μM AsIII Research Articles

Untying arsenite tolerance mechanisms in contrasting maize genotypes attributed to NIPs-mediated controlled influx and root-to-shoot translocation, redox homeostasis and phytochelatin-mediated detoxification pathway

Contamination of ground water and soil with toxic metalloids like arsenic (As) poses a serious hazard to the global agricultural food production. One of the best ways to restrict entry of As into the food chain is selection of germplasms which accrue extremely low level of As in grains. Here, we screened diverse maize genotypes under high arsenite (100 μM AsIII) stress and identified PMI-PV-9 and PMI-PV-3 as AsIII-tolerant and -sensitive maize genotype respectively. Expression of genes associated with As uptake, vacuolar sequestration, biosynthesis of phytochelatins, root-to-shoot translocation, in vivo ROS generation, fine tuning of antioxidant defense system, DNA and membrane damage, H2O2 and superoxide anion (O2•-) levels were compared among the selected genotypes. PMI-PV-9 plants performed much better than PMI-PV-3 in terms of plant growth with no visible symptom of As toxicity. Susceptibility of PMI-PV-3 to AsIII stress may be attributed to comparatively low expression of genes involved in phytochelatins (PCs) biosynthesis. Concomitant decrease in ABCC1 expression might be another key factor for futile sequestration of AsIII into root vacuoles. Moreover, up-regulation of ZmNIP3;1 might contribute in high root-to-leaf As translocation. Substantial spike in H2O2, O2•- and MDA levels indicates that PMI-PV-3 plants have experienced more oxidative stress than PMI-PV-9 plants. Appearance of prominent deep brown and dark blue spots/stripes on leaves as revealed after DAB and NBT staining respectively suggest severe oxidative burst in PMI-PV-3 plants. Marked reduction in DHAR and MDAR activity rendered PMI-PV-3 cells to recycle ascorbate pool ineffectively, which might have exacerbated their susceptibility to AsIII stress. In a nutshell, incompetent PCs mediated detoxification system and disruption of cellular redox homeostasis owing to feeble antioxidant defence system resulting oxidative burst might be the prime reasons behind reduced performance of PMI-PV-3 plants under AsIII stress.

Arsenite Antiporter PvACR3 Driven by Its Native Promoter Increases Leaf Arsenic Accumulation in Tobacco.

Pteris vittata is the first-reported arsenic (As) hyperaccumulator, which has been applied to phytoremediation of As-contaminated soil. PvACR3, a key arsenite (AsIII) antiporter, plays an important role in As hyperaccumulation in P. vittata. However, its functions in plants are not fully understood. In this study, the PvACR3 gene was heterologously expressed in tobacco, driven by its native promoter (ProPvACR3). After growing at 5 μM AsIII or 10 μM AsV in hydroponics for 1-5 days, PvACR3-expression enhanced the As levels in leaves by 66.4-113 and 51.8-101%, without impacting the As contents in the roots or stems. When cultivated in As-contaminated soil, PvACR3-expressed transgenic plants accumulated 47.9-85.5% greater As in the leaves than wild-type plants. In addition, PvACR3-expression increased the As resistance in transgenic tobacco, showing that enhanced leaf As levels are not detrimental to its overall As tolerance. PvACR3 was mainly expressed in tobacco leaf veins and was likely to unload AsIII from the vein xylem vessels to the mesophyll cells, thus elevating the leaf As levels. This work demonstrates that heterologously expressing PvACR3 under its native promoter specifically enhances leaf As accumulation in tobacco, which helps to reveal the As-hyperaccumulation mechanism in P. vittata and to enhance the As accumulation in plant leaves for phytoremediation.

Green synthesis of iron oxide nanoparticles and their ameliorative effect on arsenic stress relief in Oryza sativa seedlings

Nanotechnology has immense potential in the field of agriculture. This study utilized an eco-friendly method to synthesize iron oxide nanoparticles (FeO-NPs) using leaf extract of Adiantum lunulatum. The synthesized FeO-NPs were characterized by UV–visible spectroscopy, FTIR, zeta potential, XRD, EDX and TEM analysis. The nanoparticles were quasi-spherical, with a mean particle size of 5 ± 1 nm (range: 3–10 nm). The 100 mg/L dose of FeO-NPs was further applied in the rice growth medium to check the effect of FeO-NPs on the growth of rice seedlings against arsenic (As) stress. FeO-NPs significantly improved seed germination by 9.8% and 15.4%, respectively, of seeds germinated under 50 μm AsIII and 50 μm AsV stress when compared to seed germinated in only 50 μm AsIII and 50 μm AsV. The phytotoxic effect of AsIII on seed germination, seedling growth, chlorophyll content was more severe than AsV. However, IONP fertigation helps the rice plants to overcome the detrimental effect caused by As exposure. FeO-NPs increased the growth and vigour of the seedlings under As stress. The uptake and translocation of As by seedlings were decreased with IONP fertigation under As stress. The reduced accumulation of As in seedlings treated with FeO-NPs caused a significant (p ≤ 0.05) reduction in oxidative stress and antioxidants activities. All these findings indicated that the synthesis of FeO-NPs using Adiantum lunulatum leaf extract not only produces safe and non-toxic FeO-NPs but these FeO-NPs can be also efficiently improve the rice seedling growth under As stressed condition.

Rice seed (IR64) priming with potassium humate for improvement of seed germination, seedling growth and antioxidant defense system under arsenic stress

The intolerable levels of arsenic (As) in groundwater and its application in rice cultivation are continuously affecting the rice production in Ganga-Meghna-Brahmaputra (GMB) plain. The reduced germination and plant growth rates under excessive As stress ultimately lead to lower yield. To mitigate this concerning issue, the present study was carried out to evaluate the potential of K-humate priming on seed germination and plant growth under As stress. Seeds were primed with 100 mg/l K-humate for 12 h prior to germination. The germination percentages in unprimed seeds were 65 ± 5.0% and 58.3 ± 7.6% under stress level of 50 μM AsV and 50 μM AsIII, respectively. However, germination percentage in K-humate primed seeds were 75 ± 5.0% and 68.3 ± 2.9% under AsV and AsIII stress, respectively. The vigour index I (VG I) and vigour index II (VG II) recorded on 12 DAS (days after seeding) were also increased by 1.47 and 1.51 fold, respectively with K-humate supplementation under As stress. Detrimental effects of AsIII on seed germination, seedling growth and other physiological parameters were more suppressive than AsV. Application of K-humate not only improved seed germination, seedling growth and nutrient uptake but also decreased the oxidative stress markers and antioxidant activities by minimizing As uptake and translocation in the seedlings.

Selenide stimulates the biliary excretion of arsenic in human HepaRG cells

Arsenic is classified by the International Agency for Research on Cancer as a Group I (proven) human carcinogen causing lung, skin and bladder cancer. Conservative estimates suggest that between 92-220 million people worldwide are exposed to arsenic at levels exceeding the World Health Organization guideline of 10 µg/L. In animal models arsenic and selenium are mutually protective via the formation and biliary excretion of the seleno-bis (S-glutathionyl) arsinium ion [SeAs(GS)2]-, which allows for the fecal elimination of both compounds. Consistent with this, selenium deficiency in humans living in arsenic endemic regions is associated with an increased risk of arsenic induced disease. These observations have led to the initiation of human selenium supplementation trials. Despite these ongoing trials in arsenic endemic regions, the influence of selenium on human hepatic handling of arsenic is not adequately understood. Furthermore, supplementation trials have utilized different chemical forms of selenium with unknown influence on efficacy. In the liver, multidrug resistance protein 2 (MRP2/ABCC2) transports arsenic metabolites, including [SeAs(GS)2]-into bile, and the related MRP4 (ABCC4) transports other arsenic metabolites into hepatic sinusoids. We hypothesized that selenium increases biliary excretion of arsenite (AsIII) from HepaRG cells, an immortalized cell line used as a surrogate for primary human hepatocytes. Our objective was to study the influence of selenite (SeIV), selenide (HSe-), methylselenocysteine (MeSeCys) and selenomethionine (SeMet) on arsenic efflux from HepaRG cells. HepaRG cells were untreated, or treated with 1 µM AsIII ± selenium (SeIV, HSe-, MeSeCys or SeMet) for 48 hr. Then crude membrane preparations of HepaRG cells were subjected to immunoblots to evaluate the presence of MRP2 and MRP4 proteins. MRP2 function was evaluated by 5(6)-carboxy,2’,7’ dichlorofluorescein (CDF) accumulation in canalicular networks by fluorescence microscopy. Transport across sinusoidal and canalicular membranes was measured after treatment of HepaRG cells with 1 µM 73AsIII ± selenium (SeIV, HSe-, MeSeCys or SeMet) using B-CLEAR® technology. Biliary excretion indices (BEIs) were calculated to quantify the extent of arsenic export into bile. Transport was re-evaluated under conditions expected to inhibit efflux. MRP2 and MRP4 proteins are present in HepaRG cells. MRP2 levels increased after treatment with AsIII ± HSe-, whereas MRP4 levels increased after treatment with 1 µM AsIII. CDF accumulated in canalicular networks, suggesting the presence of functional MRP2. At a 5 minute time point, the BEI of 73AsIII alone was 13±7%, which was stimulated by the presence of HSe- (BEI=31±7%). Biliary excretion of 73AsIII was lost in the presence of other selenium forms, but sinusoidal efflux of 73AsIII was stimulated by MeSeCys. Reduction of hepatobiliary transport was observed at 4∘C as well as with inhibitors of glutathione synthesis and MRPs. Arsenic underwent biliary excretion in HepaRG cells, and this was stimulated by HSe-, the biologically active form of selenium metabolism. Arsenic hepatobiliary transport by MRP2 is temperature and glutathione dependent. This work advances understanding of selenium effects on arsenic handling by human liver.

Novel PvACR3;2 and PvACR3;3 genes from arsenic-hyperaccumulator Pteris vittata and their roles in manipulating plant arsenic accumulation

Arsenite (AsIII) antiporter ACR3 is crucial for arsenic (As) translocation and sequestration in As-hyperaccumulator Pteris vittata, which has potential for phytoremediation of As-contaminated soils. In this study, two new ACR3 genes PvACR3;2 and PvACR3;3 were cloned from P. vittata and studied in model organism yeast (Saccharomyces cerevisiae) and model plant tobacco (Nicotiana tabacum). Both ACR3s mediated AsIII efflux in yeast, decreasing its As accumulation and enhancing its As tolerance. In addition, PvACR3;2 and PvACR3;3 were expressed in tobacco plant. Localized on the plasma membrane, PvACR3;2 mediated both AsIII translocation to the shoots and AsIII efflux from the roots in tobacco, resulting in 203 − 258% increase in shoot As after exposing to 5 μM AsIII under hydroponics. In comparison, localized to the vacuolar membrane, PvACR3;3 sequestrated AsIII in tobacco root vacuoles, leading to 18 − 20% higher As in the roots and 15 − 36% lower As in the shoots. Further, based on qRT-PCR, both genes were mainly expressed in P. vittata fronds, indicating PvACR3;2 and PvACR3;3 may play roles in AsIII translocation and sequestration in the fronds. This study provides not only new insights into the functions of new ACR3 genes in P. vittata, but also important gene resources for manipulating As accumulation in plants for phytoremediation and food safety.

The role of melatonin in reinforcement of antioxidant system of rice plant (Oryza sativa L.) under arsenite toxicity?

Arsenic (As) is a toxic metalloid, which enters into the human food chain mainly through rice. One imminent toxic effect of As is oxidative stress. Melatonin is potentially an antioxidant compound. The aim of the present study was to evaluate the efficiency of melatonin to decrease arsenite (AsIII) toxicity in rice (Oryza sativa L.). Twenty one day old rice plants were treated with or without 25 µM AsIII, 0.25 µM melatonin, and a combination of both, for 48 h in hydroponic culture. Arsenite toxicity was manifested as reduced chlorophyll, soluble sugars and protein contents, and decreased growth of the plants (48%, 29.1%, 23.6% and 87.5% of the controls, respectively). In addition, AsIII increased the content of H2O2, the activity of catalase (CAT), the contents of total non-protein thiols (TNP-SH), glutathione (GSH), and phytochelatine (PCs) (2.5%, 926%, 191.5%, 12.3% and 361.4 of their corresponding controls, respectively). In the presence of AsIII, however, melatonin ameliorated oxidative stress on roots by reducing As content, increasing the contents of TNP-SH, GSH, and PCs which led to decrease of H2O2 and malondialdehyde (MDA) content. The results also indicated that melatonin facilitated the transportation of As from roots to shoots, resulting in turn in higher accumulation of As in shoots and suppression of antioxidant system. Further studies are needed in order to clarify the mechanism(s) by which melatonin accelerated transportation of As from root to shoot of rice plant.

Exogenous application of methyl jasmonate alleviates arsenic toxicity by modulating its uptake and translocation in rice (Oryza sativa L.)

Methyl jasmonate (Me-JA) is a plant growth regulator known for modulating plant responses to various abiotic and biotic stresses. The unavoidable arsenic (As) contamination in rice (Oryza sativa) results in reduced crop yield and greater carcinogenic risk to humans. The present work examines the significance of Me-JA induced molecular signaling and tolerance towards arsenic toxicity in rice. The arsenite (AsIII; 25μM) stress hampered the overall growth and development of the rice seedling. However, the co-application (25μM AsIII+0.25μM Me-JA) resulted in increased biomass, chlorophyll content, enhanced antioxidant enzyme activities as compared to AsIII treated plants. The co-application also demonstrated a marked decrease in malondialdehyde content, electrolyte leakage and accumulation of total AsIII content (root+shoot) as compared to AsIII treated plants. The co-application also modulated the expression of genes involved in downstream JA signaling pathway (OsCOI, OsJAZ3, OsMYC2), AsIII uptake (OsLsi1, OsLsi2, OsNIP1;1, OsNIP3;1), translocation (OsLsi6, and OsINT5) and detoxification (OsNRAMP1, OsPCS2, and OsABCC2) which revealed the probable adaptive response of the rice plant to cope up arsenic stress. Our findings reveal that Me-JA alleviates AsIII toxicity by modulating signaling components involved in As uptake, translocation, and detoxification and JA signaling in rice. This study augments our knowledge for the future use of Me-JA in improving tolerance against AsIII stress.

Involvement of glutathione and glutathione metabolizing enzymes in Pistia stratiotes tolerance to arsenite

Glutathione is essential for plant tolerance to arsenic but few studies have focused on the coordination between the enzymes involved in its metabolism. We exposed Pistia stratiotes to four treatments (control, 5, 10 and 20 µM AsIII) for 24 h to evaluate the role of glutathione metabolism in arsenic response and determined the arsenic uptake, growth, membrane integrity, glutathione concentration and enzyme activities (γ-glutamyl-cysteine synthetase, glutathione reductase, glutathione peroxidase, and glutathione-S-transferase). Despite absorbing high concentrations of AsIII, plants maintained growth and cell membrane integrity when exposed to concentrations of up to 10 µM AsIII. The maintenance of these parameters involved glutathione concentration increase due to an increase in its biosynthetic pathway (higher γ-glutamyl-cysteine synthetase). In addition, an increase in the activity of glutathione reductase, glutathione peroxidase and glutathione-S-transferase also contributed to the conserve the cellular homeostasis. However, at the concentration of 20 µM AsIII, the high toxicity of AsIII affected glutathione concentration and glutathione metabolizing enzymes activities, which resulted in drastic decrease in growth and damage to cell membranes. These results showed that not only the glutathione concentration but also the coordination of the enzymes involved in the synthesis, oxidation and reduction pathways of glutathione is essential for AsIII tolerance.

Phytoremediation of arsenite-contaminated environments: is Pistia stratiotes L. a useful tool?

Abstract Phytoremediation is considered an ecologically beneficial technique for removing arsenic from aquatic environments but studies on the mechanisms of tolerance to this pollutant, when present in the form of arsenite (AsIII) still need to be performed. Thus, in order to evaluate the potential of Pistia stratiotes to phytoremediation of AsIII and the morphological and biochemical responses involved in metalloid tolerance, P. stratiotes plants were exposed to four treatments: 0 (control), 5, 10 and 20 µM AsIII, remaining under treatment for 24 h for biochemical analysis and for 4 days to analyze the arsenic (As) uptake, biomass production, bioconcentration factor (BCF), translocation factor (TF) and visual symptomatology. The plants were able to accumulate As in both roots and leaves. This accumulation was higher in the treatment with 10 µM AsIII (1120.40 and 31.60 µg g−1 dry weight in roots and leaves, respectively), decreasing in the following concentration. P. stratiotes also showed a high BCF, that was higher than 1000 when exposed to 5 and 10 µM AsIII (1808.38 and 1536.02, respectively). The pollutant was maintained mainly at the root (TF was always lower than 1.0) which may be a defense mechanism of aquatic plants to As. Despite the significant accumulation of pollutant, the plants were able to maintain growth in all evaluated concentrations, although in very different proportions. In fact, while in the lower concentration of As the biomass production was not affected, in the treatment with 20 μM AsIII the dry biomass decreased in approximately 77%. The accumulation of As resulted in the appearance of visual symptoms of toxicity such as chlorosis, darkening and reduction of the root system, which were more conspicuous in the highest As concentration. The metalloid exposition also triggered biochemical alterations, increasing the membrane damage and the reactive oxygen species (ROS) levels and, once again, these damages were more intense in the plants exposed to 20 μM AsIII. The action of the antioxidant system (especially in the leaves) and the compartmentalization of the pollutant in the root system apparently was important in the P. stratiotes response to toxic compounds and allowed the plants to maintain the cell homeostasis and the growth at the two lowest As concentrations. Thus, the data suggest that P. stratiotes may has a potential for phytoremediation of aquatic environments contaminated with AsIII concentrations close to 10 µM.

Phytoremediation potential of Salvinia molesta for arsenite contaminated water: role of antioxidant enzymes

Antioxidant enzymes are important components in the defense against arsenic (As) stress in plants. Here, we tested the hypothesis that Salvinia molesta, an aquatic fern, counteracts the harmful arsenite (AsIII) effects by activating scavenging reactive oxygen species (ROS) enzymes. Thus, our objective was to investigate the role of the superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), and ascorbate peroxidase (APX) in S. molesta tolerance to AsIII and indicate the use of this plant in remediation of contaminated water. Plants were grown in nutrient solution at pH 6.5 and exposed to 0, 5, 10, or 20 µM AsIII for 96 h (analyses of As absorption, mineral nutrient content, and relative growth rate) and for 24 h (analyses of oxidative stress indicators and enzymatic antioxidant defenses). In the floating leaves, there was a greater basal activity of the antioxidant enzymes and less accumulation of As than in submerged leaves. The submerged leaves, which function as roots in S. molesta, accumulated more As than floating leaves, and SOD and CAT activities were inhibited. Thus, there was a greater production of ROS and oxidative stress. Our results show that S. molesta presents enzymatic antioxidant defenses to alleviate AsIII toxicity and are more effectives in the floating leaves. These results are important to elucidate the AsIII tolerance mechanisms in S. molesta and the possibility of their use in contamined water phytoremediation. Additional studies exposing plants to more prolonged stress and using AsIII concentrations closer to those found in contaminated environments will confirm this claim.

Differential responses of two Iranian rice cultivars to arsenite toxicity

Arsenic (As) is a toxic metalloid which is usually found in rice fields as a contamination and has negative effects on the plant growth and reduces the crop yield. Similar to heavy metals, the deleterious effects of As may be due to, at least in part, the amount of absorbed As and disturbance of the plant water status. In this connection, different varieties of the same species may show differential performances. Comparative responses to 75 µM AsIII were evaluated in two Iranian rice cultivars adapted to moderate-humid vs. very warm and dry climates (Hashemi and Amber, respectively). Although both cultivars absorbed AsIII, but its translocation factor was lower in Amber accompanied by accumulation of soluble sugars and glycine betaine and lower level of internal ABA. Moreover, adverse effect of AsIII onrelative water content and stomata closure was less prominent in Amber, compared to Hashemi. Results suggest that cultivars adapted to dry conditions are more capable to withstand against As and to control its entrance to human food chain.

Heterologous Expression of Pteris vittata Arsenite Antiporter PvACR3;1 Reduces Arsenic Accumulation in Plant Shoots.

Arsenic (As) is a toxic carcinogen so it is crucial to decrease As accumulation in crops to reduce its risk to human health. Arsenite (AsIII) antiporter ACR3 protein is critical for As metabolism in organisms, but it is lost in flowering plants. Here, a novel ACR3gene from As-hyperaccumulator Pteris vittata, PvACR3;1, was cloned and expressed in Saccharomyces cerevisiae (yeast), Arabidopsis thaliana (model plant), and Nicotiana tabacum (tobacco). Yeast experiments showed that PvACR3;1 functioned as an AsIII-antiporter to mediate AsIII efflux to an external medium. At 5 μM AsIII, PvACR3;1 transgenic Arabidopsis accumulated 14-29% higher As in the roots and 55-61% lower As in the shoots compared to WT control, showing lower As translocation. Besides, transgenic tobacco under 5 μM AsIII or AsV also showed similar results, indicating that expressing PvACR3;1gene increased As retention in plant roots. Moreover, observation of PvACR3;1-green fluorescent protein fusions in transgenic Arabidopsis showed that PvACR3;1 protein localized to the vacuolar membrane, indicating that PvACR3;1 mediated AsIII sequestration into vacuoles, consistent with increased root As. In addition, soil experiments showed ∼22% lower As in the shoots of transgenic tobacco than control. Thus, our study provides a potential strategy to limit As accumulation in plant shoots, representing the first report to decrease As translocation by sequestrating AsIII into vacuoles, shedding light on engineering low-As crops to improve food safety.

Arsenite and arsenate impact the oxidative status and antioxidant responses in Ocimum tenuiflorum L.

Biochemical responses of Ocimum tenuiflorum plants were studied upon exposure to arsenite (AsIII) and arsenate (AsV) for 1 to 10d. Plants accumulated significant amounts of As in leaves (662μgg(-1) dry weight; DW and 412μgg(-1) DW in response to 100μM AsIII and AsV exposure, respectively after 10d). Consequently, fresh weight and growth of plants declined in a concentration dependent manner. Further, total chlorophyll and carotenoid contents also declined while oxidative stress markers increased, particularly on longer durations. Various antioxidant enzymes and thiols (cysteine and glutathione; GSH) showed significant and variable increases upon exposure to AsV and AsIII with the response being comparatively better in response to AsV. Proline increased significantly upon exposure to both AsIII and AsV. Plants thus tolerated high As concentrations through induced antioxidant machinery.

A periplasmic arsenite‐binding protein involved in regulating arsenite oxidation

Arsenic (As) is the most common toxic element in the environment, ranking first on the Superfund List of Hazardous Substances. Microbial redox transformations are the principal drivers of As chemical speciation, which in turn dictates As mobility and toxicity. Consequently, in order to manage or remediate environmental As, land managers need to understand how and why microorganisms react to As. Studies have demonstrated a two-component signal transduction system comprised of AioS (sensor kinase) and AioR (response regulator) is involved in regulating microbial AsIII oxidation, with the AsIII oxidase structural genes aioB and aioA being upregulated by AsIII. However, it is not known whether AsIII is first detected directly by AioS or by an intermediate. Herein we demonstrate the essential role of a periplasmic AsIII-binding protein encoded by aioX, which is upregulated by AsIII. An ΔaioX mutant is defective for upregulation of the aioBA genes and consequently AsIII oxidation. Purified AioX expressed without its TAT-type signal peptide behaves as a monomer (MW 32 kDa), and Western blots show AioX to be exclusively associated with the cytoplasmic membrane. AioX binds AsIII with a K(D) of 2.4 µM AsIII; however, mutating a conserved Cys108 to either alanine or serine resulted in lack of AsIII binding, lack of aioBA induction, and correlated with a negative AsIII oxidation phenotype. The discovery and characterization of AioX illustrates a novel AsIII sensing mechanism that appears to be used in a range of bacteria and also provides one of the first examples of a bacterial signal anchor protein.

Uptake and translocation of arsenite and arsenate by Pteris vittata L.: Effects of silicon, boron and mercury

To better understand arsenite (AsIII) uptake via aquaporin channels by arsenic hyperaccumulator Pteris vittata, the effects of silicic and boric acid (AsIII analogues) and HgCl 2 (aquaporin inhibitor) on plant arsenic uptake and translocation were investigated. P. vittata was grown in 0.2-strength Hoagland solution containing (1) 15 μM AsIII or arsenate (AsV) for 1 d with or without 0.5 mM silicic acid (Si experiment) or 0.3 mM boric acid (B experiment), or (2) 15 μM AsIII for 2 d with or without 10 μM HgCl 2 (Hg experiment). Silicic acid and boric acid had no effect on AsIII and AsV uptake by P. vittata, nor did HgCl 2. It is possible that AsIII was taken up by different aquaporins in P. vittata or those aquaporins in P. vittata had high capacity and they were insensitive to Hg. While AsV was stable in the growth media, substantial amount of AsIII was oxidized to AsV, i.e., 16–76%. In the presence of 210 μM P at pH 6, P. vittata was more efficient in taking up and translocating AsIII than AsV as demonstrated by greater arsenic concentrations in the fronds and roots (6.6 and 46 mg kg −1) in the AsIII treatment than those in the AsV treatment (2.3 and 8.2 mg kg −1). However, at 15 μM AsIII, its AsIII translocation rate from the roots to the fronds was slower than its AsIII uptake rate by the roots since the arsenic concentration in the fronds was only ∼14% of that in the roots. Our data also demonstrated that both AsIII oxidation and AsV reduction occurred in the roots of P. vittata. However, how and if AsIII uptake by P. vittata is via aquaporins still need further investigation.