Zn-polluted Soil Research Articles

Effect of Multi-Walled Carbon Nanotubes, Salicylic Acid, and Drought Stress on Mazut Biodegradation Efficiency in a Pb- and Zn-Polluted Soil Under Cultivation of the Pinto Bean Inoculated with Piriformospora indica

Abstract Aims: Today, remediation of soils contaminated with heavy metals and petroleum compounds is one of the major environmental problems. This research was done to investigate the effect of multiwall carbon nanotubes (MWCNs) and foliar application of salicylic acid (SA) on biodegradation of mazut in the Pb- and Zn-polluted soil under cultivation of the pinto bean inoculated with Piriformospora indica (P.indica). Methods: Treatments included applying MWCNs (0 and 2 % (W/W)) in the soil that was naturally polluted with Pb and Zn, foliar application of salicylic acid at the rate of 0 and 1.5 mmol/lit on the plants inoculated with P.indica under drought stress. In addition, the studied soil was polluted with mazut at the rate of 0% and 6% (w/w). After 3 months, plants were harvested and the plant Pb and Zn, the soil Pb and Zn, and the biodegradation of mazut in the soil were also measured. Results: Addition of MWCNS and foliar application of salicylic acid at the rate of 1.5 mmo/lit significantly decreased the soil Pb by 14.3 and 13.3%, respectively. Plant inoculation with P. indica significantly increased the biodegradation of mazut in the Pb- and Zn-polluted soil by 15.9%. However, drought stress had a negative effect on degradation of mazut in the soil. Conclusion: Regardless of plant expose to drought stress, using MWCNs and foliar application of SA has a positive effect on biodegradation of petroleum hydrocarbon in the soil.

Zinc phytotoxicity and cationic micronutrients contents in quinoa as influenced by high Zn levels and soil amendments

Contamination of soils with heavy metals (HMs) is a serious concern due to the non-biodegradability and accumulation of these metals in living organism. The aim of this study was to evaluate the effectiveness of fish scale powder, chitin, and chitosan in reducing zinc (Zn) accumulation of quinoa grown on Zn-polluted soil. A 3*4 factorial greenhouse trial was conducted with three levels of Zn contamination (0, 100, and 200 mg kg−1) and four types of amendment (control, and 0.15% of each fish scale powder, chitin, and chitosan). The quinoa seeds were sown in soil treated with Zn contamination and amendments. Results showed that application of amendments especially chitosan increased shoot and root dry weight and greenness index of quinoa leaf. While high soil Zn levels decreased cationic micronutrients uptake in quinoa shoot, chitosan addition desirably enhanced cationic micronutrients uptake in quinoa shoot. Overall, amendment addition significantly decreased Zn concentration and uptake in plant; the highest decrease was observed following the application of chitosan. Although the application of high Zn levels significantly increased the values of phytoextraction efficiency, application of chitin and chitosan significantly decreased it. The value of translocation factor was lower than one, demonstrating that a large amount of Zn was stabilized in the root tissues, while a small amount of this metal was transferred to aboveground parts of quinoa. Results of this study revealed that fish scales derivatives were effective in preventing Zn toxicity and at the same time increasing cationic micronutrients contents of quinoa grown on HMs-polluted soil.

Evaluation of effects of animal dung composites and Bacillus sp in amended bioremediation of Zn-polluted soil on maize seedlings growth

Heavy metal pollution of arable soils reduces their productivity, hence the need for ecofriendly techniques to ameliorate this increasing menace. In this study, cow dung, poultry wastes and their composites were applied as organic supplements, together with Bacillus sp as plant growth promoting rhizobacteria to amend bioremediation of zinc-polluted soil sample. Effects of amendments on physicochemical, mineral contents, and dehydrogenase activity of soil, as well as on corn seedlings growth rate, protein and chlorophyll contents and bioaccumulation of Zn were analyzed. Results demonstrated an increase in pH and nutrient contents including N, organic carbon, soil organic matter, K etc., of amended soil samples. Amendment with composite of two organic supplements produced highest increase in dehydrogenase activity, recording 2.35±2.04 µgTPFg-1h-1 at 33.75 mg/kg, and 2.19±0.04 µgTPFg-1h-1 at 52.55 mg/kg level of Zn pollution. Number of leaves recorded in most samples reduced with increasing Zn pollution, with seedlings grown on soil samples amended with cow dung alone outperforming others and recorded 10.3±0.5, 11.3±0.5 and 12.3±0.5 leaves at 32.75 mg/kg, 42.02 mg/kg and 52.44 mg/kg levels of Zn pollution respectively. Heights of seedlings in most of amendments also decreased with increasing Zn pollution. Also, seedlings grown on samples treated with cow dung alone were tallest, and recorded 109.0±3.4 cm, 115.8±4.3 cm and 127.3±2.6 cm at 32.75 mg/kg, 42.02 mg/kg and 52.44 mg/kg levels of Zn pollution respectively. Zn bioaccumulation different parts of corn seedlings was generally in the order; roots>leaves>stems, while it was; control samples>composite of poultry wastes and cow dung samples>only poultry wastes samples>only cow dung samples, for various treatments. This buttresses the usefulness of organic amendments, especially cow dung, in bioremediation of Zn-polluted soil used for agricultural activities.

Zinc toxicity and tolerance-related responses in Inga marginata and Allophylus edulis seedlings

Although zinc (Zn) is a micronutrient, excessive amounts in the soil can have toxic effects on plants. Fertilizers, limestone materials, pesticides, and fungicides added with Zn have contributed to increasing the concentration of this element in agricultural soils. Accordingly, it is necessary to find Zn-tolerant plant species to be properly used in degraded soil restoration programs. Thus, the current study aims to investigate the influence of different Zn concentrations on photosynthetic variables, antioxidant activity, and growth of I. marginata and A. edulisseedlings to determine their potential to be used as phytoremediation species. The experiment was installed in a 2×5 factorial scheme, with the first factor being two species (Allophylus edulis and Inga marginata), and the second factor: five concentrations of Zn (2, 75, 150, 225, and 300 μM), with three replications per treatment. Each sampling unit consisted of a pot with five plants. Photosynthetic, morphological variables of the shoot and root systems, chlorophyll a fluorescence, photosynthetic pigments, antioxidant enzyme activity, lipid peroxidation, hydrogen peroxide concentration, and Zn accumulated in the roots and shoot were evaluated. Zn stress has activated an efficient antioxidant system, which reduced oxidative damage in the leaves of both species; consequently, it did not decrease shoot biomass production in Inga marginata and Allophylus edulis seedlings. High Zn accumulation in plant tissues and lack of negative effects on Inga marginata and Allophylus edulis shoot have suggested that these plant species are tolerant to Zn and may be indicated for Zn-polluted soil phytoremediation purposes.

Sepiolite, Palygorskite, and Triple Super Phosphate on the Uptake of Heavy Metals by Two Iranian Wheat Cultivars Inoculated With Piriformospora indica Fungus

Background and Purpose: Soil remediation in contaminated soils is an important factor of environmental research. This research evaluated the effect of sepiolite, palygorskite, and triple super phosphate (TSP) on decreasing the heavy metals uptake by wheat cultivars inoculated with Piriformospora indica (P. indica). Materials and Methods: Treatments included applying sepiolite, palygorskite (at the rate of 0% and 5% (W/W), and TSP (0% and 0.5% W/W) in the Pb- and Zn-polluted soil under cultivation of 2 wheat cultivars (Mihan and Pishgam cultivars) that inoculated with P. indica fungus. Plants were harvested after 90 days, and Pb and Zn concentrations in soils and plants were measured using atomic absorption spectroscopy. Furthermore, the catalase (CAT) enzyme activity was also measured. Results: With applying 5% (W/W) sepiolite and palygorskite, the plant Pb concentration was significantly reduced by 11.8%, while the plant Zn concentration increased by 13.9%. Plant Zn and Pb concentrations considerably increased and decreased following plant inoculation. However, plant cultivars showed different results. Our results showed that the Pb and Zn concentrations were lower in Mihan than in the Pishgam wheat cultivar. In addition, increasing soil Pb availability caused a significant increase in CAT enzyme activity. Soil contamination with heavy metals had a negative impact on plant root colonization. Conclusion: The interaction of plant cultivars and P. indica significantly affected plant heavy metal uptake by plants. However, environmental studies have found that applying organic amendments like nan-clays or TSP can reduce the absorption of Pb by plants.

Accumulation and distribution of zinc in rice plants (Oryza sativa L.) growing in zinc contaminated paddy soils with biochar

At low concentrations zinc (Zn) is essential for plants and animals, but it becomes toxic when it exceeds a critical level. This study aimed to explore the effects of biochar on the remediation of Zn-polluted soil and the distribution of Zn in rice plants using pot experiments. Various amounts of biochar (0% (control), 2.5%, and 5% w/w) derived from rice straw were mixed with Zn-contaminated soil collected from farmland near a mine. The results showed that biochar enhanced the biomass of rice tissues and significantly reduced the concentration of Zn in brown rice. These results could be attributed to the combination of several effects: (1) Biochar increased the soil pH and organic carbon content, resulting in a reduction in the concentration of soil available Zn and transforming forms of immobilized Zn from acid soluble to reducible. (2) Biochar addition decreased the amorphous iron and complex iron concentrations in the soil solution and reduced the formation of root Fe plaques as well as the storage of Zn in iron plaques, thus diminishing the probability of Zn transfer from root surfaces to tissues. (3) Biochar played a key role in abating the toxic effect of Zn in rice plants as it decreased the transfer of Zn from roots to leaves and promoted Zn storage in the vacuoles of root cells. These results suggest that the application of biochar to Zn-contaminated soil is effective in reducing Zn accumulation in rice grains and can enhance rice production.

Mineral Inactivation of Zinc in Polluted Soil—Sustainability of Zeolite, Bentonite and Blends

The study outlines a novel and traceable procedure for inactivating zinc polluted soil (an Anthrosols) adjacent to a former zinc (Zn) ore mine “Orzel Biały” in Bytom (Poland), where the total content of Zn amounted to 3988.0 mg kg−1. This pollution level initiated an inactivation process involving two natural mineral sorbents, i.e., zeolite (Z) and bentonite (B), as well as their five blends (ZeoBen) expressed as ZB: (1) ZB15/85, (2) ZB30/70, (3) ZB50/50, (4) ZB70/30 and (5) ZB85/15. Next, phosphorus (P) as triple superphosphate (TSP, 46% P2O5) was added to individual ZB at rates: 0.25%, 0.5%, 1.0% and 2.0%. All sorbents were added to the Zn polluted soil at 0%, 0.25%, 0.5%, 1.0% and 2.0% (dry weight basis). Treatments (1.0 kg of Zn-polluted soil with ZB sorbents) were aged for 115 days. Data revealed that ZB85/15 with prevailing zeolite caused a Znact inactivation of 66–71%, while zeolite induced 54% and 47% for bentonite. Reactive zinc (Znreac) decreased much more (20%) when zeolite was incorporated at the rate 2.5 g·kg−1 soil, and bentonite was (10%) at the same rate. The application of the sorbent ZB50/50 enriched with triple superphosphate (TSP) raised the stabilization degree for both Zn fractions. The efficiency was significant at the TSP rate of 2.0% of the sorbent and at least the sorbent +TSP of 10 g·kg−1 soil. The cation exchange capacity (CEC) of about 2 cmol(+)·kg−1 controlled the activity −0.50 mmol·dm−3 of either γZnreac or γZnact, hence a very low zinc ionic activity. The use of mineral blends with higher sharing of zeolite is promising for remediating metal-polluted lands in the case of zinc.

Enhancement of Zn tolerance and accumulation in plants mediated by the expression of Saccharomyces cerevisiae vacuolar transporter ZRC1

Main conclusionTransgenic Arabidopsis thaliana and Populus alba plants overexpressing the zinc transporter ScZRC1 in shoots exhibit Zn tolerance. Increased Zn concentrations were observed in shoots of P. alba, a species suitable for phytoremediation.Genetic engineering of plants for phytoremediation is worth to consider if genes leading to heavy metal accumulation and tolerance are expressed in high biomass producing plants. The Saccharomyces cerevisiae ZRC1 gene encodes a zinc transporter which is primarily involved in the uptake of Zn into the vacuole. The ZRC1 gene was expressed in the model species A. thaliana and P. alba (cv. Villafranca). Both species were transformed with constructs carrying ScZRC1 under the control of either the CaMV35S promoter for constitutive expression or the active promoter region of the tobacco Rubisco small subunit (pRbcS) to limit the expression to the above-ground tissues. In hydroponic cultures, A. thaliana and poplar ScZRC1-expressing plants accumulated more Zn in vegetative tissues and were more tolerant than untransformed plants. No differences were found between plants carrying the CaMV35::ScZRC1 or pRbcS::ScZRC1 constructs. The higher Zn accumulation in transgenic plants was accompanied by an increased superoxide dismutase (SOD) activity, indicating the activation of defense mechanisms to prevent cellular damage. In the presence of cadmium in addition to Zn, plants did not show symptoms of metal toxicity, neither in hydroponic cultures nor in soil. Zn accumulation increased in shoots, while no differences were observed for Cd accumulation, in comparison to control plants. These data suggest that ectopic expression of ScZRC1 can increase the potential of poplar for the remediation of Zn-polluted soils, although further tests are required to assay its application in remediating multimetal polluted soils.

Phytoremediation of zinc polluted soil using sunflower (Helianthus annuus L.)

This study aimed at assessing the ability of sunflower to remediate zinc (Zn) impacted soils and the partitioning factors of Zn in soil-plants interactions. The research method used ex situ experiments using teddy bear sunflower seeds with 8 different treatments for each. This began with the preparation of the sample soil media on garden soil, and the seeding of sunflower seeds. This research was carried out for six months starting in August - December 2020, with Helianthus annuus plants with variations of the Zn. Various concentrations of Zn were applied, ranging from 50 ppm to 350 ppm. Laboratory analysis of Zn was carried out using the Atomic Absorption Spectrophotometry (AAS) method. The research results have revealed that roots have the ability to translocate more Zn than shoots, which suggests a phytoremediation mechanism. Sunflower plants are able to translocate Zn, which proves it reliable for phytoremediation of Zn-polluted soil.

Physiological responses of white mustard grown in Zn-contaminated soils

Introducing zinc (Zn) biofortified vegetables capable to thrive on Zn-polluted soils might simultaneously solve both the problems of dietary Zn deficiency and environmental Zn pollution. White mustard (Sinapis alba L.) is known to thrive on soils with high Zn concentrations, thus we aimed to determine to what extent it has physiological characteristics close to known Zn hyperaccumulators for possible use of this species in phytoremediation efforts and production of Zn-biofortified crops. To achieve this, in a pot experiment plants were grown for 7 weeks in soils with normal (25.5 mg kg−1) and excess (500 and 1000 mg kg−1) Zn concentrations and assessed for metal accumulation, enrichment, translocation and tolerance. Zn accumulated mainly in shoots (861 mg kg−1) with translocation factor of 2.5 in parallel with enhanced root H+-ATPase activity but the plant Zn bioconcentration factors were less than one. Excess soil Zn increased plant biomass and activities of some reactive oxygen species scavenging enzymes without any effects on root lipid peroxidation or leaf chlorophyll contents. Despite lack of criteria for a true Zn hyperaccumulator, white mustard exhibited significant Zn trans-location capacity with tolerance to toxic Zn concentrations in tissues as reflected from its efficient antioxidant metabolism, unaltered photosynthetic pigments under excess Zn and high aboveground biomass similar to some Zn hyperaccmulators. Accordingly, the cultivation of this species has the dual advantages of phytoremediating Zn-contaminated soils and producing Zn-biofortified vegetables.

Effect of HEDTA, CDTA, and EGTA Chelates on Remediation of Pb- and Zn-Polluted Soil Using Sunflower and Canola Plants: A Case Study; Soil Around Bama Pb and Zn Mine

Background: The soil heavy metal pollution caused by human activities is one of the main environmental problems. Therefore, it is necessary to use appropriate methods to remediate such soils. Objectives: The current study aimed at investigating the effect of Hydroxyl Ethylene Diamine Tetra Acetic Acid (HEDTA), Trans-1,2-Cyclohexylene Dinitrilo Tetra Acetic Acid (CDTA), and Ethylene Glycol-bis (β-Aminoethyl Ether)-N,N,N’,N’-Tetra Acetic Acid (EGTA) chelates on Pb and Zn removal efficiency in a Pb and Zn contaminated soil. Methods: This research was performed as a factorial experiment in a randomized complete block design with four levels of chelate application rate (0, 1.5, 3, and 4.5 mM/kg soil), two levels of chelates application times (one or two weeks before harvesting), and plant types (sunflower or canola). At the end of the experiment, Pb and Zn concentrations in the soil and plant samples were measured and the least significant difference (LSD) test was employed to determine the differences between the means. Results: The effectiveness of studied chelates on the availability of Zn and Pb in soil was in the descending order as HEDTA > CDTA > EGTA. Application of 4.5 mM/kg soil of CDTA chelate under sunflower and canola cultivation caused a significant increase in the availability of Zn and Pb in soil compared to 1.5 mM/kg by 12.2% and 13.3%, respectively. Plant type also had a significant effect on increasing the availability of Pb and Zn in soil. Conclusions: Plant type, application rate, and chelates type are important factors on remediation of heavy metals in contaminated soil. However, the role of physicochemical properties of soil on its heavy metal availability cannot be ignored.

In situ immobilization of zinc polluted soil using thermal-activated serpentine

ABSTRACTIn situ immobilisation zinc (Zn) in simulated polluted soil was conducted by using the thermal-activated serpentine prepared via heating natural serpentine at different temperatures as amendments. The effects of the amendments on the form of Zn in soil and the potential immobilisation mechanisms were investigated. After Zn polluted soil incubated with serpentine at rates of 3% by weight for 60 d, the pH value of the soil could be obviously increased, and then resulting in reducing the content of TCLP-Zn (toxicity characteristic leaching procedure extractable Zn) in soil. Furthermore, the addition of serpentine, especially the serpentine activated at 700 °C, could promote significantly the transformation from bioavailable Zn speciation to a much less bioavailable speciation, and the ratio of exchangeable and carbonate form of Zn decreased by 34.5%, and the proportion of residual form of Zn increased by 28.5% compared with CK (no-amendment control) treatment. The formation of Zn5(NO3)2(OH)8·2H2O and Zn(NO3)(OH)·H2O as well as surface adsorption were the main immobilisation mechanisms. These results indicated that thermal-activated serpentine had the great potential for immobilisation of Zn in soil, and it would lay a foundation for the construction of high performance amendments of heavy metal.

Effect of spent mushroom substrate on strengthening the phytoremediation potential of Ricinus communis to Cd- and Zn-polluted soil

Phytoremediation is a kind of efficient strategy for remediating soils polluted with heavy metals. The aim of this study was to investigate the influence of spent mushroom substrate (SMS) on the phytoremediation potential of Ricinus communis in Cd- and Zn-polluted soil. We treated the soil with SMS before growing plants and analyzed the contents, distribution of heavy metals, and response of plants after growth. SMS increased the contents of Cd (5%–13%) and Zn (16%–20%) in the cell wall. This finding suggested that high amounts of Cd and Zn were absorbed and bonded to the cell wall through metabolism adaption and formed stable compounds, which reduced the damage of the heavy metal to cells. SMS also decreased the levels of superoxide dismutase, peroxidase, and catalase by 9.5%–27.7%, 8.8%–30.0% and 8.5%–28.1%, respectively. Treatment of SMS alleviated the toxicity of heavy metal in plants and increased the extracted amounts of Zn and Cd by 101%–227% and 51%–189%, respectively. Hence, SMS treatment could reduce the toxicity of heavy metals to plants and strengthen the phytoremediation potential.

Bioethanol production from recovered napier grass with heavy metals

Using plants to absorb and accumulate heavy metals from polluted soil, followed by the recycling of explants containing heavy metals, can help achieve the goal of reverting contaminated soil to low heavy-metal content soil. However, the re-use of recovered explants can also be problematic. Meanwhile, bioethanol has become a popular energy source. In this study, napier grass was used for the remediation of soil contaminated with heavy metals (artificially contaminated soil). The influence of bioethanol production from napier grass after phytoremediation was also investigated. The concentration of Zn, Cd, and Cr in the contaminated soil was 1000, 100, and 250 mg/kg, respectively. After napier grass phytoremediation, the concentration (dry biomass) of Zn, Cd, and Cr in the explants was 2701.97 ± 173.49, 6.1 ± 2.3, and 74.24 ± 1.42 mg/kg, respectively. Biomass production in the unpolluted soil was 861.13 ± 4.23 g. The biomass production ratio in high Zn-polluted soil was only 3.89%, while it was 4.68% for Cd and 21.4% for Cr. The biomass obtained after napier grass phytoremediation was pretreated using the steam explosion conditions of 180 °C, for 10 min, with 1.5% H2SO2, followed by enzymatic hydrolysis. The efficiency of enzymatic hydrolysis for Zn-polluted biomass was 90% of the unpolluted biomass, while it was 77% for Cd, and approximately the same for Cr. The fermentation efficiency of the heavy-metal-containing biomass was higher than the control biomass. The fermentation ethanol concentration obtained was 8.69–12.68, 13.03–15.50, and 18.48–19.31 g/L in Zn, Cd, and Cr environments, respectively. Results show that the heavy metals had a positive effect on bacteria fermentation. However, the fermentation efficiency was lower for biomass with severe heavy metal pollution. Thus, the utilization of napier grass phytoremediation for bioethanol production has a positive effect on the sustainability of environmental resources.

Advances in the use of Halimione portulacoides stem cuttings for phytoremediation of Zn-polluted soils

The salt-marsh shrub Halimione portulacoides can grow in soils containing extremely high concentrations of Zn and stem cuttings have recently been shown to aid the recovery of polluted soils although further work on this methodology have is required. A greenhouse experiment was carried out to analyze the effects of a range of Zn concentrations (0–130 mmol l−1) on the establishment, growth and photosynthetic performance of stem cuttings of different sizes of Halimione portulacoides, with the aim of determine the phytotoxicity thresholds and the optimal initial size of the cuttings to be used in phytoremediation strategies. Stem cuttings were able to survive and grow at external Zn concentrations of 130 mmol l−1. Plants from smaller cuttings showed greater growth inhibition, which could have been related to the inability to establish a root system sufficiently developed so as to avoid the translocation of Zn to aerial parts. The present study demonstrates that stem cuttings of H. portulacoides can establish and develop a root system under concentrations as high as 130 mmol l−1 Zn (approximately 9000 mg kg−1). In highly polluted soils, with concentrations from 50 mmol l−1, it would be advisable to use stem cuttings with a minimum size of approximately 10 cm in length and a minimum biomass of 100 mg dry weight. This study indicate that the use of H. portulacoides stem cuttings could play an important role in the restoration of coastal ecosystems contaminated with heavy metals.

English

Fields experiment was done to investigate the effect of a typical water saving irrigation technique, namely non-flooding controlled irrigation (NFI), on the extractability, solubility, and bioavailability of zinc (Zn) in a non-polluted paddy soil. The Zn contents in the soil solutions, soil extractions by modified BCR (European Community Bureau of Reference) sequential extraction procedure, and the plant digestions were measured. Compared with the Zn in flooding irrigation (FI) soil, Zn contents in extractable (EXT) form and Zn contents in soil solutions was increased in 0–20 cm NFI soil, accompanied with a little reduction of soil Zn in oxidizable (OXD) form. That confirmed the Zn in OXD form was released into soil solution under the wetting-drying cycle condition in NFI fields, and hence resulted in high extractability and solubility of Zn in top surface soil. As a result, Zn contents in the rice plant parts in NFI fields were higher than in FI fields. It can be concluded that NFI irrigation is help to enhance soil Zn bioavailability and food Zn nutrients status in the soil without Zn-pollution and Zn deficiency, but might led to soil Zn depletion in Zn deficient soil or rice foodstuffs pollution in Zn-polluted soil. © 2015 Friends Science Publishers

Residual impact of aged nZVI on heavy metal-polluted soils

In the present study, the residual toxicity and impact of aged nZVI after a leaching experiment on heavy metal (Pb, Zn) polluted soils was evaluated. No negative effects on physico-chemical soil properties were observed after aged nZVI exposure. The application of nZVI to soil produced a significant increase in Fe availability. The impact on soil biodiversity was assessed by fluorescence in situ hybridization (FISH). A significant effect of nZVI application on microbial structure has been recorded in the Pb-polluted soil nZVI-treated. Soil bacteria molecular response, evaluated by RT-qPCR using exposure biomarkers (pykA, katB) showed a decrease in the cellular activity (pykA) due to enhanced intracellular oxidative stress (katB). Moreover, ecotoxicological standardised test on Caenorhabditis elegans (C. elegans) showed a decrease in the growth endpoint in the Pb-polluted soil, and particularly in the nZVI-treated. A different pattern has been observed in Zn-polluted soils: no changes in soil biodiversity, an increase in biological activity and a significant decrease of Zn toxicity on C. elegans growth were observed after aged nZVI exposure. The results reported indicated that the pollutant and its nZVI interaction should be considered to design soil nanoremediation strategies to immobilise heavy metals.

Epigenetic control of heavy metal stress response in mycorrhizal versus non-mycorrhizal poplar plants

It was previously shown that arbuscular mycorrhizal fungi (AMF) exert a significant improvement of growth in a tolerant white poplar (Populus alba L.) clone (AL35) grown on Cu- and Zn-polluted soil via foliar alterations in the levels of defence/stress-related transcripts and molecules. However, nothing is known about the epigenetic changes which occur during tolerance acquisition in response to heavy metals (HMs) in the same mycorrhizal vs. non-mycorrhizal poplar plants. In order to analyse the epigenome in leaves of AL35 plants inoculated or not with AMF and grown in a greenhouse on multimetal polluted or unpolluted soil, the Methylation Sensitive Amplification Polymorphism (MSAP) approach was adopted to detect cytosine DNA methylation. Modest changes in cytosine methylation patterns were detected at first sampling (4 months from planting), whereas extensive alterations (hypomethylation) occurred at second sampling (after 6 months) in mycorrhizal plants grown in the presence of HMs. The sequencing of MSAP fragments led to the identification of genes belonging to several Gene Ontology categories. Seven MSAP fragments, selected on the basis of DNA methylation status in treated vs control AL35 leaves at the end of the experiment, were analysed for their transcript levels by means of qRT-PCR. Gene expression varied in treated samples relative to controls in response to HMs and/or AMF inoculation; in particular, transcripts of genes involved in RNA processing, cell wall and amino acid metabolism were upregulated in the presence of AMF with or without HMs.

Zinc export results in adaptive zinc tolerance in the ectomycorrhizal basidiomycete Suillus bovinus

On Zn-polluted soils, populations of the ectomycorrhizal basidiomycete Suillus bovinus exhibit an elevated Zn tolerance when compared to populations on non-polluted sites. To elucidate the mechanism of Zn tolerance, the time-course of Zn uptake was studied in isolates with contrasting Zn tolerance. Unidirectional fluxes and subcellular compartmentation of Zn were investigated through radiotracer flux analyses. Fluorescence imaging was used to support the subcellular Zn compartmentation. After 2 h of exposure to 200 μM Zn, significantly more Zn was accumulated in Zn-sensitive isolates compared to tolerant isolates, despite similar short-term uptake kinetics and similar extracellular Zn sequestration in cell walls. In Zn-sensitive isolates twice as much Zn accumulated in the cytoplasm and 12 times more Zn in the vacuole. (65)Zn efflux analyses revealed a considerably faster Zn export in the Zn-tolerant isolate. The adaptive Zn tolerance in S. bovinus is therefore achieved by a preferential removal of Zn out of the cytoplasm, back into the apoplast, instead of the usual transfer of Zn into the vacuole. Zn exclusion in the fungal symbiont eventually contributes to a lower Zn influx in host plants.

Effect of Zn Stress on <i>Pteris vittata</i>

In order to investigate the ability of Pteris vittata restoring Zn polluted soil, water cultured experiment is utilized to study the enriching ability of Pteris vittata to Zn, and the detoxification mechanism of Pteris vittata to Zn. The experimental results show that Pteris vittata has certain enriching ability to Zn,and the translation coefficient of Zn in Pteris vittata reaches 1.0. With the increasing of Zn application amount, chlorophyll and soluble sugar contents of Pteris vittata show ascending first and then descending,O2-• and MDA contents continuously ascend,starch content continuously descends.These results show that soluble sugar, starch,O2-• and MDA have detoxification effect,and can enhance the resistance of plant to heavy metal.