Arsenic Accumulation In Plants Research Articles

Effects of arbuscular mycorrhizal fungi on the reduction of arsenic accumulation in plants: a meta-analysis.

Arsenic (As) accumulation in plants is a global concern. Although the application of arbuscular mycorrhizal fungi (AMF) has been suggested as a potential solution to decrease As concentration in plants, there is currently a gap in a comprehensive, quantitative assessment of the abiotic and biotic factors influencing As accumulation. A meta-analysis was performed to quantitatively investigate the findings of 76 publications on the impacts of AMF, plant properties, and soil on As accumulation in plants. Results showed a significant dose-dependent As reduction with higher mycorrhizal infection rates, leading to a 19.3% decrease in As concentration. AMF reduced As(V) by 19.4% but increased dimethylarsenic acid (DMA) by 50.8%. AMF significantly decreased grain As concentration by 34.1%. AMF also improved plant P concentration and dry biomass by 33.0% and 62.0%, respectively. The most significant reducing effects of As on AMF properties were seen in single inoculation and experiments with intermediate durations. Additionally, the benefits of AMF were significantly enhanced when soil texture, soil organic carbon (SOC), pH level, Olsen-P, and DTPA-As were sandy soil, 0.8%-1.5%, ≥7.5, ≥9.1 mg/kg, and 30-60 mg/kg, respectively. AMF increased easily extractable glomalin-related soil protein (EE-GRSP) and total glomalin-related soil protein (T-GRSP) by 23.0% and 28.0%, respectively. Overall, the investigated factors had significant implications in developing AMF-based methods for alleviating the negative effects of As stress on plants.

Current perspectives of ACR3 (arsenite efflux system) toward the reduction of arsenic accumulation in plants

Current perspectives of ACR3 (arsenite efflux system) toward the reduction of arsenic accumulation in plants

Effect of Soil Characteristics on Arsenic Accumulation in Phytolith of Gramineae (Phragmites japonica) and Fern (Thelypteris palustris) Near the Gilgok Gold Mine

In South Korea, most metal mines were abandoned and caused contamination for more than 30 years. Even the soil is highly contaminated with trace elements, plants still grow in the area and can affect the contamination. Phytolith is amorphous silica in the plant body. Phytolith is resistant to decomposition, and the stabilization of carbon, nutrients, and toxic substances accumulated in the phytolith is being studied. In this study, the Gilgok gold mine, which is contaminated with arsenic was selected as the research site. We selected Phragmites japonica and Thelypteris palustris as targets for the analysis of arsenic accumulation in plants and phytolith. Plants accumulate more phytolith at the riverside. The higher water content of soil increased the Arsenic (As) concentration in the frond of the T. palustris. Soil available silicon (Si) did not affect phytolith accumulation but increased As accumulation in the plant and phytolith. The research result showed that P. japonica and T. palustris have the ability to accumulate As in phytolith and the accumulation can be changed with soil characteristics and plant species. This As accumulation in phytolith can affect plant tolerance in contaminated areas and change the As availability in the soil. The result of the research can be used as a database to build a sustainable environment.

Decreases in arsenic accumulation by the plasma membrane intrinsic protein PIP2;2 in Arabidopsis and yeast.

Arsenic (As) is a toxic pollutant that mainly enters the human body via plants. Therefore, understanding the strategy for reducing arsenic accumulation in plants is important to human health and the environment. Aquaporins are ubiquitous water channel proteins that bidirectionally transport water across cell membranes and play a role in the transportation of other molecules, such as glycerol, ammonia, boric acid, and arsenic acid. Previously, we observed that Arabidopsis PIP2;2, encoding a plasma membrane intrinsic protein, is highly expressed in NtCyc07-expressing Arabidopsis, which shows a higher tolerance to arsenite (As(III)). In this study, we report that the overexpression of AtPIP2;2 enhanced As(III) tolerance and reduced As(III) levels in yeast. Likewise, AtPIP2;2-overexpressing Arabidopsis exhibited improved As(III) tolerance and lower accumulation of As(III). In contrast, atpip2;2 knockout Arabidopsis showed reduced As(III) tolerance but no significant change in As(III) levels. Interestingly, the AtPIP2;2 transcript and protein levels were increased in roots and shoots of Arabidopsis in response to As(III). Furthermore, As(III) efflux was enhanced and As(III) influx/accumulation was reduced in AtPIP2;2-expressing plants. The expression of AtPIP2;2 rescued the As(III)-sensitive phenotype of acr3 mutant yeast by reducing As levels and slightly reduced the As(III)-tolerant phenotype of fps1 mutant yeast by enhancing As content, suggesting that AtPIP2; 2 functions as a bidirectional channel of As(III), while the As(III) exporter activity is higher than the As(III) importer activity. All these results indicate that AtPIP2;2 expression promotes As(III) tolerance by decreasing As(III) accumulation through enhancing As(III) efflux in Arabidopsis. This finding can be applied to the generation of low arsenic crops for human health.

Study on Arsenic Poisoning by Worldwide Drinking Water, its Effects and Prevention

The present studies were conducted to evaluate the arsenic poisoning worldwide in drinking water. Arsenicnot only contaminates the surface and groundwater but also enters into food chains like vegetables and food staff.Human beings are directly exposed to arsenic poisoning due to consumption of water resources containing arsenic. Seafoods and fish are two main sources of arsenic in human diet. Consumption of arsenic poisoned water can cause severehealth problems like cancer, hyperkeratosis, gangrene and peripheral vascular diseases. The arsenic is excreted from thebody trough skin, hair, urine, breath etc. Arsenic poisoning can be diagnosed by the measurement of total amount ofarsenic in urine. Symptoms of arsenic poisoning include red or swollen skin, changes in the skin color, abdominal pain,vomiting and nausea, diarrhea, cramping of muscles, finger and toe tingling etc. Arsenic poisoning may be relievedthrough steroid ingestion at its early stage or use of selenium. It is very difficult to remove all the arsenic from waterbodies so the main remedy is to stop drinking water having arsenic content. Arsenic poisoning also affects the plant ‘syield, its reproductive capacity, fertility and fruit production. Arsenic accumulation in plants will damage the cellularmembranes and may lead to the leaking of electrolyte.

Study on Arsenic Poisoning by Worldwide Drinking Water, its Effects and Prevention

The present studies were conducted to evaluate the arsenic poisoning worldwide in drinking water. Arsenicnot only contaminates the surface and groundwater but also enters into food chains like vegetables and food staff.Human beings are directly exposed to arsenic poisoning due to consumption of water resources containing arsenic. Seafoods and fish are two main sources of arsenic in human diet. Consumption of arsenic poisoned water can cause severehealth problems like cancer, hyperkeratosis, gangrene and peripheral vascular diseases. The arsenic is excreted from thebody trough skin, hair, urine, breath etc. Arsenic poisoning can be diagnosed by the measurement of total amount ofarsenic in urine. Symptoms of arsenic poisoning include red or swollen skin, changes in the skin color, abdominal pain,vomiting and nausea, diarrhea, cramping of muscles, finger and toe tingling etc. Arsenic poisoning may be relievedthrough steroid ingestion at its early stage or use of selenium. It is very difficult to remove all the arsenic from waterbodies so the main remedy is to stop drinking water having arsenic content. Arsenic poisoning also affects the plant ‘syield, its reproductive capacity, fertility and fruit production. Arsenic accumulation in plants will damage the cellularmembranes and may lead to the leaking of electrolyte.

Removal of Fluoride and Arsenic by a Hybrid Constructed Wetland System.

A pilot-scale hybrid wetland system was constructed for the removal of fluoride and arsenic from synthetic wastewater. After five months of operation, the fluoride and arsenic removal rate were at the value of 65 % and 90 %, respectively. Through calculation, the accumulation of fluoride in plants only accounted for 1.63 % of the accumulation in substrates, and the accumulation of arsenic in plants accounted for 3.3 % of that in substrates. Both the accumulation of fluoride and arsenic in plants were much higher in roots than that in leaves. And for substrates, the accumulation in the first layer was higher than the second layer. The changes of microbial community in the substrate of the wetland during the operation were also analyzed to investigate the effects of operating condition on the microbial community and to study the role of microorganism on the removal of fluoride and arsenic. The results showed that the relative abundance of Firmicutes reduced, while the relative abundance of Proteobacteria increased, indicating that the fluoride and arsenic in solution had a great influence on the microbial community. Findings of this study suggest that the hybrid constructed wetland system may be a promising process for the removal of fluoride and arsenic from synthetic wastewater.

High External K+ Concentrations Impair Pi Nutrition, Induce the Phosphate Starvation Response, and Reduce Arsenic Toxicity in Arabidopsis Plants.

Potassium (K+) and phosphorous (Pi) are two of the most important nutrients required by plants and there is an interest in studying how they are acquired. Most studies have focused on the characterization of the mechanisms involved in K+ and Pi uptake and their distribution within the plants, as well as the regulatory mechanisms involved. Evidence is emerging which points to interactions in the nutrition of different nutrients and to the existence of crosstalk in the signaling cascades regulating their acquisition. However, the interaction between K+ and Pi has been scarcely studied. Here we show that high concentrations of K+ in the external solution inhibit Pi uptake and impair Pi nutrition in Arabidopsis plants, resulting in the induction of phosphate starvation response (PSR) and the upregulation of genes encoding root phosphate uptake systems. The high K+-induced PSR depends on the PHR1 and PHL1 transcription factors that are key pieces of Pi signaling in Arabidopsis. Importantly, high K+ reduces arsenic accumulation in plants and its toxic effects. The results presented may help to design strategies to reduce Pi deficiency as well as the accumulation of arsenic in crops.

Vacuolar Phosphate Transporter 1 (VPT1) Affects Arsenate Tolerance by Regulating Phosphate Homeostasis in Arabidopsis.

Arsenate [As(V)] is toxic to nearly all organisms. Soil-borne As(V) enters plant cells mainly through the plasma membrane-localized phosphate (Pi) transporter PHT1 family proteins due to its chemical similarity to Pi. We report here that VPT1, a major vacuolar phosphate transporter which contributes to vacuolar Pi sequestration, is associated with As(V) tolerance in Arabidopsis. vpt1 mutants displayed enhanced tolerance to As(V) toxicity, whereas plants overexpressing VPT1 were more sensitive to As(V) as compared with the wild-type plants. Measurements of arsenic content indicated that vpt1 mutants accumulated less arsenic and, in contrast, up-regulating VPT1 expression contributed to higher levels of arsenic accumulation in plants. To examine further how VPT1 may modulate arsenic contents in plants, we surveyed the expression patterns of all the PHT1 family members that play roles in As(V) uptake, and found that many of the PHT1 genes were down-regulated in the vpt1 mutant as compared with the wild type under Pi-sufficient conditions, but not when Pi levels were low in the medium. Interestingly, As(V) sensitivity assays indicated that As(V) resistance in vpt1 mutants was prominent only under Pi-sufficient but not under Pi-deficient conditions. These results suggest that under Pi-sufficient conditions, loss of VPT1 leads to elevated levels of Pi in the cytosol, which in turn suppressed the expression of PHT1-type transporters and reduced accumulation of arsenic.

Accumulation of arsenic in plants from arsenic contaminated irrigation water

Accumulation of arsenic in plants from arsenic contaminated irrigation water

Arsenic toxicity in the water weed Wolffia arrhiza measured using Pulse Amplitude Modulation Fluorometry (PAM) measurements of photosynthesis

Accumulation of arsenic in plants is a serious South-east Asian environmental problem. Photosynthesis in the small aquatic angiosperm Wolffia arrhiza is very sensitive to arsenic toxicity, particularly in water below pH 7 where arsenite (As (OH)3) (AsIII) is the dominant form; at pH >7 AsO42− (As(V) predominates). A blue-diode PAM (Pulse Amplitude Fluorometer) machine was used to monitor photosynthesis in Wolffia. Maximum gross photosynthesis (Pgmax) and not maximum yield (Ymax) is the most reliable indicator of arsenic toxicity. The toxicity of arsenite As(III) and arsenate (H2AsO42−) As(V) vary with pH. As(V) was less toxic than As(III) at both pH 5 and pH 8 but both forms of arsenic were toxic (>90% inhibition) at below 0.1molm−3 when incubated in arsenic for 24h. Arsenite toxicity was apparent after 1h based on Pgmax and gradually increased over 7h but there was no apparent effect on Ymax or photosynthetic efficiency (α0).

Speciation of arsenic and its accumulation by plants from rhizosphere soils under the influence of Azotobacter and Bacillus bacteria

Our study was aimed at disclosing the effect of rhizosphere bacteria Azotobacter and Bacillus, involved in the composition of biological preparations used in plant cultivation, on arsenic accumulation in plants proceeding with its different phase states in the radical rhizosphere part of soil. The plants like wheat, oats, peas and radish have been grown on the controlled soil with some experimental biopreparations applied. In our experiment we worked on the soils differently contaminated with arsenic. The investigation of arsenic phase state was based on the sequential release of extracts from rhizosphere soils occurring as easily exchangeable, carbonate, organic and Fe hydroxide-associated fractions with As identified. We additionally examined the distribution of As in the extract of ethylenediaminetetraacetic acid (EDTA) and in humic substance: fulvic acids and humic acids. It has been inferred, that As migration in the rhizosphere soil is markedly affected by its forms associated with Fe hydroxides and organic compounds: fulvic acids and extracted EDTA by chelate compounds. The experimental results point out that arsenic associated with Fe hydroxides is basically accumulated in the rhizosphere part of soils in their inoculation by rhizo bacteria. In maximally contaminated soils As can possibly be adsorbed on the cells of Azotobacter and Bacillus soil bacteria capable to create a barrier for its supply into plants. Inoculation of soils by rhizosphere bacteria affected the inter-phase transitions of arsenic in soil of rhizosphere significantly influenced the processes of immobilization and mobilization of arsenic in the system “soil–plant” and its biological availability for plants.

Genome-wide association mapping identifies a new arsenate reductase enzyme critical for limiting arsenic accumulation in plants.

Author SummaryArsenic is a human carcinogen that accumulates from soil into many different food crops, where it presents a significantly increased cancer risk when foods derived from these crops are consumed. Plants naturally control the amount of arsenic they accumulate by first chemically converting arsenate into arsenite, which is then extruded from the roots back into the soil. Because arsenate is a chemical analogue of phosphate, conversion of arsenate in the root to arsenite may also prevent arsenic being efficiently transported to the shoots via the phosphate transport system. The chemical reduction of arsenate to generate arsenite is therefore clearly a key component of a plant's detoxification strategy. Here, we use genetic methods to identify the enzyme responsible for this crucial reaction—HAC1. We show that HAC1 is responsible for arsenate reductase activity in both the outer layer of the root (epidermis) and the inner layer adjacent to the xylem (pericycle). In its absence, the roots return less arsenic to the soil and the shoots accumulate up to 300 times more arsenic. This knowledge creates new opportunities to limit arsenic accumulation in food crops, thereby helping to reduce the cancer risk from this food-chain contaminant.

How plants control arsenic accumulation.

How plants control arsenic accumulation.

In silico and in vivo studies of an Arabidopsis thaliana gene, ACR2, putatively involved in arsenic accumulation in plants

Previously, our in silico analyses identified four candidate genes that might be involved in uptake and/or accumulation of arsenics in plants: arsenate reductase 2 (ACR2), phytochelatin synthase 1 (PCS1) and two multi-drug resistant proteins (MRP1 and MRP2) [Lund et al. (2010) J Biol Syst 18:223-224]. We also postulated that one of these four genes, ACR2, seems to play a central role in this process. To investigate further, we have constructed a 3D structure of the Arabidopsis thaliana ACR2 protein using the iterative implementation of the threading assembly refinement (I-TASSER) server. These analyses revealed that, for catalytic metabolism of arsenate, the arsenate binding-loop (AB-loop) and residues Phe-53, Phe-54, Cys-134, Cys-136, Cys-141, Cys-145, and Lys-135 are essential for reducing arsenate to arsenic intermediates (arsenylated enzyme-substrate intermediates) and arsenite in plants. Thus, functional predictions suggest that the ACR2 protein is involved in the conversion of arsenate to arsenite in plant cells. To validate the in silico results, we exposed a transfer-DNA (T-DNA)-tagged mutant of A. thaliana (mutation in the ACR2 gene) to various amounts of arsenic. Reverse transcriptase PCR revealed that the mutant exhibits significantly reduced expression of the ACR2 gene. Spectrophotometric analyses revealed that the amount of accumulated arsenic compounds in this mutant was approximately six times higher than that observed in control plants. The results obtained from in silico analyses are in complete agreement with those obtained in laboratory experiments.

Influence of glutathione chemical effectors in the response of maize to arsenic exposure

To support the key role of glutathione (GSH) in the mechanisms of tolerance and accumulation of arsenic in plants, this work examines the impact of several effectors of GSH synthesis or action in the response of maize (Zea mays L.) to arsenic. Maize was exposed in hydroponics to iso-toxic rates of 150μM arsenate or 75μM arsenite for 9days and GSH effectors, flurazole (an herbicide safener), l-buthionine-sulfoximine (BSO, a known inhibitor of GSH biosynthesis), and dimercaptosuccinate (DMS) and dimercaptopropanesulfonate (DMPS) (two thiols able to displace GSH from arsenite-GSH complexes) were assayed. The main responses of plants to arsenic exposure consisted of a biomass reduction (fresh weight basis) of about 50%, an increase of non-protein thiol (NPTs) levels (especially in the GSH precursor γ-glutamylcysteine and the phytochelatins PC2 and PC3) in roots, with little effect in shoots, and an accumulation of between 600 and 1000ppm of As (dry weight basis) in roots with very little translocation to shoots. Growth inhibition caused by arsenic was partially or completely reversed in plants co-treated with flurazole and arsenate or arsenite, respectively, highly exacerbated in plants co-treated with BSO, and not modified in plants co-treated with DMS or DMPS. These responses correlated well with an increase of both NPTs levels in roots and glutathione transferase activity in roots and shoots due to flurazole treatment, the decrease of NPTs levels in roots caused by BSO and the lack of effect on NPT levels caused by both DMS and DMPS. Regarding to arsenic accumulation in roots, it was not modified by flurazole, highly reduced by BSO, and increased between 2.5- and 4.0-fold by DMS and DMPS. Therefore, tolerance and accumulation of arsenic by maize could be manipulated pharmacologically by chemical effectors of GSH.

Interactions of arsenic and phenanthrene on their uptake and antioxidative response in Pteris vittata L.

The interactions of arsenic and phenanthrene on plant uptake and antioxidative response of Pteris vitatta L. were studied hydroponically. The combination of arsenic and phenanthrene decreased arsenic contents in fronds by 30–51%, whereas increased arsenic concentrations 1.2–1.6 times in roots, demonstrating the suppression of arsenic translocation compared to the corresponding treatment without phenanthrene. Under the co-exposure, As(III) concentrations in fronds deceased by 12–73%, and at higher arsenic exposure level (≥10 mg/L), As(V) in fronds and As(III) in roots increased compared to the single arsenic treatment. Arsenic exposure elevated phenanthrene concentrations in root by 39–164%. The co-existence of arsenic and phenanthrene had little impact on plant arsenic accumulation, although synergistic effect on antioxidants was observed, suggesting the special physiological process of P. vitatta in the co-exposure and application potential of P. vitatta in phytoremediation of arsenic and PAHs co-contamination.

Effects of arbuscular mycorrhizal inoculation on plants growing on arsenic contaminated soil

Arbuscular mycorrhizal fungi (AMF) may play an important role in phytoremediation of As-contaminated soil. In this study the effects of AMF ( Glomus mosseae, Glomus intraradices and Glomus etunicatum) on biomass production and arsenic accumulation in Pityrogramma calomelanos, Tagetes erecta and Melastoma malabathricum were investigated. Soil (243 ± 13 μg As g −1) collected from Ron Phibun District, an As-contaminated area in Thailand, was used in a greenhouse experiment. The results showed different effects of AMF on phytoremediation of As-contaminated soil by different plant species. For P. calomelanos and T. erecta, AMF reduced only arsenic accumulation in plants but had no significant effect on plant growth. In contrast, AMF improved growth and arsenic accumulation in M. malabathricum. These findings show the importance of understanding different interactions between AMF and their host plants for enhancing phytoremediation of As-contaminated soils.

Selecting Appropriate Forms of Nitrogen Fertilizer to Enhance Soil Arsenic Removal by Pteris Vittata: A New Approach in Phytoremediation

Certain plant species have been shown to vigorously accumulate some metals from soil, and thus represent promising and effective remediation alternatives. In order to select the optimum forms of nitrogen (N) fertilizers for the arsenic (As) hyperaccumulator, Pteris vittata L., to maximize As extraction, five forms of N were added individually to different treatments to study the effect of N forms on As uptake of the plants under soil culture in a greenhouse. Although shoot As concentration tended to decrease and As translocation from root to shoot was inhibited, overall As accumulation was greater due to higher biomass when N fertilizer was added. Arsenic accumulation in plants with N fertilization was 100∼300% more than in the plants without N fertilization. There were obvious differences in plant biomass and As accumulation among the N forms, i.e., NH4HCO3, (NH4)2SO4, Ca(NO3)2, KNO3, urea. The total As accumulation in the plants grown in As-supplied soil, under different forms of N fertilizer, decreased as NH4HCO3>(NH4)2SO4 > urea > Ca(NO3)2 >KNO3>CK. The plants treated with N and As accumulated up to 5.3∼7.97 mg As/pot and removed 3.7∼5.5% As from the soils, compared to approximately 2.3% of As removal in the control. NH4 +-N was apparently more effective than other N fertilizers in stimulating As removal when soil was supplied with As at initiation. No significant differences in available As were found among different forms of N fertilizer after phytoremediation. It is concluded that NH4 +-N was the preferable fertilizer for P. vittata to maximize As removal.

Effects of compost and phosphate on plant arsenic accumulation from soils near pressure-treated wood

Leaching of arsenic (As) from chromated copper arsenate (CCA)-treated wood may elevate soil arsenic levels. Thus, an environmental concern arises regarding accumulation of As in vegetables grown in these soils. In this study, a greenhouse experiment was conducted to evaluate As accumulation by vegetables from the soils adjacent to the CCA-treated utility poles and fences and examine the effects of soil amendments on plant As accumulation. Carrot ( Daucus carota L.) and lettuce ( Lactuca sativa L.) were grown for ten weeks in the soil with or without compost and phosphate amendments. As expected, elevated As concentrations were observed in the pole soil (43 mg kg −1) and in the fence soil (27 mg kg −1), resulting in enhanced As accumulation of 44 mg kg −1 in carrot and 32 mg kg −1 in lettuce. Addition of phosphate to soils increased As accumulation by 4.56–9.3 times for carrot and 2.45–10.1 for lettuce due to increased soil water-soluble As via replacement of arsenate by phosphate in soil. However, biosolid compost application significantly reduced plant As uptake by 79–86%, relative to the untreated soils. This suppression is possibly because of As adsorbed by biosolid organic mater, which reduced As phytoavailability. Fractionation analysis showed that biosolid decreased As in soil water-soluble, exchangeable, and carbonate fraction by 45%, whereas phosphate increased it up to 2.61 times, compared to the untreated soils. Our results indicate that growing vegetables in soils near CCA-treated wood may pose a risk of As exposure for humans. Compost amendment can reduce such a risk by reducing As accumulation by vegetables and can be an important strategy for remediating CCA-contaminated soils. Caution should be taken for phosphate application since it enhances As accumulation.