Phytoremediation Of Heavy Metal Contaminated Soil Research Articles

Cadmium/zinc stresses and plant cultivation influenced soil microflora: a pot experiment conducted in field

It’s of great challenge to address for heavy metal-contaminated soil. Once the farmland is contaminated with heavy metals, the microbial ecology of the plant rhizosphere will change, which in turn impacts crop productivity and quality. However, few studies have explored the effects of heavy metals on plant rhizosphere microbes in farmland and the role that plant cultivation plays in such a phytoremediation practice. In this study, the impacts of comfrey (Symphytum officinale L.) cultivation and the stresses of cadmium/zinc (Cd/Zn) on rhizosphere soil microflora were examined. Microbial DNA was collected from soils to evaluate the prevalence of bacteria and fungi communities in rhizosphere soils. High-throughput 16 S rRNA sequencing was used to determine the diversity of the bacterial and fungal communities. The results showed that growing comfrey on polluted soils reduced the levels of Cd and Zn from the vertical profile. Both the comfrey growth and Cd/Zn stresses affected the community of rhizosphere microorganisms (bacteria or fungi). Additionally, the analysis of PCoA and NMDS indicated that the cultivation of comfrey significantly changed the bacterial composition and structure of unpolluted soil. Comfrey cultivation in polluted and unpolluted soils did not result in much variance in the fungi’s species composition, but the fungal compositions of the two-type soils were noticeably different. This work provided a better understanding of the impacts of Cd/Zn stresses and comfrey cultivation on rhizosphere microbial community, as well as new insight into phytoremediation of heavy metal-contaminated soils.

Phytotoxicity Assay of Cu, Pb and Zn on Launaea cornuta and Sporobolus jacquemontii Grown in Heavy Metal contaminated soil

In this paper, a phytotoxicity assay is used to assess the harmfulness and tolerance of L. cornuta and S. jacquemontii in phytoremediation of heavy metal-contaminated soils. The effects of Pb, Cu, and Zn concentrations in the soil on the number of leaves generated, root and shoot growth, and tolerance indices of the investigated plant species were analyzed. The experimental plants were grown in soil with 0, 100, 300, 600, 1500, 2000, 2500, and 3000 mg/kg dry soil weight (DW for Pb, Cu, and Zn). Sample preparation and laboratory analysis followed the standard methods. Data were analyzed with one-way analysis of variance (ANOVA) using GraphPad Instat 3.1 software. The growth mean of different treatments was compared using Duncan’s Multiple Range Test at p < 0.05. Plants grown in soil containing more than 300/kg DW metal contents exhibited a significant effect on the growth of the root and shoot. Concentrations lower than 300 did not show any significant effects. At 1500 mg/kgDW, the numbers and sizes of leaves decreased very significantly, while at 2000 mg/kgDW both plants failed to survive. The toxic effects of the metals on biomass production showed inhibition in the following trend: Zn>Cu>Pb. The results suggest that hyper accumulator plants can also be affected by metals in the soils on which they grow. Therefore, the application of L. cornuta and S. jacquemontii as phytoremediation plants at higher metal soil concentrations requires the application of soil amendments to minimize the toxicity effect of metal on the plants.

Screening of heavy metal-resistant rhizobial and non-rhizobial microflora isolated from Trifolium sp. growing in mining areas.

Plant growth-promoting rhizobacteria (PGPR) can promote plant growth and development with several beneficial effects, especially in challenging environmental conditions, such as the presence of toxic contaminants. In this study, 49 isolates obtained from Trifolium sp. nodules growing on a Pb/Zn mine site were characterized for PGP traits including siderophores production, phosphate solubilization, extracellular enzymes production, and antifungal activity. The isolates were also screened for their ability to grow at increasing concentrations of NaCl and heavy metals, including lead, zinc, cobalt, copper, nickel, cadmium, and chromium. The findings of our study indicated that isolates Cupriavidus paucula RSCup01-RSCup08, Providencia rettgeri RSPro01, Pseudomonas putida RSPs01, Pseudomonas thivervalensis RSPs03-RSPs09, and Acinetobacter beijerinckii RSAci01 showed several key traits crucial for promoting plant growth, thus demonstrating the greatest potential. Most isolates displayed resistance to salt and heavy metals. Notably, Staphylococcus xylosus RSSta01, Pseudomonas sp. RSPs02, Micrococcus yunnanensis RSMicc01, and Kocuria dechangensis RSKoc01 demonstrated a significant capacity to grow at salt concentrations ranging from 10 to 20%, and isolates including Cupravidus paucula RSCup01-RSCup08 exhibited resistance to high levels of heavy metals, up to 1300 mg/L Pb++, 1200 mg/L Zn++, 1000 mg/L Ni++, 1000 mg/L Cd++, 500 mg/L Cu++, 400 mg/L Co++, and 50 mg/L CrVI+. Additionally, the analysis revealed that metal-resistant genes pbrA, czcD, and nccA were exclusively detected in the Cupriavidus paucula RSCup01 strain. The results of this study provide insights into the potential of plant growth-promoting rhizobacteria strains that might be used as inoculants to improve phytoremediation in heavy metal-contaminated soils.

Physiological responses of low- and high-cadmium accumulating Robinia pseudoacacia-rhizobium symbioses to cadmium stress

The role of rhizobia in alleviating cadmium (Cd) stress in woody legumes is still unclear. Therefore, two types of black locust (Robinia pseudoacacia L.) with high and low Cd accumulation abilities were selected from 11 genotypes in China, and the effects of rhizobium (Mesorhizobium huakuii GP1T11) inoculation on the growth, CO2 and H2O gas exchange parameters, Cd accumulation, and the absorption of mineral elements of the high (SX) and low Cd-accumulator (HB) were compared. The results showed that rhizobium-inoculation significantly increased biomass, shoot Cd contents, Cd accumulation, root-to-shoot translocation factor (TF) and the absorption and accumulation of mineral elements in both SX and HB. Rhizobium-inoculation increased chlorophyll a and carotenoid contents, and the intercellular carbon dioxide concentrations in HB plants. Under Cd exposure, the high-accumulator SX exhibited a significant decrease in photosynthetic CO2 fixation (Pn) and an enhanced accumulation of Cd in leaves, but coped with Cd exposure by increasing chlorophyll synthesis, regulating stomatal aperture (Gs), controlling transpiration (Tr), and increasing the absorption and accumulation of mineral elements. In contrast, the low-accumulator HB was more sensitive to Cd exposure despite preferential accumulation of Cd in roots, with decreased chlorophyll and carotenoid contents, but significantly increased root biomass. Compared to the low-accumulator HB, non-inoculated Cd-exposed SX plants had higher chlorophyll contents, and rhizobium-inoculated Cd-exposed SX plants had higher Pn, Tr, and Gs as well as higher levels of P, K, Fe, Ca, Zn, and Cu. In conclusion, the high- and low-Cd-accumulator exhibited different physiological responses to Cd exposure. Overall, rhizobium-inoculation of black locust promoted the growth and heavy metal absorption, providing an effective strategy for the phytoremediation of heavy metal-contaminated soils by this woody legume.

Selenium Nanoparticles Mitigate Cadmium Stress in Tomato through Enhanced Accumulation and Transport of Sulfate/Selenite and Polyamines.

Accumulation of cadmium (Cd) ions in soil is an increasingly acute ecological problem in agriculture production. Selenium nanoparticles (SeNPs) can mediate Cd tolerance in plants; however, the underlying mechanisms remain unclear. Herein, we show that the foliar application of SeNPs improved the adaptive capacity of tomato plants to decrease Cd-induced damage. SeNPs induced more Cd in roots but not in shoots despite greater accumulation of selenium and sulfur in both tissues and high selenate influx. Additionally, SeNPs significantly increased thiol compounds, including glutathione, cysteine, and phytochelatins, contributing to enhanced Cd detoxification. Importantly, SeNPs induced the expression of sulfate transporters 1:3, S-adenosylmethionine 1 and polyamine transporter 3. Then, experiments with mutants of these genes showed that SeNP-reduced Cd stress largely relies on the levels and shoot-to-root transport of selenium/sulfur and polyamines. These findings highlight the potential of SeNPs to improve crop production and phytoremediation in heavy metal-contaminated soils.

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.

Potential of Purslane (Portulaca oleracea L.) in Phytoremediation: A Study on the Bioaccumulation and Bio-Transfer of Cadmium, Nickel, and Copper in Contaminated Soils

As industrial and agricultural activities intensify and technology rapidly advances, soil pollution has escalated to alarming levels. The increasing contamination of agricultural areas and the crops cultivated therein has emerged as a significant contemporary issue. Phytoremediation, the use of plants to remove pollutants, is a promising method for mitigating soil heavy metal contamination. &#x0D; This study investigates the bioaccumulation capacity of purslane (Portulaca oleracea L.), a potential phytoremediator, in soils artificially contaminated with cadmium (Cd), nickel (Ni), and copper (Cu). Purslane was cultivated under controlled conditions with varying doses of Cd, Ni, and Cu. After 55 days, the plants were harvested and analysed for heavy metal concentrations in their roots, stems, and leaves. Results demonstrated a direct correlation between environmental heavy metal concentration and plant heavy metal content, with the most significant accumulation occurring in the roots. Leaf chlorophyll content was adversely affected by increased Cd, Ni, and Cu applications. The highest Cu, Ni, and Cd contents were found in the roots at 140 mg kg-1 Cu, 80 mg kg-1 Ni, and 20 mg kg-1 Cd applications, respectively. The bio-transfer coefficient (BTC), a measure of heavy metal transport from the root region to the leaves, was calculated. The BTC values ranged from 0.84-1.09 for Cu, 0.39-0.84 for Ni, and &gt;1 for Cd at the Control and 5 mg Cd kg-1 treatments. &#x0D; These findings suggest that purslane has potential for phytoremediation of heavy metal-contaminated soils, although the bioaccumulation and bio-transfer of heavy metals are dependent on the specific metal and its concentration in the soil. The study also highlights the potential risks associated with the consumption of plants grown in heavy metal-contaminated soils, as heavy metals can accumulate in different plant tissues, potentially entering the food chain.

OsHIPP17 is involved in regulating the tolerance of rice to copper stress.

Heavy metal-associated isoprenylated plant proteins (HIPPs) play vital roles in metal absorption, transport and accumulation in plants. However, so far, only several plant HIPPs have been functionally analyzed. In this study, a novel HIPP member OsHIPP17, which was involved in the tolerance to copper (Cu) was functionally characterized. In this study, qRT-PCR, Yeast transgenic technology, Plant transgenic technology, ICP-MS and so on were used for research. OsHIPP17 protein was targeted to the nucleus. The Cu concentration reached 0.45 mg/g dry weight due to the overexpression of OsHIPP17 in yeast cells. Meanwhile, the overexpression of OsHIPP17 resulted in the compromised growth of Arabidopsis thaliana (Arabidopsis) under Cu stress. The root length of Oshipp17 mutant lines was also significantly reduced by 16.74- 24.36% under 25 mM Cu stress. The roots of Oshipp17 rice mutant showed increased Cu concentration by 7.25%-23.32%. Meanwhile, knockout of OsHIPP17 decreased the expression levels of OsATX1, OsZIP1, OsCOPT5 or OsHMA5, and increased the expression levels of OsCOPT1 or OsHMA4. Antioxidant enzyme activity was also reduced in rice due to the knockout of OsHIPP17. Moreover, the expression levels of cytokinin-related genes in plants under Cu stress were also affected by overexpression or knockout of OsHIPP17. These results implied that OsHIPP17 might play a role in plant Cu toxic response by affecting the expression of Cu transport genes or cytokinin-related genes. Simultaneously, our work may shed light on the underlying mechanism of how heavy metals affect the plant growth and provide a novel rice genetic source for phytoremediation of heavy metal-contaminated soil.

Comparative Evaluation of Tree Species for Phytoremediation of Heavy Metal-Contaminated Soil: Effects of Humic and Salicylic Acid Application

Comparative Evaluation of Tree Species for Phytoremediation of Heavy Metal-Contaminated Soil: Effects of Humic and Salicylic Acid Application

Feasibility study of the environmental and economic impact of phytoremediation of heavy metal-contaminated soil

Feasibility study of the environmental and economic impact of phytoremediation of heavy metal-contaminated soil

Effects of intercropping on safe agricultural production and phytoremediation of heavy metal-contaminated soils

Intercropping with hyperaccumulators is believed to be an important and efficient way to achieve simultaneous safe agricultural production and phytoremediation of polluted soils. However, some studies have suggested that this technique might facilitate the uptake of heavy metals by crops. To investigate the effects of intercropping on the heavy metal contents of plants and soil, data from 135 global studies were collected and analyzed by meta-analysis. The results showed that intercropping could significantly reduce the contents of heavy metals in the main plants and soils. Plant species was the main factor that affected plant and soil metal contents in the intercropping system, and the heavy metal content could be significantly reduced when members of the Poaceae and Crassulaceae were used as main plants or when legumes were used as intercropped plants. Among all the intercropped plants, the best one for removing heavy metals from the soil was a Crassulaceae hyperaccumulator. These results not only highlight the main factors affecting intercropping systems but also provide reliable reference information for the practice of safe agricultural production coupled with phytoremediation of heavy metal-contaminated farmland.

24-epibrassinolide improves cadmium tolerance and lateral root growth associated with regulating endogenous auxin and ethylene in Kentucky bluegrass

The application of phytohormones is a viable technique to increase the efficiency of phytoremediation in heavy metal-contaminated soils. The objective of this study was to determine how the application of 24-epibrassinolide (EBR), a brassinosteroid analog, could regulate root growth and tolerance to cadmium (Cd) stress in Kentucky bluegrass. As a result, the number of lateral root primordia and total root length in the Cd-treated seedlings decreased by 33.1 % and 56.5 %, respectively. After the application of EBR, Cd accumulation in roots and leaves, and the negative effect of Cd on root growth were reduced under Cd stress. Additionally, the expression of the brassinosteroid signaling gene PpBRI1 was significantly upregulated by exogenous EBR. Moreover, exogenous EBR upregulated the expression of genes encoding antioxidant enzymes and improved the activity of antioxidant enzymes, thereby reduced oxidative stress in roots. Finally, targeted hormonomics analysis highlighted the utility of the application of EBR to alleviate the effect of Cd on the reduction in auxin (IAA) content and the increase in ethylene (ACC) content. These were known to be associated with the upregulation in the expression of auxin biosynthesis gene PpYUCCA1 and downregulation in the expression of ethylene biosynthesis gene PpACO1 in the roots treated with Cd stress. Overall, the application of EBR alleviated Cd-induced oxidative stress in addition to improving root elongation and lateral root growth crosstalk with auxin and ethylene in Kentucky bluegrass subjected to Cd stress. This study further highlights the potential role of brassinosteroids in improving the efficiency of phytoremediation for Cd-contaminated soils.

Effect of arbuscular mycorrhizal fungi (Glomus mosseae) and elevated air temperature on Cd migration in the rhizosphere soil of alfalfa

Cadmium (Cd) migration in the rhizosphere soil is easily affected by plants and microorganisms. Global warming significantly affects plant growth, and arbuscular mycorrhizal fungi (AMF) can chelate heavy metals by mycelium, cell wall components, and mycelial secretion. Here, we investigated the regulation of Glomus mosseae on Cd migration in the rhizosphere soil of alfalfa under elevated temperature (ET, + 3 °C). Elevated temperature significantly decreased G. mosseae colonization rate in the roots by 49.5% under Cd exposure. Under ET + G. mosseae + Cd relative to ET + Cd, the contents of free amino acids, total and easily extractable glomalin-related soil protein (GRSP), and root Cd increased significantly; however, the changes in DTPA-Cd in the rhizosphere soil and Cd in the shoots were insignificant. In addition, G. mosseae colonization enhanced the bioconcentration factor of Cd in the roots and the total removal rate of Cd in the rhizosphere soil by 63.4% and 16.3%, respectively, under ET + Cd. However, the changes in the expression of iron-regulated transport 1 (IRT1) and natural resistance-associated macrophage protein 1 genes were insignificant under ET + G. mosseae + Cd relative to ET + Cd. In summary, temperature and G. mosseae significantly affected Cd fate in the rhizosphere soil, and IRT1 gene and rhizosphere soil pH, N, and C/N ratio were significant factors influencing Cd migration. Additionally, G. mosseae improved the remediation efficiency of Cd-contaminated soils by alfalfa under ET. The results will help us understand the regulation of AMF on the phytoremediation of heavy metal-contaminated soils under global warming scenarios.

Role and Mechanism of Low Molecular-Weight-Organic Acids in Enhanced Phytoremediation of Heavy Metal Contaminated Soil

Phytoremediation is an environmentally friendly technology to remove heavy metals from polluted soil by using the physical and chemical roles of plants. This can effectively reduce the production of secondary pollutants and is economically feasible. Low molecular-weight-organic acids (LMWOAs) are biodegradable and environmentally friendly and have strong application potential in the phytoremediation of heavy metal-contaminated soils. The role and mechanism of LMWOAs in phytoremediation was elaborated on in this study with the aim to:① regulate the development of roots, stems, and leaves; increase plant biomass; and enhance plant enrichment of heavy metals; ② improve photosynthesis, enhance plant resistance, and promote tolerance to heavy metals; ③ change the properties of rhizosphere soil, improve rhizosphere microbial activity, and promote the absorption of heavy metals; and ④ change the form of heavy metals, reduce the toxicity of heavy metals, and improve transport efficiency. Moreover, the advantages, disadvantages, and application of LMWOAs in enhanced phytoremediation of heavy metal-contaminated soil were explored in this study. Finally, the research direction of LMWOAs in the phytoremediation of heavy metal-contaminated soils was proposed, which will have practical scientific significance for the research and application of LMWOAs in future phytoremediation.

Identification and Analysis of bZIP Family Genes in Sedum plumbizincicola and Their Potential Roles in Response to Cadmium Stress.

Sedum plumbizincicola (Crassulaceae), a cadmium (Cd)/zinc (Zn)/lead (Pb) hyperaccumulator native to Southeast China, is potentially useful for the phytoremediation of heavy metal-contaminated soil. Basic leucine zipper (bZIP) transcription factors play vital roles in plant growth, development, and abiotic stress responses. However, there has been minimal research on the effects of Cd stress on the bZIP gene family in S. plumbizincicola. In this study, 92 SpbZIP genes were identified in the S. plumbizincicola genome and then classified into 12 subgroups according to their similarity to bZIP genes in Arabidopsis. Gene structure and conserved motif analyses showed that SpbZIP genes within the same subgroup shared similar intron–exon structures and motif compositions. In total, eight pairs of segmentally duplicated SpbZIP genes were identified, but there were no tandemly duplicated SpbZIP genes. Additionally, the duplicated SpbZIP genes were mainly under purifying selection pressure. Hormone-responsive, abiotic and biotic stress-responsive, and plant development-related cis-acting elements were detected in the SpbZIP promoter sequences. Expression profiles derived from RNA-seq and quantitative real-time PCR analyses indicated that the expression levels of most SpbZIP genes were upregulated under Cd stress conditions. Furthermore, a gene co-expression network analysis revealed that most edge genes regulated by hub genes were related to metal transport, responses to stimuli, and transcriptional regulation. Because its expression was significantly upregulated by Cd stress, the hub gene SpbZIP60 was selected for a functional characterization to elucidate its role in the root response to Cd stress. In a transient gene expression analysis involving Nicotiana benthamiana leaves, SpbZIP60 was localized in the nucleus. The overexpression of SpbZIP60 enhanced the Cd tolerance of transgenic Arabidopsis plants by inhibiting ROS accumulation, protecting the photosynthetic apparatus, and decreasing the Cd content. These findings may provide insights into the potential roles of the bZIP family genes during the S. plumbizincicola response to Cd stress.

Integration of manganese accumulation, subcellular distribution, chemical forms, and physiological responses to understand manganese tolerance in Macleaya cordata.

Macleaya cordata (Willd.) R. Br. are proposed for the application in phytoremediation of heavy metal-contaminated soil. In this paper, the physiological response, subcellular distribution, chemical form, ultrastructure, and manganese (Mn) absorption characteristics of M. cordata under the stress of 0, 3, 6, 9, 12, and 15mmol/L manganese concentration were studied by sand culture experiment. The results showed that M. cordata seedlings show high tolerance to Mn stress with a concentration of less than 6mmol/L, while higher Mn concentration showed a significant toxic effect. A low concentration of Mn (≤ 6mmol/L) can promote the synthesis of chlorophyll and soluble protein; furthermore, superoxide dismutase and peroxidase activities responded positively. The accumulation of Mn in the inactive metabolic part (cell wall and vacuole) of M. cordata leaves might be one of the main Mn detoxification mechanism. According to the ultrastructure of M. cordata, high-concentration Mn2+ (≥ 12mmol/L) stress can cause M. cordata cells to be distorted and deformed, black precipitates appeared in the intercellular space, mitochondria decrease, chloroplasts shrink, hungry particles increased, and starch granules decrease. The uptake ability of different tissues for Mn is leaf > root > stem, and transport coefficient decreases with the increase of Mn concentration. Clearly, M. cordata has a certain tolerance to manganese, which has the ecological application potential in Mn-polluted areas.

Global perspectives and future research directions for the phytoremediation of heavy metal-contaminated soil: A knowledge mapping analysis from 2001 to 2020

Global perspectives and future research directions for the phytoremediation of heavy metal-contaminated soil: A knowledge mapping analysis from 2001 to 2020

Polyaspartic acid alleviates cadmium toxicity in rapeseed leaves by affecting cadmium translocation and cell wall fixation of cadmium

Polyaspartic acid (PASP) is a macromolecule compound with carboxylic acid side chains which is polymerized by L-aspartic acid, has been used as a biodegradable and environmentally-friendly chelating agent to enhance the phytoremediation of heavy metal-contaminated soils. Cadmium (Cd) is a toxic element for plant growth, productivity, and food security. To reveal the responses of PASP to plant physiology and morphology under Cd stress, we comprehensively analyzed soil characteristics, cell ultrastructure, reactive oxygen species (ROS), antioxidant enzymes, Cd uptake, transport, subcellular distribution, cell wall compositions, and their Cd chelating capacity in rapeseed. The results showed PASP increased the content of total N, total P, and available P in soil by 3.4%, 28.6%, and 39.8%, respectively, but did not change soil pH and available Cd. Meanwhile, PASP promoted dry mass accumulation and increased photosynthetic pigment content in rapeseed leaves by maintaining the chloroplast structure. Lower malondialdehyde (MDA) content and hydrogen peroxide (H2O2) accumulation and activated antioxidant enzymes in leaves indicate that PASP contributed to relieving Cd-induced oxidative damage to cells of rapeseed leaves. The results indicated that PASP application increased the Cd distribution ratio in root cell walls from 47.4% to 62.3% and decreased the Cd content in xylem sap by 37.8%, which ultimately reduced Cd reallocation in leaves. Additionally, higher pectin content and Cd in pectin resulted in higher Cd retention in leaf cell walls while reducing its concentration in the organelle fraction. The results indicated that 0.3% PASP effectively alleviated Cd stress in rapeseed leaves by inhibiting Cd transportation from roots, activating antioxidant enzymes to scavenge ROS, and promoting Cd chelation by cell wall pectin in leaves.

Isolation, characterization, and evaluation of a high-siderophore-yielding bacterium from heavy metal-contaminated soil.

Heavy metal-resistant siderophore-producing bacteria (SPB) with plant growth-promoting traits can assist in phytoremediation of heavy metal-contaminated soil. We isolated siderophore-producing bacteria from Pb and Zn mine soil in Shangyu, Zhejiang, China. The isolate with the highest siderophore production, strain SX9, was identified as Burkholderia sp. Burkholderia sp. SX9 produced catecholate-type siderophore, with the highest production at a pH range of 6.0 to 8.0, a temperature range of 20 to 30 °C and NaCl concentration below 2%. Siderophore production was highest without Fe3+ and became gradually lower with increasing Fe3+ concentration. Minimal inhibitory concentrations (MIC) of Pb2+, Zn2+, Cu2+, and Cd2+ were 4000, 22000, 5000, and 2000 μmol L-1, respectively. The strain had a strong metal solubilization ability: the contents of Cu2+, Zn2+, and Cd2+ in the supernatant were 47.4%, 133.0%, and 35.4% higher, respectively, in strain SX9-inoculated cultures than in the not inoculated controls. The siderophore produced by strain SX9 could combine with Fe3+, Zn2+, and Cd2+ with good effectiveness. The plant growth-promoting traits of the strain included indole acetic acid (IAA) production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, and phosphate solubilization capability. Compared to the uninoculated growth medium and SX9 culture supernatant, the germination rate of Lolium perenne seeds was higher when inoculated with strain SX9 culture. In the experiment of seed germination, adding bacterial culture or supernatant could alleviate the toxicity of heavy metals to L. perenne seed germination. Under Cu2+ and Zn2+ stress, strain SX9 promoted the germination rate. Taken together, Burkholderia sp. SX9 had properties beneficial in the microbial enhancement of phytoremediation of soil contaminated with heavy metals.

Bacterial inoculant-assisted phytoremediation of heavy metal-contaminated soil: Inoculant development and the inoculation effects

Bacterial inoculant-assisted phytoremediation of heavy metal-contaminated soil: Inoculant development and the inoculation effects