Arsenic-induced nutrient uptake in As-hyperaccumulator Pteris vittata and their potential role to enhance plant growth

Novel Phosphate Transporter-B PvPTB1;1/1;2 Contribute to Efficient Phosphate Uptake and Arsenic Accumulation in As-Hyperaccumulator Pteris vittata

Arsenic (As) contamination in soil poses a potential threat to human health via crop uptake. As-hyperaccumulator Pteris vittata serves as a model plant to study As uptake and associated mechanisms. This study focuses on a novel P/AsV transport system mediated by low-affinity phosphate transporter-B 1 family (PTB1) in P. vittata. Here, we identified two plasma-membrane-localized PTB1 genes, PvPTB1;1/1;2, in vascular plants for the first time, which were 4.4-40-fold greater in expression in P. vittata than in other Pteris ferns. Functional complementation of a yeast P-uptake mutant and enhanced P accumulation in transgenic Arabidopsis thaliana confirmed their role in P uptake. Moreover, the expression of PvPTB1;1/1;2 facilitated the transport and accumulation of As in both yeast and A. thaliana shoots, demonstrating a comparable AsV uptake capacity. Microdissection-qPCR analysis and single-cell transcriptome analysis collectively suggest that PvPTB1;1/1;2 are specifically expressed in the epidermal cells of P. vittata roots. PTB1 may play a pivotal role in efficient P recycling during phytate secretion and hydrolysis in P. vittata roots. In summary, the dual P transport mechanisms consisting of high-affinity Pht1 and low-affinity PTB1 may have contributed to the efficient P/As uptake in P. vittata, thereby contributing to efficient phytoremediation for As-contaminated soils.

Insoluble-Phytate Improves Plant Growth and Arsenic Accumulation in As-Hyperaccumulator Pteris vittata: Phytase Activity, Nutrient Uptake, and As-Metabolism

Phytate, the principal P storage in plant seeds, is also an important organic P in soils, but it is unavailable for plant uptake. However, the As-hyperaccumulator Pteris vittata can effectively utilize soluble Na-phytate, while its ability to utilize insoluble Ca/Fe-phytate is unclear. Here, we investigated phytate uptake and the underlying mechanisms based on the phytase activity, nutrient uptake, and expression of genes involved in As metabolisms. P. vittata plants were cultivated hydroponically in 0.2-strength Hoagland nutrient solution containing 50 μM As and 0.2 mM Na/Ca/Fe-phytate, with 0.2 mM soluble-P as the control. As the sole P source, all three phytates supported P. vittata growth, with its biomass being 3.2-4.1 g plant-1 and Ca/Fe-phytate being 19-29% more effective than Na-phytate. Phytate supplied soluble P to P. vittata probably via phytase hydrolysis, which was supported by 0.4-0.7 nmol P min-1 g-1 root fresh weight day-1 phytase activity in its root exudates, with 29-545 μM phytate-P being released into the growth media. Besides, compared to Na-phytate, Ca/Fe-phytate enhanced the As contents by 102-140% to 657-781 mg kg-1 in P. vittata roots and by 43-86% to 1109-1447 mg kg-1 in the fronds, which was accompanied by 21-108% increase in Ca and Fe uptake. The increased plant As is probably attributed to 1.3-2.6 fold upregulation of P transporters PvPht1;3/4 for root As uptake, and 1.8-4.3 fold upregulation of arsenite antiporters PvACR3/3;1/3;3 for As translocation to and As sequestration into the fronds. This is the first report to show that, besides soluble Na-phytate, P. vittata can also effectively utilize insoluble Ca/Fe-phytate as the sole P source, which sheds light onto improving its application in phytoremediation of As-contaminated sites.

N-acetyl-cysteine mitigates arsenic stress in lettuce: Molecular, biochemical, and physiological perspective

Agricultural land contaminated with heavy metals such as non-biodegradable arsenic (As) has become a serious global problem as it adversely affects agricultural productivity, food security and human health. Therefore, in this study, we investigated how the administration of N-acetyl-cysteine (NAC), regulates the physio-biochemical and gene expression level to reduce As toxicity in lettuce. According to our results, different NAC levels (125, 250 and 500 μM) significantly alleviated the growth inhibition and toxicity induced by As stress (20 mg/L). Shoot fresh weight, root fresh weight, shoot dry weight and root dry weight (33.05%, 55.34%, 17.97% and 46.20%, respectively) were decreased in plants grown in As-contaminated soils compared to lettuce plants grown in soils without the addition of As. However, NAC applications together with As stress increased these growth parameters. While the highest increase in shoot fresh and dry weight (58.31% and 37.85%, respectively) was observed in 250 μM NAC application, the highest increase in root fresh and dry weight (75.97% and 63.07%, respectively) was observed in 125 μM NAC application in plants grown in As-polluted soils. NAC application decreased the amount of ROS, MDA and H2O2 that increased with As stress, and decreased oxidative damage by regulating hormone levels, antioxidant and enzymes involved in nitrogen metabolism. According to gene expression profiles, LsHIPP28 and LsABC3 genes have shown important roles in reducing As toxicity in leaves. This study will provide insight for future studies on how NAC applications develop resistance to As stress in lettuce.

Characterization of an antimony-resistant fungus Sarocladium kiliense ZJ-1 and its potential as an antimony bio-remediator

Antimony (Sb) is a toxic metalloid widely distributed in the natural environments. Microorganisms, especially fungi, could serve as ideal biomaterials for bioremediation of Sb-polluted soils and waters. In this study, we isolated an antimony-resistant fungus, Sarocladium kiliense ZJ-1, from a slag sample collected in Xikuangshan Sb mine in P. R. China. ZJ-1 showed an extremely high resistance to Sb, with a MIC level of > 175 mM for arsenite [Sb(Ⅲ)] and 40 mM for arsenate [Sb(V)]. Whole genomic analysis identified multiple Sb (Ⅲ)- and/or As(Ⅲ)-resistant genes on ZJ-1's genome, which may partially explain its hyper-resistance to Sb. The potential of ZJ-1 in removing Sb from Sb(Ⅲ) or Sb(V) solutions was also quantified. The average biosorption capacity of ZJ-1 for Sb(Ⅲ) and Sb(V) is 635.14 mg/g and 149.65 mg/g, respectively, in Sb aqueous solutions with an initial concentration of 2000 mg/L (16.43 mM). Besides, almost 99% of Sb(Ⅲ) in the growing system was removed with an initial concentration of 500 mg/L (4.11 mM). Furthermore, Fourier transformation infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) were used to probe the Sb adsorption mechanism on ZJ-1, and -OH, -NH2, -COOH, C-O and C-O-C were found to be the main surface functional groups of ZJ-1 cells to adsorb Sb.

Arsenic in the hyperaccumulator Pteris vittata: A review of benefits, toxicity, and metabolism

Arsenic (As) is a toxic metalloid, elevated levels of which in soils are becoming a major global environmental issue that poses potential health risks to humans. Pteris vittata, the first known As hyperaccumulator, has been successfully used to remediate As-polluted soils. Understanding why and how P. vittata hyperaccumulates As is the core theoretical basis of As phytoremediation technology. In this review, we highlight the beneficial effects of As in P. vittata, including growth promotion, elemental defense, and other potential benefits. The stimulated growth of P. vittata induced by As can be defined as As hormesis, but differs from that in non-hyperaccumulators in some aspects. Furthermore, the As coping mechanisms of P. vittata, including As uptake, reduction, efflux, translocation, and sequestration/detoxification are discussed. We hypothesize that P. vittata has evolved strong As uptake and translocation capacities to obtain beneficial effects from As, which gradually leads to As accumulation. During this process, P. vittata has developed a strong As vacuolar sequestration ability to detoxify overloaded As, which enables it to accumulate extremely high As concentrations in its fronds. This review also provides insights into several important research gaps that need to be addressed to advance our understanding of As hyperaccumulation in P. vittata from the perspective of the benefits of As.

The influence of diverse fertilizer regimes on the phytoremediation potential of Pteris vittata in an abandoned nonferrous metallic mining site

Organic waste comprises a large amount of hydrocarbon containing organic substances, which is regarded as a potential resource rather than simply a waste. A field experiment was conducted in a poly-metallic mining area to investigate the potential of organic waste to facilitate the soil remediation process. Different organic wastes and a commonly used commercial fertilizer were added to heavy metal contaminated soil, which was under phytoremediation using the As hyperaccumulator Pteris vittata. The influence of diverse fertilizer regimes on the biomass of P. vittata and heavy metal removal by P. vittata, was investigated. The soil properties were analyzed after the application of phytoremediation with or without the addition of organic wastes. Results indicated that sewage sludge compost is an appropriate amendment to improve the phytoremediation efficiency. Compared to the control, the application of sewage sludge compost significantly reduced the extractability of As in soil by 26.8 %, and increased the removal of As and Pb by 26.9 % and 186.5 %, respectively. The highest removal of As and Pb reached 33 and 34 kg/ha, respectively. The sewage sludge compost-strengthened phytoremediation improved soil quality. And the diversity and richness of the bacterial community were improved, as represented by the increase in Shannon and Chao index. With improved efficiency and acceptable cost, the organic waste-strengthened phytoremediation can be used to control the risks posed by high concentrations of heavy metals in mining areas.

New insights in to the ameliorative effects of zinc and iron oxide nanoparticles to arsenic stressed spinach (Spinacia oleracea L.)

Nanotechnology is capturing great interest worldwide due to their stirring applications in various fields and also individual application of iron oxide nanoparticle (FeO-NPs) and zinc oxide nanoparticle (ZnO-NPs) have been studied in many literatures. However, the combined application of FeO and ZnO-NPs is a novel approach and studied in only few studies. For this purpose, a pot experiment was conducted to examine the plant growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress and response of antioxidant compounds (enzymatic and nonenzymatic), sugars, nutritional status of the plant, organic acid exudation pattern As accumulation from the different parts of the plants in spinach (Spinacia oleracea L.) under the different As concentrations i.e., 0 (no As), 60 and 120 μM] which were primed with combined application of two levels of FeO-NPs (10 and 20 mg L^-1) and ZnO-NPs (20 and 40 mg L^-1). Results from the present study showed that the increasing levels of As in the soil significantly (P < 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants. In contrast, increasing levels of As in the soil significantly (P < 0.05) increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, and also increased organic acid exudation patter in the roots of S. oleracea. The negative impact of As toxicity can overcome the combined application of ZnO-NPs and FeO-NPs, which ultimately increased plant growth and biomass by capturing the reactive oxygen species, and decreased oxidative stress in S. oleracea by decreasing the As contents in the roots and shoots of the plants. Research findings, therefore, suggest that the combined application of ZnO-NPs and FeO-NPs can ameliorate As toxicity in S. oleracea, resulting in improved plant growth and composition under As stress, as depicted by balanced exudation of organic acids.

Arsenic induced plant growth by increasing its nutrient uptake in As-hyperaccumulator Pteris vittata: Comparison of arsenate and arsenite

Arsenic-hyperaccumulator Pteris vittata is efficient in taking up arsenate (AsV) and arsenite (AsIII), however, their impacts on P. vittata growth and nutrient uptake remain unclear. The uptake of AsV and AsIII, their influences on nutrient uptake and plant biomass, and As speciation were investigated in P. vittata after exposing to 5 or 50 μM AsV or AsIII for 12 d under hydroponics. The results show that AsV uptake in P. vittata was 1.2 times more efficient than AsIII, corresponding to 1.7-2.1 fold greater biomass than the control at 50 μM As. While AsV was dominant in the roots at ∼60%, AsIII was more dominant in the fronds at ∼70% in all treatments. Macronutrients P, K, Ca, and S were increased by 118-185% at 50 μM As, with greater uptake of micronutrients Fe, Mn, Cu, and Zn at 5 μM As. Further, positive correlations between P. vittata biomass and its As contents (r = 0.97), and P. vittata biomass and its S, Mg, P, or Ca contents (r = 0.70-0.98) were observed. Our results suggest that its increased nutrient uptake probably enhanced P. vittata growth under As exposure.

Combined application of plant growth-promoting bacteria and iron oxide nanoparticles ameliorates the toxic effects of arsenic in Ajwain (Trachyspermum ammi L.)

Soil contamination with toxic heavy metals [such as arsenic (As)] is becoming a serious global problem because of the rapid development of the social economy. Although plant growth-promoting bacteria (PGPB) and nanoparticles (NPs) are the major protectants to alleviate metal toxicity, the study of these chemicals in combination to ameliorate the toxic effects of As is limited. Therefore, the present study was conducted to investigate the combined effects of different levels of Providencia vermicola (5 ppm and 10 ppm) and iron oxide nanoparticles (FeO-NPs) (50 mg/l^-1 and 100 mg/l^-1) on plant growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress and response of antioxidant compounds (enzymatic and non-enzymatic), and their specific gene expression, sugars, nutritional status of the plant, organic acid exudation pattern As accumulation from the different parts of the plants, and electron microscopy under the soil, which was spiked with different levels of As [0 μM (i.e., no As), 50 μM, and 100 μM] in Ajwain (Trachyspermum ammi L.) seedlings. Results from the present study showed that the increasing levels of As in the soil significantly (p< 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants, and destroyed the ultra-structure of membrane-bound organelles. In contrast, increasing levels of As in the soil significantly (p< 0.05) increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, and also increased organic acid exudation patter in the roots of T. ammi seedlings. The negative impact of As toxicity can overcome the application of PGPB (P. vermicola) and FeO-NPs, which ultimately increased plant growth and biomass by capturing the reactive oxygen species, and decreased oxidative stress in T. ammi seedlings by decreasing the As contents in the roots and shoots of the plants. Our results also showed that the FeO-NPs were more sever and showed better results when we compared with PGPB (P. vermicola) under the same treatment of As in the soil. Research findings, therefore, suggest that the combined application of P. vermicola and FeO-NPs can ameliorate As toxicity in T. ammi seedlings, resulting in improved plant growth and composition under metal stress, as depicted by balanced exudation of organic acids.

Physiological and biochemical characterization of Kalongi (Nigella sativa) against arsenic stress: Implications for human health risk assessment

Arsenic (As) is a toxic metalloid that exhibits a varying degree of toxicity in plants depending upon the redox status of its species. Elemental arsenic [As(0)] is the least toxic of all the As species, however, under conducive environmental conditions, it can be readily oxidized into toxic forms. The present experiment was designed to evaluate the deleterious effects of As when applied in As(0) form on the morpho-physiological attributes of Kalongi (Nigella sativa). Seeds of N. sativa were sown in soil contaminated with various levels of As (0, 1.875, 3.75, 7.5, 15.0, and 30.0 mg nA(0) kg^-1 soil). The results indicated that plant biomass and grain yield of N. sativa were not much affected by various levels of As except at 30 mg nA(0) kg^-1 soil. Activities of antioxidant enzymes (SOD, APX, POX, and CAT), phenolic contents, and carotenoids were enhanced in response to the overproduction of H₂O₂, subsequently inhibiting lipid peroxidation. Arsenic accumulation in different plant organs increased with increasing soil As levels in the given trend root > shoot > leaf > seedpod > seed. Arsenic uptake affected the uptake of other elements (P, Fe, Zn, K, Na, Ca). Adaptive changes in total chlorophyll contents, MDA contents, and antioxidant enzymatic defense mechanism in response to As stress suggest that the N. sativa is tolerant to moderate As stress. Therefore, this crop can be cultivated on moderately As-contaminated soils without any significant risks of economic losses and food chain contamination.

Impact of arsenic on phosphate solubilization, acquisition and poly-phosphate accumulation in endophytic fungus Serendipita indica

Symbiotic interactions play a crucial role in the phosphate (Pi) nutrient status of the host plant and offer resilience during biotic and abiotic stresses. Despite a competitive behavior of arsenic (AsV) with Pi, Serendipita indica association promotes plant growth by reducing arsenic bioavailability in the rhizosphere. Reduced arsenic availability is due to the adsorption, accumulation, and precipitation of arsenic in the fungus. The present investigation focused on the fitness and performance of Pi acquisition and utilization in S. indica for growth and metabolism under arsenic stress. The fungus accumulates a massive amount of arsenic up to 2459.3 ppm at a tolerable limit of arsenic supply (1 mM) with a bioaccumulation factor (BAF) 32. Arsenic induces Pi transporter expression to stimulate the arsenic acquisition in the fungus. At the same time, Pi accumulation was also enhanced by 112.2 times higher than the control with an increase in poly-P (polyphosphate) content (6.69 times) of the cell. This result suggests arsenic does not hamper poly-P storage in the cell but shows a marked delocalization of stored poly-P from the vacuoles. Furthermore, an enhanced exopolyphosphatase activity and poly-P storage during arsenic stress suggest induction of cellular machinery for the utilization of Pi is required to deal with arsenic toxicity and competition. However, at high arsenic supply (2.5 and 5 mM), 14.55 and 22.07 times reduced Pi utilization, respectively, was observed during the Pi uptake by the fungus. The reduction of Pi uptake reduces the cell growth and biomass due to competition between arsenic and phosphate. The study suggests no negative impact of arsenic on the Pi acquisition, storage, and metabolism in symbiotic fungus, S. indica, under environmental arsenic contamination.

Selenate increased plant growth and arsenic uptake in As-hyperaccumulator Pteris vittata via glutathione-enhanced arsenic reduction and translocation

The beneficial effects of selenium on As uptake and plant growth in As-hyperaccumulator Pteris vittata are known, but the associated mechanisms remain unclear. Here, we investigated the effects of selenate on arsenic accumulation by P. vittata under two arsenate levels. P. vittata plants were exposed to 13 (As₁₃) or 133 µM (As₁₃₃) arsenate and 5 µM selenate in 0.2-strength Hoagland solution. After 14 d of growth, plant biomass, Se and As content, As speciation, and malondialdehyde (MDA), glutathione reductase (GR), glutathione peroxidase (GPX), and glutathione (GSH and GSSG) levels were determined. The results show that selenate promoted P. vittata growth and increased As concentrations in the roots and fronds by 256% from 97 to 346 mg kg^-1 and 142% from 213 to 514 mg kg^-1 under As₁₃ treatment, and by 166% from 500 to 1332 mg kg^-1 and 534% from 777 to 4928 mg kg^-1 under As₁₃₃ treatment. In addition, selenate increased the glutathione content in P. vittata roots and fronds by 75-86% under As₁₃ treatment and 44-45% under As₁₃₃ treatment. Selenate also increased the GPX activity by 161-173%, and GR activity by 72-79% in P. vittata under As₁₃ and As₁₃₃ treatments. The HPLC-ICP-MS analysis indicated that selenate increased both AsIII and AsV levels in P. vittata, with AsIII/AsV ratio being lower in the roots and higher in the fronds, i.e., more AsIII was being translocated to the fronds. Taken together, our results suggest that, via GPX-GR mediated enhancement of GSH-GSSG cycle, selenate effectively increases plant growth and As uptake in P. vittata by improving AsV reduction in the roots and AsIII translocation from the roots to the fronds.

Molybdenum-induced endogenous nitric oxide (NO) signaling coordinately enhances resilience through chlorophyll metabolism, osmolyte accumulation and antioxidant system in arsenate stressed-wheat (Triticum aestivum L.) seedlings

There is little information available to decipher the interaction between molybdenum (Mo) and nitric oxide (NO) in mitigating arsenic (As^V) stress in plants. The present work highlights the associative role of exogenous Mo and endogenous NO signaling in regulating As^V tolerance in wheat seedlings. Application of Mo (1 μM) on 25-day-old wheat seedlings grown in the presence (5 μM) or absence of As^V stress caused improvement of photosynthetic pigment metabolism, reduction of electrolytic leakage and reactive oxygen species (ROS), and higher accumulation of osmolytes (proline and total soluble sugars). The molybdenum treatment upregulated antioxidative enzymes, such as superoxide dismutase, ascorbate peroxidase and glutathione reductase. In addition, the accumulation of nonenzymatic antioxidants (ascorbate and glutathione) was correlated with an increase in ascorbate peroxidase and glutathione reductase activity. The application of cPTIO (endogenous NO scavenger; 100 μM) reversed the Mo-mediated effects, thus indicating that endogenous NO may accompany Mo-induced mitigation of As^V stress. Mo treatment stimulated the accumulation of endogenous NO in the presence of As^V stress. Thus, it is evident that Mo and NO-mediated As^V stress tolerance in wheat seedlings are primarily operative through chlorophyll restoration, osmolytes accumulation, reduced electrolytic leakage, and ROS homeostasis.

Morphological characteristics and accumulation of arsenic in Argyrochosma formosa (Liebm.) Windham developed in a highly contaminated site with arsenic in Matehuala, SLP, México

We studied the ability of Argyrochosma formosa growing in an arsenic heavily contaminated site to accumulate this metalloid; morphological characteristics and translocation of arsenic were evaluated in the organs. Population census of wild specimens of A. formosa was done, and 14 samples of ferns and rhizosphere soil were collected randomly. We recorded morphological characteristics with scanning electronic microscopy (SEM); concentrations of As in organs of fern plants (root, rhizome, and fronds) were evaluated with inductively coupled plasma-optic emission spectrometry (ICP-OES). Two hundred ninety-four individuals at different stages of development were identified, indicating the establishment of fern on the site. Morphological characteristics of A. formosa in fern plant organs did not show structural effects, compared with herbarium plants. Arsenic distribution in fern plant tissues was 192.2-763.6 mg/kg, 188-1017 mg/kg, and 113-2008 mg/kg, in roots, rhizomes, and fronds, respectively. The calculated bioaccumulation factor in fronds ranged from 2 to 7 and the translocation factor from 0.6 to 2.1. Our data suggest that A. formosa is an arsenic-tolerant species and propose it for phytoremediation on contaminated sites with As concentrations similar to that of the studied location. Further studies should be performed to evaluate the mechanisms of accumulation of As in plant tissues.

Rhizosphere interactions between PAH-degrading bacteria and Pteris vittata L. on arsenic and phenanthrene dynamics and transformation

The pot experiment was conducted to monitor the dynamics in soil solution chemistry in order to determine the main rhizosphere processes determining As and PAH bioavailability when utilizing P. vittata and PAH-degrading bacteria to remediate co-contaminated soils. The result showed that P. vittata was capable of depleting soil solution As and increasing phenanthrene solubilization, and thus facilitating plant As uptake and phenanthrene dissipation. Bacterial inoculation enhanced soil phenanthrene dissipation and concurrently modified As bioavailability though increasing soil pH, facilitating Fe and Ca minerals solubilization, and accelerating organic matter decomposition. However, the main factors that determine As bioavailability in the rhizosphere considerably varied with plant genotypes. Upon bacterial inoculation, P and Fe strongly influenced As(V) availability and its uptake by the Guangxi accession, and DOC, Fe, and pH were the main parameters correlated with As(V) availability in the rhizosphere of the Hunan accession. Bacterial inoculation tended to stimulate As(V) reduction in the rhizosphere of P. vittata. Microbial-induced changes in Ca, S, and C cycling and pH were indicators of As(V) reduction. Although bacterial inoculation increased soil As and phenanthrene availability, striking differences in As and nutrients uptake and phenanthrene dissipation were observed between P. vittata genotypes. It is suggested that apart from the microbial transformation, plant genotypes and bacterial mediated plant nutrition are also the critical factors in controlling the fates of As and phenanthrene. Our results uncovered the interactions between P. vittata and PAH-degrading bacteria on rhizosphere properties and nutrients cycling regulating As and PAH availability and remediation efficiency.

Evaluation of phytoremediation potential of native dominant plants and spatial distribution of heavy metals in abandoned mining area in Southwest China

A field investigation on the content of heavy metals in soils and dominant plants was conducted in three sites (A<0.5 km, B<1.0 km, C<1.5 km) with different distances of mine tailings. The spatial distribution of heavy metals and the accumulation in plants were compared, and the candidate species for ecosystem restoration were selected. The results indicated that the soil was polluted by chromium (Cr), Cadmium (Cd), copper (Cu), nickel (Ni) in varying degrees, which is 2.07, 2.60, 1.79, and 4.49 times higher than the Class-Ⅱ standard in China. The concentrate of Ni, Cd, and Zinc (Zn) increased, while Cr, Lead (Pb), and Cu decreased with the distance from the mine tailings. 73 species (34 families) were found and mainly herbaceous plants. The concentrate of Cd, Cu, Cr, and Ni in 29 dominant plants were measured and 66.67%, 21.43%, 100%, 47.62% plants exceeded the normal concentration range. Based on the comparative analysis of heavy metal content, bioconcentration factor, and translocation factor in plants, Polygonum capitatum has good phytoextraction ability, Boehmeria nivea, Chrysanthemum indicum, Miscanthus floridulus, Conyza canadensis, Rubus setchuenensis, Senecio scandens, and Arthraxon hispidus showed remarkable phytostabilization abilities of Cr, Cd, Ni, and Cu, which can be used as potential phytoremediation candidate.

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.

A Test of the Inadvertent Uptake Hypothesis Using Plant Species Adapted to Serpentine Soil

Serpentine soils are a stressful growing environment for plants, largely due to nutrient deficiencies and high concentrations of toxic heavy metals (e.g., Ni). Plants have evolved various adaptations for tolerating these extreme environments, including metal hyperaccumulation into above-ground tissues. However, the adaptive significance of metal hyperaccumulation is a topic of debate, with several non-mutually-exclusive hypotheses under study. For example, the inadvertent uptake hypothesis (IUH) states that heavy metal accumulation is a consequence of an efficient nutrient-scavenging mechanism for plants growing in nutrient-deficient soils. Thus, it is possible that metal hyperaccumulation is simply a byproduct of non-specific ion transport mechanisms allowing plants to grow in nutrient-deficient soils, such as serpentine soils, while simultaneously tolerating other potentially toxic heavy metals. Furthermore, some nutrient needs are tissue-specific, and heavy metal toxicity can be more pronounced in reproductive tissues; thus, studies are needed that document nutrient and metal uptake into vegetative and reproductive plant tissues across species of plants that vary in the degree to which they accumulate soil metals. To test these ideas, we grew nine plant species that are variously adapted to serpentine soils (i.e., Ni-hyperaccumulating endemic, non-hyperaccumulating endemic, indicator, or indifferent) in a common garden greenhouse experiment. All species were grown in control soils, as well as those that were amended with the heavy metal Ni, and then analyzed for macronutrient (Ca, Mg, K, and P), micronutrient (Cu, Fe, Zn, Mn, and Mo), and heavy metal (Cr and Co) concentrations in their vegetative and reproductive organs (leaves, anthers, and pistils). In accordance with the IUH, we found that hyperaccumulators often accumulated higher concentrations of nutrients and metals compared to non-hyperaccumulating species, although these differences were often organ-specific. Specifically, while hyperaccumulators accumulated significantly more K and Co across all organs, Cu was higher in leaves only, while Mn and Zn were higher in anthers only. Furthermore, hyperaccumulators accumulated significantly more Co and Mo across all organs when Ni was added to the soil environment. Our work provides additional evidence in support of the IUH, and contributes to our understanding of serpentine adaptation in plants.

Mitigation of arsenate toxicity by indole-3-acetic acid in brinjal roots: Plausible association with endogenous hydrogen peroxide

The role of indole-3-acetic acid (IAA) and hydrogen peroxide (H₂O₂) crosstalk in regulating metal stress is still less known. Herein, role of IAA in alleviating arsenate (As^V) toxicity in brinjal seedlings along with its probable relation with endogenous H₂O₂ was investigated. Arsenate hampered root growth due to greater accumulation of As and decrease in phosphorus uptake that resulted into inhibited photosynthesis and cell death. Further, As^V induced oxidative stress markers and damage to macromolecules (lipids and proteins) due to alterations in redox status of glutathione as a result of inhibition in activity of glutathione synthetase and glutathione reductase. However, application of IAA with As^V improved root growth by significantly declining As accumulation and oxidative stress markers, sequestrating As into vacuoles, and improving redox status of glutathione which collectively protected roots from cell death. Interestingly, addition of diphenylene iodonium (DPI, an inhibitor of NADPH oxidase) further increased As^V toxicity even in the presence of IAA. However, application of H₂O₂ rescued negative effect of DPI. Overall, the results suggested that in IAA-mediated mitigation of As^V toxicity in brinjal roots, endogenous H₂O₂ might have acted as a downstream signal.

Hyperaccumulation and transport mechanism of thallium and arsenic in brake ferns (Pteris vittata L.): A case study from mining area

Both thallium (Tl) and arsenic (As) bear severe toxicity. Brake fern (Pteris vittata L.) is well-known for its hyperaccumulation capacity of As, yet its role on Tl accumulation remains unknown. Herein, brake ferns growing near an As tailing site in Yunnan, Southwestern China are for the first time discovered as a co-hyperaccumulator of both Tl and As. The results showed that the brake ferns extracted both As and Tl efficiently from the soils into the fronds. The studied ferns growing on Tl and As co-polluted soils were found to accumulate extremely high levels of both As (7215-11110 mg/kg) and Tl (6.47-111 mg/kg). Conspicuously high bio-accumulation factor (BCF) was observed for As (7.8) and even higher for Tl (28.4) among these co-hyperaccumulators, wherein the contents of As and Tl in contaminated soils were 1240 ± 12 and 3.91 ± 0.01 mg/kg, respectively. The applied advanced characterization techniques (e.g. transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS)) indicated a preferential uptake of Tl(I) while simultaneous accumulation of As (III) and As(V) from the Tl(I)/Tl(III)-As (III)/As(V) co-existent rhizospheric soils. The findings benefit the phytoremediation practice and pose implications for managing and restoring Tl-As co-contaminated soils in other countries.

Exogenous melatonin-mediated modulation of arsenic tolerance with improved accretion of secondary metabolite production, activating antioxidant capacity and improved chloroplast ultrastructure in rosemary herb

Arsenic (As) recognized as a group I human carcinogen additionally poses a threat to plants which limit growth, metabolic activity, and productivity. Melatonin (MEL) is a naturally occurring compound in plants that have been recognized to mediate numerous morphological, physiological and molecular processes. Conversely, the role of MEL in inducing As-tolerance remains inexpressible and the plausible mechanisms in inducing As tolerance have remained largely unknown. The present investigation was designed to understand the protective role of MEL concentrations in rosemary herbs cultivated under As contamination. Arsenic evoked a deleterious decline on herb productivity, photosynthetic pigment, ion concentration, water status, ascorbic acid, essential oil (EO) yield and induced malformation of the chloroplast. Alternatively, increased organic osmolytes, oxidative impairment criteria, additionally antioxidant enzymes, phenol, flavonoid, anthocyanin, and EO%. Exogenous application of MEL with or without As, considerably increased growth, photosynthetic pigment, ion concentration, organic osmolytes as well as EO yield regarding polluted or non-polluted treatment respectively. Moreover, MEL treatment stabilized the cell membrane integrity, suppressed oxidative impairment criteria, and enhanced antioxidant capacity, additionally upregulation antioxidant enzymes. Plant treated with As showed a significant increase in As contamination and a bioconcentration factor in both root and shoot system. MEL supplementation under normal or As concentration, reduced As accumulation and bioconcentration factors, in either shoot or root systems. Additionally As decrease transfer factor, however, supplementation of MEL further decreased it. Application of 50 μM MEL might help the herbs to withstand As stress by strengthening their antioxidant machinery and osmoregulation capacity.

Interactive effects of As, Cd and Zn on their uptake and oxidative stress in As-hyperaccumulator Pteris vittata

The effects of arsenic (As), cadmium (Cd) and zinc (Zn) on each other's uptake and oxidative stress in As-hyperaccumulator Pteris vittata were investigated. P. vittata plants were exposed to 50 μM As, Cd and/or Zn for 15 d in 0.2-strength Hoagland solution. When applied alone, P. vittata accumulated 185 mg kg^-1 As, 164 mg kg^-1 Cd and 327 mg kg^-1 Zn in the fronds. While Cd and Zn did not impact each other's uptake, As affected Cd and Zn uptake. Whereas As decreased Zn uptake, Zn affected As speciation in P. vittata fronds, with more arsenate (AsV) than arsenite (AsIII) being present. At 50 μM As, 75 μM Zn increased As accumulation in P. vittata fronds by 10 folds to 2363 mg kg^-1 compared to 50 μM Zn. Although AsV was the predominant As species in all tissues, Cd enhanced AsIII levels in the fronds but increased AsV in the roots. Co-exposure of Cd + Zn elevated oxidative stress basing on thiobarbituric acid reactive substances, H₂O₂ content, Evans blue dye uptake, membrane injury index and reactive oxygen species (ROS) relative to single metal. By lowering Cd and Zn concentrations in P. vittata fronds, As reduced the associated stress comparative to Cd or Zn treatment. The results enhance our understanding of the mechanisms underlying the interactions between As, Cd and Zn in As-hyperaccumulator P. vittata.