels than the other species under Pb treatment, and the total biomass per pot of the new bamboo decreased the least compared to that in the Pb-free treatment for these two species. Therefore, these bamboo species may be used in the long-term continuous remediation of Pb-contaminated soil.

Physiological responses and health risks of edible amaranth under simultaneous stresses of lead from soils and atmosphere

Lead (Pb) is widely distributed in the environment that can impose potential risks to vegetables and humans. In this work, we conducted a pot experiment in Southern China to examine the physiological response and risk of edible amaranth (Amaranthus tricolor L.) under the simultaneous stresses of lead from soil and atmosphere. The results indicate that the lead content of amaranth substantially exceeded China's national standard when Pb concentration from soils and atmosphere was high, and comparing to teenagers and adults, children exposed a higher health risk after consuming the contaminated amaranth. Under the co-stress, the lead in roots of amaranth mainly came from the soil, but the Pb from atmospheric deposition can significantly affect the lead concentration in leaves. While lead from atmospheric deposition is found to promote the growth of amaranth, the stress of lead from the soils shows an inhibitory effect, as indicated by the increase in H₂O₂ content, the damage in cell membranes, and the limitation in chlorophyll synthesis. The antioxidant system in stems and leaves of amaranth can effectively alleviate the Pb toxicity. However, the stress of high lead concentration from soils can substantially suppress the antioxidant enzyme activity of roots. While it is found that heavy metals in soils can significantly affect the vegetables grown in a multi-source pollution environment, we also call for the attention on the potential health risk imposed by the lead from atmospheric deposition. This study provides an important reference for the prevention and control of crop contamination in multi-source pollution environments.

Alleviating lead-induced phytotoxicity and enhancing the phytoremediation of castor bean (Ricinus communis L.) by glutathione application: new insights into the mechanisms regulating antioxidants, gas exchange and lead uptake

Heavy metals pollution represents a serious issue for cultivable lands and ultimately threatens the worldwide food security. Lead (Pb) is a menacing metal which induces toxicity in plants and humans. Lead toxicity reduces the photosynthesis in plants, resulting in the reduction of plant growth and biomass. The excessive concentration of Pb in soil accumulates in plants body and enters into food chain, resulting in health hazards in humans. The phytoremediation is eco-friendly and cost-efficient technique to clean up the polluted soils. However, to the best of our Knowledge, there are very few reports addressing the enhancement of the phytoremediation potential of castor bean plants. Therefore, the present study aimed to investigate the potential role of glutathione (GSH), as a promising plant growth regulator, in enhancing the lead stress tolerance and phytoremediation potential of castor bean plants grown under lead stress conditions. The results indicated that Pb stress reduced the growth, biomass, chlorophyll pigments and gas exchange attributes of castor bean plants, causing oxidative damage in plants. Pb stress induced the oxidative stress markers and activities of antioxidant enzymes. On the other hand, the application of GSH reduced oxidative stress markers, but enhanced the growth, biomass, photosynthetic pigments, gas exchange attributes, Pb accumulation and antioxidant enzymes activities of lead-stressed castor bean plants. Both Pb uptake and Pb accumulation were increased by increasing concentrations of Pb in a dose-additive manner. However, at high dose of exogenous GSH (25 mg L-1) further enhancements were recorded in the Pb uptake in shoot by 48% and in root by 46%; Pb accumulation was further enhanced in shoot by 98% and in root by 101% in comparison with the respective control where no GSH was applied. Taken together, the findings revealed the promising role of GSH in enhancing the lead stress tolerance and phytoremediation potential of castor bean (Ricinus communis) plants cultivated in Pb-polluted soils through regulating leaf gas exchange, antioxidants machinery, and metal uptake.

Compost mixed fruits and vegetable waste biochar with ACC deaminase rhizobacteria can minimize lead stress in mint plants

High lead (Pb) concentration in soils is becoming a severe threat to human health. It also deteriorates plants, growth, yield and quality of food. Although the use of plant growth-promoting rhizobacteria (PGPR), biochar and compost can be effective environment-friendly amendments for decreasing Pb stress in crop plants, the impacts of their simultaneous co-application has not been well documented. Thus current study was carried, was conducted to investigate the role of rhizobacteria and compost mixed biochar (CB) under Pb stress on selected soil properties and agronomic parameters in mint (Mentha piperita L.) plants. To this end, six treatments were studied: Alcaligenes faecalis, Bacillus amyloliquefaciens, CB, PGPR1 + CB, PGPR2 + CB and control. Results showed that the application A. faecalis + CB significantly decreased soil pH and EC over control. However, OM, nitrogen, phosphorus and potassium concentration were significantly improved in the soil where A. faecalis + CB was applied over control. The A. faecalis + CB treatment significantly improved mint plant root dry weight (58%), leaves dry weight (32%), chlorophyll (37%), and N (46%), P (39%) and K (63%) leave concentration, while also decreasing the leaves Pb uptake by 13.5% when compared to the unamended control. In conclusion, A. faecalis + CB has a greater potential to improve overall soil quality, fertility and mint plant productivity under high Pb soil concentration compared to the sole application of CB and A. faecalis.

Bacterial tolerance strategies against lead toxicity and their relevance in bioremediation application

Among heavy metals, lead (Pb) is a non-essential metal having a higher toxicity and without any crucial known biological functions. Being widespread, non-biodegradable and persistent in every sphere of soil, air and water, Pb is responsible for severe health and environmental issues, which need appropriate remediation measures. However, microbes inhabiting Pb-contaminated area are found to have evolved distinctive mechanisms to successfully thrive in the Pb-contaminated environment without exhibiting any negative effects on their growth and metabolism. The defensive strategies used by bacteria to ameliorate the toxic effects of lead comprise biosorption, efflux, production of metal chelators like siderophores and metallothioneins and synthesis of exopolysaccharides, extracellular sequestration and intracellular bioaccumulation. Lead remediation technologies by employing microbes may appear as potential advantageous alternatives to the conventional physical and chemical means due to specificity, suitability for applying in situ condition and feasibility to upgrade by genetic engineering. Developing strategies by designing transgenic bacterial strain having specific metal binding properties and metal chelating proteins or higher metal adsorption ability and using bacterial activity such as incorporating plant growth-promoting rhizobacteria for improved Pb resistance, exopolysaccharide and siderophores and metallothionein-mediated immobilization may prove highly effective for formulating bioremediation vis-a-vis phytoremediation strategies.

Synergistic effect of organo-mineral amendments and plant growth-promoting rhizobacteria (PGPR) on the establishment of vegetation cover and amelioration of mine tailings

Mine tailings pose a huge hazard for environmental and human health, and the establishment of vegetation cover is crucial to reduce pollutant dispersion for the surroundings. However, their hostile physicochemical conditions hamper plant growth, compromising phytoremediation strategies. This study aims to investigate the role of organo-mineral amendments and plant growth-promoting rhizobacteria (PGPR) on the improvement of mine tailings properties and Lolium perenne L. (ryegrass) growth. Plants were grown in mine tailings mixed with an agricultural soil (1:1), 10% compost, and supplied with two different inorganic amendments - rock phosphate (6%) or lime (3%), and inoculated with the rhizobacterial strains Advenellakashmirensis BKM20 (B1) and Mesorhizobium tamadayense BKM04 (B2). The application of organo-mineral amendments ameliorated tailings characteristics, which fostered plant growth and further enhanced soil fertility and microbial activity. These findings were consistent with the increase of total organic carbon levels, with the higher numbers of heterotrophic and phosphate solubilizing bacteria, and higher dehydrogenase and urease activities, found in these substrates after plant establishment. Plant growth was further boosted by PGPR inoculation, most noticeable by co-inoculation of both strains. Moreover, inoculated plants showed increased activities for several antioxidant enzymes (catalase, peroxidase, polyphenoloxidase, and glutathione reductase) which indicate a reinforced antioxidant system. The application of agricultural soil, compost and lime associated with the inoculation of a mixture of PGPR proved to enhance the establishment of vegetation cover, thus promoting the stabilization of Kettara mine tailings. Nonetheless, further studies are needed in order to confirm its effectiveness under field conditions.

Selenium Supplementation and Crop Plant Tolerance to Metal/Metalloid Toxicity

Selenium (Se) supplementation can restrict metal uptake by roots and translocation to shoots, which is one of the vital stress tolerance mechanisms. Selenium can also enhance cellular functions like membrane stability, mineral nutrition homeostasis, antioxidant response, photosynthesis, and thus improve plant growth and development under metal/metalloid stress. Metal/metalloid toxicity decreases crop productivity and uptake of metal/metalloid through food chain causes health hazards. Selenium has been recognized as an element essential for the functioning of the human physiology and is a beneficial element for plants. Low concentrations of Se can mitigate metal/metalloid toxicity in plants and improve tolerance in various ways. Selenium stimulates the biosynthesis of hormones for remodeling the root architecture that decreases metal uptake. Growth enhancing function of Se has been reported in a number of studies, which is the outcome of improvement of various physiological features. Photosynthesis has been improved by Se supplementation under metal/metalloid stress due to the prevention of pigment destruction, sustained enzymatic activity, improved stomatal function, and photosystem activity. By modulating the antioxidant defense system Se mitigates oxidative stress. Selenium improves the yield and quality of plants. However, excessive concentration of Se exerts toxic effects on plants. This review presents the role of Se for improving plant tolerance to metal/metalloid stress.

Role of plant growth promoting rhizobacteria in the alleviation of lead toxicity to Pisum sativum L

Plant-microbe interaction is a significant tool to tackle heavy metals problem in the soil. A pot trial was conducted to evaluate the efficiency of lead tolerant rhizobacteria in improving pea growth under Pb stress. Lead sulfate (PbSO4) was used for spiking (250, 500, and 750 mg kg-1). Results indicated that inoculation with Pb-tolerant PGPR strain not only alleviated the harmful impacts of Pb on plant growth but also immobilized it in the soil. PGPR in the presence of Pb at concentrations of 0, 250, 500 and 750 mg kg-1, increased shoot and root lengths by 21, 15, 18% and 72, 80, 84%, respectively, than uninoculated control. Moreover, fresh biomass of shoots and roots were also increased by 51, 45, 35% and 57, 101, 139% respectively, at Pb concentrations of 250, 500 and 750 mg kg-1. In addition, PGPR inoculation also reduced Pb concentration in the roots and shoots by 57, 55, 49% and 70, 56 and 58% respectively, than uninoculated control. So, PGPR proved to be an efficient option for reducing Pb mobility and can be effectively used for its phytostabilization. Novelty statementLead (Pb) is highly noxious and second most toxic element in the nature having high persistence. It ranks 1st in the priority list of hazardous substances and causes adverse effects after its entry into the living system. So, its remediation is inevitable. Plant growth promoting rhizobacteria (PGPR) possess the potential to not only survive under stressed environments, but also promote plant growth on account of their different plant growth promoting mechanisms.Most researchers have worked on its bioaccumulation in plant body. This study however, used pea as a test crop and caused Pb phytostabilization and thereby, suppressed its entry in the above-ground plant parts.

Deciphering lead tolerance mechanisms in a population of the plant species Biscutella auriculata L. from a mining area: Accumulation strategies and antioxidant defenses

The uptake and distribution of Pb and the mechanisms involved in the metal tolerance have been investigated in a mine population of Biscutella auriculata. Seedlings were exposed to 125 μM Pb(NO₃)₂ for 15 days under semihydroponic conditions. The results showed an increase in the size of Pb-treated seedlings and symptoms of toxicity were not observed. ICP-OES analyses showed that Pb accumulation was restricted to root tissue. Imaging of Pb accumulation by dithizone histochemistry revealed the presence of the metal in vacuoles and cell wall in root cells. The accumulation of Pb in vacuoles could be stimulated by an increase in phytochelatin PC2 content. Pb did not promote oxidative damage and this is probably due the increase of antioxidative defenses. In the leaves, Pb produced a significant increase in superoxide dismutase activity, while in roots an increase in catalase and components of the Foyer- Halliwell-Asada cycle were observed. The results indicated that Biscutella auriculata has a high capacity to tolerate Pb and this is mainly due to a very efficient mechanism to sequester the metal in roots and a capacity to avoid oxidative stress. This species could therefore be very useful for phytostabilization and repopulation of areas contaminated with Pb.

Phytosociology and antioxidant profile study for selecting potent herbs for phytoremediation of crude oil-contaminated soils

Crude oil exploration activities affect the surrounding vegetation. The present investigation deals with the study of phytosociology and biochemical profiles of the herbaceous community in the active and abandoned oil drilling sites of crude oil-explored area. For comparison, a similar investigation was also carried out in control sites where oil exploration activities were not evident. At first, a phytosociological investigation was carried out and based on the results obtained antioxidant enzyme profiles of dominant herbs were studied to understand their defense mechanism to crude oil-associated stress. A total of 69 plant species belonging to 20 families were recorded in the studied sites and the family Cyperaceae was the most dominant in the crude oil-contaminated sites. The results revealed that the plants growing near the oil-explored-contaminated sites exhibit a higher level of DPPH and H₂O₂ radical scavenging activities as compared to control plant samples. For DPPH assay, the lowest IC₅₀ value was exhibited by Cyperus rotundus which was recorded to be 31.49 and 55.31 respectively for the samples of contaminated and control sites. Again, in the case of H₂O₂ scavenging activity assay, Parthenium hysterophorus showed the lowest IC₅₀ values of 27.48 and 63.07 for the samples of contaminated and control sites respectively. As a whole, the findings confirm the superior defense mechanism of some dominant herbs of the contaminated sites that include Torenia flava, Croton bonplandianus, Eclipta alba, Cyperus rotundus, Cyperus brevifolius, and Parthenium hysterophorus and their suitability for use in phytomanagement practices.

Unravelling the Role of Rhizospheric Plant-Microbe Synergy in Phytoremediation: A Genomic Perspective

Background

Accretion of organic and inorganic contaminants in soil interferes in the food chain, thereby posing a serious threat to the ecosystem and adversely affecting crop productivity and human life. Both endophytic and rhizospheric microbial communities are responsible for the biodegradation of toxic organic compounds and have the capability to enhance the uptake of heavy metals by plants via phytoremediation approaches. The diverse set of metabolic genes encoding for the production of biosurfactants and biofilms, specific enzymes for degrading plant polymers, modification of cell surface hydrophobicity and various detoxification pathways for the organic pollutants, plays a significant role in bacterial driven bioremediation. Various genetic engineering approaches have been demonstrated to modulate the activity of specific microbial species in order to enhance their detoxification potential. Certain rhizospheric bacterial communities are genetically modified to produce specific enzymes that play a role in degrading toxic pollutants. Few studies suggest that the overexpression of extracellular enzymes secreted by plant, fungi or rhizospheric microbes can improve the degradation of specific organic pollutants in the soil. Plants and microbes dwell synergistically, where microbes draw benefit by nutrient acquisition from root exudates whereas they assist in plant growth and survival by producing certain plant growth promoting metabolites, nitrogen fixation, phosphate solubilization, auxin production, siderophore production, and inhibition or suppression of plant pathogens. Thus, the plant-microbe interaction establishes the foundation of the soil nutrient cycle as well as decreases soil toxicity by the removal of harmful pollutants.

Conclusion

The perspective of integrating genetic approach with bioremediation is crucial to evaluate connexions among microbial communities, plant communities and ecosystem processes with a focus on improving phytoremediation of contaminated sites.

Potential role of compost mixed biochar with rhizobacteria in mitigating lead toxicity in spinach

Consumption of heavy metals, especially lead (Pb) contaminated food is a serious threat to human health. Higher Pb uptake by the plant affects the quality, growth and yield of crops. However, inoculation of plant growth-promoting rhizobacteria (PGPR) along with a mixture of organic amendments and biochar could be an effective way to overcome the problem of Pb toxicity. That’s why current pot experiment was conducted to investigate the effect of compost mixed biochar (CB) and ACC deaminase producing PGPR on growth and yield of spinach plants under artificially induced Pb toxicity. Six different treatments i.e., control, Alcaligenes faecalis (PGPR1), Bacillus amyloliquefaciens (PGPR2), compost + biochar (CB), PGPR1 + CB and PGPR2 + CB were applied under 250 mg Pb kg^-1 soil. Results showed that inoculation of PGPRs (Alcaligenes faecalis and Bacillus amyloliquefaciens) alone and along with CB significantly enhanced root fresh (47%) and dry weight (31%), potassium concentration (11%) in the spinach plant. Whereas, CB + Bacillus amyloliquefaciens significantly decreased (43%) the concentration of Pb in the spinach root over control. In conclusion, CB + Bacillus amyloliquefaciens has the potential to mitigate the Pb induced toxicity in the spinach. The obtained result can be further used in the planning and execution of rhizobacteria and compost mixed biochar-based soil amendment.

Characterisation of early responses in lead accumulation and localization of Salix babylonica L. roots

BACKGROUND

Lead (Pb) is a harmful pollutant that disrupts normal functions from the cell to organ levels. Salix babylonica is characterized by high biomass productivity, high transpiration rates, and species specific Pb. Better understanding the accumulating and transporting Pb capability in shoots and roots of S. babylonica, the toxic effects of Pb and the subcellular distribution of Pb is very important.

RESULTS

Pb exerted inhibitory effects on the roots and shoots growth at all Pb concentrations. According to the results utilizing inductively coupled plasma atomic emission spectrometry (ICP-AES), S. babylonica can be considered as a plant with great phytoextraction potentials as translocation factor (TF) value > 1 is observed in all treatment groups throughout the experiment. The Leadmium™ Green AM dye test results indicated that Pb ions initially entered elongation zone cells and accumulated in this area. Then, ions were gradually accumulated in the meristem zone. After 24 h of Pb exposure, Pb accumulated in the meristem zone. The scanning electron microscopy (SEM) and energy-dispersive X-ray analyses (EDXA) results confirmed the fluorescent probe observations and indicated that Pb was localized to the cell wall and cytoplasm. In transverse sections of the mature zone, Pb levels in the cell wall and cytoplasm of epidermal cells was the lowest compared to cortical and vessel cells, and an increasing trend in Pb content was detected in cortical cells from the epidermis to vascular cylinder. Similar results were shown in the Pb content in the cell wall and cytoplasm of the transverse sections of the meristem. Cell damage in the roots exposed to Pb was detected by propidium iodide (PI) staining, which was in agreement with the findings of Pb absorption in different zones of S. babylonica roots under Pb stress.

CONCLUSION

S. babylonica L. is observed as a plant with great potential of Pb-accumulation and Pb-tolerance. The information obtained here of Pb accumulation and localization in S. babylonica roots can furthers our understanding of Pb-induced toxicity and its tolerance mechanisms, which will provide valuable and scientific information to phytoremediation investigations of other woody plants under Pb stress.

Synergistic ameliorative effect of iron oxide nanoparticles and Bacillus subtilis S4 against arsenic toxicity in Cucurbita moschata: polyamines, antioxidants, and physiochemical studies

The present study was intended to assess the potential of iron oxide nanoparticles (IONPs) and Bacillus subtilis S4 in mitigation of arsenic (As) stress in Cucurbita moschata. Cucurbita moschata seedlings were subjected to As stress for 60 days. Reduced level of growth parameters including photosynthetic pigments, rate of photosynthesis and gas exchange characteristics was observed in seedlings subjected to As stress. However, IONPs and B. subtilis S4 improved growth attributes and proline contents in supplemented C. moschata seedlings. Bacillus subtilis S4 inoculated seedlings showed higher activity of peroxidase (POD) and superoxide dismutase (SOD) under As toxicity. Similarly, the co-application of IONPs and B. subtilis S4 further increased the activity of these antioxidative enzymes. The As stress alleviation in inoculated C. moschata seedlings is credited to reduced levels of hydrogen peroxide (H₂O₂), malondialdehyde (MDA) and electrolyte leakage (EL) in IONPs and B. subtilis S4-treated plants. Furthermore, synergism between plant growth promoting bacteria (PGPB) and IONPs enhanced the biosynthesis of stress mitigating polyamines including spermidine and putrescine in As-stressed seedlings. Current research reveals that synergistic application of IONPs and B. subtilis S4 is an effective sustainable and ecofriendly approach for alleviation of As stress in C. moschata seedlings.

Heavy metal-immobilizing bacteria increase the biomass and reduce the Cd and Pb uptake by pakchoi (Brassica chinensis L.) in heavy metal-contaminated soil

Microbial immobilization is a novel and environmentally friendly technology that uses microbes to reduce metal availability in soil and accumulation of heavy metals in plants. We used urea agar plates to isolate urease-producing bacteria from the rhizosphere soil of pakchoi in Cd- and Pb-contaminated farmland and investigated their effects on Cd and Pb accumulation in pakchoi and the underlying mechanisms. The results showed that two urease-producing bacteria, Bacillus megaterium N3 and Serratia liquefaciens H12, were identified by screening. They had higher ability to produce urease (57.5 ms cm^-1 min^-1 OD₆₀₀^-1 and 76.4 ms cm^-1 min^-1 OD₆₀₀^-1, respectively). The two strains allowed for the immobilization of Cd and Pb by extracellular adsorption, bioprecipitation, and increasing the pH (from 6.94 to 7.05-7.09), NH₄⁺ content (69.1%-127%), and NH₄⁺/NO₃^- ratio (from 1.37 to 1.67-2.11), thereby reducing the DTPA-extractable Cd (35.3%-58.8%) and Pb (37.8%-62.2%) contents in the pakchoi rhizosphere soils and the Cd (76.5%-79.7%) and Pb (76.3%-83.5%) contents in the leaves (edible tissue) of pakchoi. The strains were highly resistant to heavy metal toxicity; produced IAA, siderophores and abscisic acid; and increased the NH₄⁺/NO₃^- ratio, which might be related to the two strains protectiing pakchoi against the toxic effect of Cd and Pb and increasing pakchoi biomass. Thus, the results were supposed to strain resources and a theoretical basis for the remediation of Cd- and Pb-contaminated farmlands for the safe production of vegetables.

Screening of Heavy Metal-Immobilizing Bacteria and Its Effect on Reducing Cd2+ and Pb2+ Concentrations in Water Spinach (Ipomoea aquatic Forsk.)

Microbial immobilization is considered as a novel and environmentally friendly technology that uses microbes to reduce heavy metals accumulation in plants. To explore microbial resources which are useful in these applications, three water spinach rhizosphere soils polluted by different levels of heavy metals (heavy pollution (CQ), medium pollution (JZ), and relative clean (NF)) were collected. The community composition of heavy metal-immobilizing bacteria in rhizosphere soils and its effects on reducing the Cd²⁺ and Pb²⁺ concentrations in water spinach were evaluated. Four hundred strains were isolated from the CQ (belonging to 3 phyla and 14 genera), JZ (belonging to 4 phyla and 25 genera) and NF (belonged to 6 phyla and 34 genera) samples, respectively. In the CQ sample, 137 strains showed a strong ability to immobilize Cd²⁺ and Pb²⁺, giving Cd²⁺ and Pb²⁺ removal rates of greater than 80% in solution; Brevundimonas, Serratia, and Pseudoarthrobacter were the main genera. In total, 62 strains showed a strong ability to immobilize Cd²⁺ and Pb²⁺ in the JZ sample and Bacillus and Serratia were the main genera. A total of 22 strains showed a strong ability to immobilize Cd²⁺ and Pb²⁺ in the NF sample, and Bacillus was the main genus. Compared to the control, Enterobacter bugandensis CQ-7, Bacillus thuringensis CQ-33, and Klebsiella michiganensis CQ-169 significantly increased the dry weight (17.16-148%) of water spinach and reduced the contents of Cd²⁺ (59.78-72.41%) and Pb²⁺ (43.36-74.21%) in water spinach. Moreover, the soluble protein and Vc contents in the shoots of water spinach were also significantly increased (72.1-193%) in the presence of strains CQ-7, CQ-33 and CQ-169 compared to the control. In addition, the contents of Cd and Pb in the shoots of water spinach meet the standard for limit of Cd²⁺ and Pb²⁺ in vegetables in the presence of strains CQ-7, CQ-33 and CQ-169. Thus, the results provide strains as resources and a theoretical basis for the remediation of Cd- and Pb-contaminated farmlands for the safe production of vegetables.

Cadmium and lead mixtures are less toxic to the Chinese medicinal plant Ligusticum chuanxiong Hort. Than either metal alone

Agricultural production of Ligusticum chuanxiong Hort. is often affected by heavy metal pollution in soil, especially mixtures of cadmium (Cd) and lead (Pb). We assessed metal-induced phytotoxicity in L. chuanxiong by exposing the plants to soil treated with Cd, Pb, or Cd/Pb mixtures. A combined Cd/Pb treatment alleviated the inhibition in plant growth, photosynthesis, and secondary metabolite generation seen in single-metal exposures in three of the four combinations. Most combined Cd/Pb treatments resulted in preferential uptake of magnesium, copper, and nitrogen in underground plant parts and accumulation of phosphorus and calcium in aboveground plant parts, thereby leading to improvements in photosynthetic potential. Compared with single-metal exposures, combined Cd/Pb treatment significantly decreased the contents of Cd by 16.67%-40.12% and Pb by 10.68%-21.70% in the plant, respectively. At the subcellular level, the Pb presence increased the Cd percentage associated with cell wall from 64.79% to 67.93% in rhizomes and from 32.76% to 45.32% in leaves, while Cd reduced Pb contents by 9.36%-46.39% in the subcellular fractions. A combined Cd/Pb treatment decreased the contents of water- and ethanol-extractable metal forms and increased the contents of acetic acid- and hydrochloric acid-extractable forms. The lower toxic effects of the Cd/Pb mixture in L. chuanxiong were associated with photosynthetic potential, subcellular distribution, the chemical forms of Cd and Pb, and synthesis of secondary metabolites. These findings are useful for plant production strategies in soils contaminated by heavy metals.