Chromate and phosphate inhibited each other's uptake and translocation in arsenic hyperaccumulator Pteris vittata L

Hexavalent chromium uptake in rice (Oryza sativa L.) mediated by sulfate and phosphate transporters OsSultr1;2 and OsPht1;1

Chromium (Cr) soil contamination is a critical global environmental concern, with hexavalent chromium (Cr[VI]) being especially perilous due to its high mobility, bioavailability, and phytotoxicity. This poses a significant threat to the cultivation of crops, particularly rice, where the mechanisms of Cr(VI) absorption remain largely unexplored. This study uncovered a competitive interaction between Cr(VI) and essential nutrients-sulfate and phosphate during the uptake process. Notably, deficiencies in sulfate and phosphate were associated with a marked increase in Cr(VI) accumulation in rice, reaching up to 76.5 % and 77.7 %, respectively. Employing q-PCR, this study identified significant up-regulation of the sulfate transporter gene, OsSultr1;2, and the phosphate transporter gene, OsPht1;1, in response to Cr(VI) stress. Genetic knockout studies have confirmed the crucial role of OsSultr1;2 in Cr(VI) uptake, with its deletion leading to a 36.1 % to 69.6 % decrease in Cr uptake by rice roots. Similarly, the knockout of OsPht1;1 resulted in an 18.1 % to 25.7 % decrease in root Cr accumulation. These findings highlight the key role of the sulfate transporter OsSultr1;2 in Cr(VI) uptake, with phosphate transporters also contributing significantly to the process. These insights are valuable for developing rice varieties with reduced Cr(VI) accumulation, ensuring the safety of rice grain production.

Selenium alleviates chromium stress and promotes chromium uptake in As-hyperaccumulator Pteris vittata: Cr reduction and cellar distribution

Arsenic-hyperaccumulator Pteris vittata exhibits remarkable absorption ability for chromium (Cr) while beneficial element selenium (Se) helps to reduce Cr-induced stress in plants. However, the effects of Se on the Cr uptake and the associated mechanisms in P. vittata are unclear, which were investigated in this study. P. vittata plants were grown for 14 days in 0.2-strength Hoagland solution containing 10 (Cr10) or 100 μM (Cr100) chromate (CrVI) and 1 μM selenate (Se1). The plant biomass, malondialdehyde contents, total Cr and Se contents, Cr speciation, expression of genes associated with Cr uptake, and Cr subcellular distribution in P. vittata were determined. P. vittata effectively accumulated Cr by concentrating 96-99% in the roots under Cr100 treatment. Further, Se substantially increased its Cr contents by 98% to 11,596 mg kg-1 in the roots, which may result from Se's role in reducing its oxidative stress as supported by 27-62% reduction in the malondialdehyde contents. Though supplied with CrVI, up to 98% of the Cr in the roots was reduced to insoluble chromite (CrIII), with 83-89% being distributed on root cell walls. Neither Cr nor Se upregulated the expression of sulfate transporters PvSultr1;1-1;2 or phosphate transporter PvPht1;4, indicating their limited role in Cr uptake. P. vittata effectively accumulates Cr in the roots mainly as CrIII on cell walls and Se effectively enhances its Cr uptake by reducing its oxidative stress. Our study suggests that Se can be used to enhance P. vittata Cr uptake and reduce its oxidative stress, which may have application in phytostabilization of Cr-contaminated soils.

Quantifying and normalizing the combined phytotoxicity of mixed-valence chromium in soil integrated by toxicity equivalence

When Cr(VI) and Cr(III) coexist, the reasonable assessment of the combined toxicity of chromium in soil and its ecological risk is still not well resolved. In the present study, exogenous mixed concentration combinations were set up to determine the interaction and combined toxicity of Cr(VI) and Cr(III), which were quantified as measured total and resin extractable forms for dose-response experiments with barley root elongation. The concept of toxicity equivalence "α" (the ratio of toxicity intensity coefficient between Cr(VI) and Cr(III), which can be expressed as the relative toxic strength of Cr(VI) to Cr(III)) was proposed for the toxicity assessment of mixed-valence chromium in soil. The results showed that the dose-response relationship was determined more precisely by the extended independent action model (e-IA) than traditional models (e.g., concentration addition model), and the mutual antagonism for resin extractable form (Resin-Cr) was stronger than the measured total form (T-Cr). The values of toxicity equivalence (α) between coexisting Cr(VI) and Cr(III) as Resin-Cr and T-Cr were 0.74 and 160, respectively, which indicated Resin-Cr(III) had relatively stronger toxicity than Resin-Cr(VI), while T-Cr(III) was much less than T-Cr(VI). The α values between Cr(VI) and Cr(III) decreased with their more active forms (decreased to about 0.5% of the original), even as total concentration and activity in solutions, making a dialectical view of the toxicity of both in different forms necessary. Finally, the log-logistic models were developed, enabling mixed-valence Cr toxicity to be assessed from a unilateral perspective using the Cr(III) equivalence concentration (Cr(III)-eq). This work provided innovative ideas for ecological threshold studies for mixed-valence metals in soils.

Assessment of bioremediation potential of Calotropis procera and Nerium oleander for sustainable management of vehicular released metals in roadside soils

Land transportation is a major source of heavy metal contamination along the roadside, posing significant risks to human health through inhalation, oral ingestion, and dermal contact. Therefore, this study has been designed to determine the concentrations of vehicular released heavy metals (Cd, Pb, Ni, and Cu) in roadside soil and leaves of two commonly growing native plant species (Calotropis procera and Nerium oleander).Two busy roads i.e., Lahore-Okara road (N-5) and Okara-Faisalabad roads (OFR) in Punjab, Pakistan, were selected for the study. The data were collected from five sites along each road during four seasons. Control samples were collected ~ 50 m away from road. The metal content i.e. lead (Pb), cadmium (Cd) nickel (Ni) and copper (Cu) were determined in the plant leaves and soil by using Atomic Absorption Spectrophotometer (AAS). Significantly high amount of all studied heavy metals were observed in soil and plant leaves along both roads in contrast to control ones. The mean concentration of metals in soil ranged as Cd (2.20-6.83 mg/kg), Pb (4.53-15.29 mg/kg), Ni (29.78-101.26 mg/kg), and Cu (61.68-138.46 mg/kg) and in plant leaves Cd (0.093-0.53 mg/kg), Pb (4.31-16.34 mg/kg), Ni (4.13-16.34 mg/kg) and Cu (2.98-32.74 mg/kg). Among roads, higher metal contamination was noted along N-5 road. Significant temporal variations were also noted in metal contamination along both roads. The order of metal contamination in soil and plant leaves in different seasons was summer > autumn > spring > winter. Furthermore, the metal accumulation potential of Calotropis procera was higher than that of Nerium oleander. Therefore, for sustainable management of metal contamination, the plantation of Calotropis procera is recommended along roadsides.

Biomass production and uptake of sulfur, chromium and micronutrients by Tanzania guinea grass grown with sulfur and chromium

Soil contamination caused by improper waste disposal can affect plant growth. Tropical forage plants have rapid growth, high biomass production and vigorous regrowth. Chromium (Cr) is one of the most common contaminants in the environment. Sulfur (S) is a nutrient involved in various cell detoxification processes. The objective was to assess the effects of excess Cr on biomass production and concentrations of this metal, S and cationic micronutrients, under conditions of varying supply of S for Tanzania guinea grass. The experiment was conducted in randomized complete blocks in a 3 × 4 factorial scheme, corresponding to three levels of S (0.1, 1.9 and 3.7 mmol L^-1) and four levels of Cr (0.0, 0.5, 1.0 and 2.0 mmol L^-1) in three replicates. Root surface area, shoot and root biomass production, concentrations of total S, sulfate-S, Cr and cationic micronutrients, and Cr transport factor were determined. S level of 1.9 mmol L^-1 reduced the toxicity by Cr in Tanzania guinea grass, expressed by the higher shoot and root dry weight production, greater stability in the cellular concentration of sulfate-S and higher concentrations of micronutrients. It was concluded that the high availability of S reduced the toxicity by Cr(VI) in Tanzania guinea grass, expressed by the higher shoot and root dry weight production, greater stability in the cellular concentration of sulfate-S and higher concentration of micronutrients in the grass shoots.

Chromium Contamination and Health Risk Assessment of Soil and Agricultural Products in a Rural Area in Southern China

With the rapid development of industry, chromium (Cr) pollutants accumulate constantly in the soil, causing severe soil Cr pollution problems. Farmland Cr pollution hurts the safety of agricultural production and indirectly affects human health and safety. However, the current situation of Cr pollution in farmland soil and crops has not been detailed enough. In this study, the evaluation of Cr potential risk in soil-crop systems was conducted in a rural area that was affected by industry and historic sewage irrigation. Ten different crops and rhizosphere soils were sampled from four fields. The results showed that Cr contents in farmland soil exceeded the national standard threshold in China (>21.85%), and the Cr content in edible parts of some agricultural products exceeded that too. According to the PCA and relation analysis, the Cr accumulation in edible parts showed a significant correlation with soil Cr contents and available potassium contents. Except for water spinach, the target hazard quotient (THQ) of the other crops was lower than 1.0 but the carcinogenic health risks all exceeded the limits. The carcinogenic risks (CR) of different types of crops are food crops > legume crops > leafy vegetable crops and root-tuber crops. A comprehensive assessment revealed that planting water spinach in this area had the highest potential risk of Cr pollution. This study provided a scientific and reliable approach by integrating soil environmental quality and agricultural product security, which helps evaluate the potential risk of Cr in arable land more efficiently and lays technical guidelines for local agricultural production safety.

Chromium in plant-soil nexus: Speciation, uptake, transport and sustainable remediation techniques

Heavy metal (HM) pollution has become a serious global problem due to the non-biodegradable nature of the HMs and their persistence in the environment. Agricultural soil is a non-renewable resource that requires careful management so that it can fulfill the increasing demand for agricultural food production. However, different anthropogenic activities have resulted in a large-scale accumulation of HMs in soil which is detrimental to soil and plant health. Due to their ubiquity, increased bioavailability, toxicity, and non-biodegradable nature, HM contamination has formed a roadblock in the way of achieving food security, safety, and sustainability in the future. Chromium (Cr), specifically Cr(VI) is a highly bioavailable HM with no proven role in the physiology of plants. Chromium has been found to be highly toxic to plants, with its toxicity also influenced by chemical speciation, which is in turn controlled by different factors, such as soil pH, redox potential, organic matter, and microbial population. In this review, the different factors that influence Cr speciation were analyzed and the relationship between biogeochemical transformations of Cr and its bioavailability which may be beneficial for devising different Cr remediation strategies has been discussed. Also, the uptake and transport mechanism of Cr in plants, with particular reference to sulfate and phosphate transporters has been presented. The biological solutions for the remediation of Cr contaminated sites which offer safe and viable alternatives to old-style physical and chemical remediation strategies have been discussed in detail. This review provides theoretical guidance in developing suitable approaches for the better management of these remediation strategies.

Selenium Increased Arsenic Accumulation by Upregulating the Expression of Genes Responsible for Arsenic Reduction, Translocation, and Sequestration in Arsenic Hyperaccumulator Pteris vittata

Selenate enhances arsenic (As) accumulation in As-hyperaccumulator Pteris vittata, but the associated molecular mechanisms are unclear. Here, we investigated the mechanisms of selenate-induced arsenic accumulation by exposing P. vittata to 50 μM arsenate (AsV₅₀) and 1.25 (Se_1.25) or 5 μM (Se₅) selenate in hydroponics. After 2 weeks, plant biomass, plant As and Se contents, As speciation in plant and growth media, and important genes related to As detoxification in P. vittata were determined. These genes included P transporters PvPht1;3 and PvPht1;4 (AsV uptake), arsenate reductases PvHAC1 and PvHAC2 (AsV reduction), and arsenite (AsIII) antiporters PvACR3 and PvACR3;2 (AsIII translocation) in the roots, and AsIII antiporters PvACR3;1 and PvACR3;3 (AsIII sequestration) in the fronds. The results show that Se_1.25 was more effective than Se₅ in increasing As accumulation in both P. vittata roots and fronds, which increased by 27 and 153% to 353 and 506 mg kg^-1. The As speciation analyses show that selenate increased the AsIII levels in P. vittata, with 124-282% more AsIII being translocated into the fronds. The qPCR analyses indicate that Se_1.25 upregulated the gene expression of PvHAC1 by 1.2-fold, and PvACR3 and PvACR3;2 by 1.0- to 2.5-fold in the roots, and PvACR3;1 and PvACR3;3 by 0.6- to 1.1-fold in the fronds under AsV₅₀ treatment. Though arsenate enhanced gene expression of P transporters PvPht1;3 and PvPht1;4, selenate had little effect. Our results indicate that selenate effectively increased As accumulation in P. vittata, mostly by increasing reduction of AsV to AsIII in the roots, AsIII translocation from the roots to fronds, and AsIII sequestration into the vacuoles in the fronds. The results suggest that selenate may be used to enhance phytoremediation of As-contaminated soils using P. vittata.

Mathematical quantification of interactive complexity of transcription factors involved in proline-mediated regulative strategies in Oryza sativa under chromium stress

Involvement of transcription factor (TFs) in governing genes at transcription or post transcription level is known to have affirmative impact on plant physiological and morphological development, especially during environmental abuse. Application of exogenous proline (Pro) is one among the effective approaches to strengthen plant resistance against stresses. However, Pro-mediated regulative strategies of TFs in responses to the chromium (Cr) in rice plants through the gene interaction network are still not clear. In the current study, Pro-mediated interactive complexity of various TFs (i.e., MYB, NAC, WRKY, bHLH, and bZIP) under hexavalent chromium [Cr(VI)] was investigated using Agilent 4 × 44 K rice gene chip and gene interactive probability model (GIPM). Results showed that exogenous Pro had a negligible effect on Cr uptake in rice plants, while a small positive response in biomass accretion of rice seedlings was observed under Cr(VI)+Pro treatments which was to certain extend greater than single Cr(VI) treatments. Rice microarray analysis showed that Cr(VI) significantly (p < 0.05) repressed the expression of TFs in the rice roots and shoots, while the application of exogenous Pro significantly (p < 0.05) up-regulated the expression levels of some TFs in rice tissues. Mathematical modularization indicated that Pro-mediated interaction between MYB and NAC carried more weightage than other TFs in rice roots and shoots under Cr(VI) stress. Overall, our study provides convincing evidence to confirm a positive role of exogenous Pro on reducing the negative impact exerted by Cr(VI) on rice plants through regulating expression and interaction of different TFs.

Effects of copper and arsenic on their uptake and distribution in As-hyperaccumulator Pteris vittata

Arsenic (As) and copper (Cu) are common co-contaminates in soils. However, their interactive effects on their accumulation and distribution in As-hyperaccumulator Pteris vittata are poorly understood. A hydroponic experiment was conducted with As being 0, 5, or 50 μM and Cu being 0.32, 3.2, or 32 μM to evaluate their phytotoxicity, accumulation, and distribution in P. vittata. In addition, As and Cu uptake kinetics were examined using the Michaelis-Menten kinetics model. Total As and Cu concentrations in P. vittata were up to 487 and 1355 mg kg^-1. About 39-81% of the As was in the fronds compared to 0.6-18% for Cu. At 50 μM As, increasing Cu concentration from 0.32 to 32 μM increased root As while decreasing frond As concentrations, with the translocation factor (ratio of As in fronds to roots) being reduced from 4.0 to 0.31. In contrast, As did not affect Cu accumulation in P. vittata. Michaelis constant K_m value for As was higher than that of Cu (6.49-24.9 vs. 0.43-3.36), consistent with higher Cu uptake than As. Besides, Cu reduced root K but increased P levels in the roots, whereas As increased the K and P concentrations in the fronds. Our results suggest that P. vittata accumulated more Cu than As in the roots, contributing to its low As translocation. As such, high levels of Cu are likely to reduce As uptake by P. vittata during phytoremediation of As-contaminated sites.

Chromium biogeochemical behaviour in soil-plant systems and remediation strategies: A critical review

Chromium (Cr) is a toxic heavy metal that is heavily discharged into the soil environment due to its widespread use and mining. High Cr levels may pose toxic hazards to plants, animals and humans, and thus have attracted global attention. Recently, much progress has been made in elucidating the mechanisms of Cr uptake, transport and accumulation in soil-plant systems, aiming to reduce the toxicity and ecological risk of Cr in soil; however, these topics have not been critically reviewed and summarised to date. Accordingly, based on available data-especially from the last five years (2017-2021)-this review traces a plausible link among Cr sources, levels, chemical forms, and phytoavailability in soil; Cr accumulation and translocation in plants; and Cr phytotoxicity and detoxification in plants. Additionally, given the toxicity and hazard posed by Cr(VI) in soils and the application of reductant materials to reduce Cr(VI) to Cr(III) for the remediation of Cr(VI)-contaminated soils, the reduction and immobilisation mechanisms by organic and inorganic reductants are summarised. Finally, some priority research challenges concerning the biogeochemical behaviour of Cr in soil-plant systems are highlighted, as well as the environmental impacts resulting from the application of reductive materials and potential research prospects.

Biochar impact on chromium accumulation by rice through Fe microbial-induced redox transformation

Iron (Fe) dissimilatory reduction might impact chromium (Cr) mobility in the rice rhizosphere, but it is poorly understood. We assessed rhizosphere microbes' role in Cr immobilization and bioavailability by conducting the pot experiment to test different biochar sources (PMB - pig manure and PSB - pine sawdust) and phosphorus (P) levels impact on Cr mobility. Results showed that PMB application increased root biomass (23-65 %) and decreased root Cr concentration (46-74 %) regardless P treatment. However, P addition reduced root and shoot biomass in control and PMB treatments by 33-43 % and 25-26 %. Therefore, low P input is recommended in Cr-contaminated soil. Moreover, Geobacter was the key microbial groups which may be involved in promoting Cr release by increasing Fe dissolution. Finally, Geobacter and Fe dissimilatory reduction play a central role in Cr translocation and they should be considered in strategies to reduce rice Cr uptake by biochar application.

Phosphorus Enhances Cr(VI) Uptake and Accumulation in Leersia hexandra Swartz

The effects of P supplementation on chromium(VI) uptake by Leersia hexandra Swartz were studied using pot-culture experiment. P-deficiency and zero-P addition controls were included. The Cr(VI) uptake followed Michaelis-Menten kinetics. Compare with the control, the P-supply decreased the Michaelis constant (Km) by 16.9% and the P-deficiency decreased the maximum uptake velocity (V_max) by 18%, which indicated no inhibition and competition between P and Cr(VI) uptake by L. hexandra. Moreover, there were a synergistic action between P and Cr(VI) suggests that Cr(VI) uptake by the roots of L. hexandra may be an active process. The bioconcentration factor (BCF) and the transport factor (TF') increased with the increase in P supply. The highest BCF was 3.6-folds higher than the control, indicating that the additional P contribute to a higher ability of L. hexandra transporting Cr from root to the aboveground parts.

Phytate promoted arsenic uptake and growth in arsenic-hyperaccumulator Pteris vittata by upregulating phosphorus transporters

While phosphate (P) inhibits arsenic (As) uptake by plants, phytate increases As uptake by As-hyperaccumulator Pteris vittata. Here we tried to understand the underling mechanisms by investigating the roles of phytate in soil As desorption, P transport in P. vittata, short-term As uptake, and plant growth and As accumulation from soils. Sterile soil was used to exclude microbial degradation on phytate. Results showed that inorganic P released 3.3-fold more As than that of phytate from soil. However, P. vittata accumulated 2-2.5 fold more As from soils with phytate than that in control and P treatment. In addition, different from P suppression on As uptake, solution uptake experiment showed that As uptake in phytate treatment was comparable to that of control under 0.1-7.5 μM As after 1-24 h. Moreover, responding to phytate, P. vittata P transporter PvPht1;3 increased by 3-fold while PvPht1;1 decreased by 65%. The data suggested that phytate upregulated PvPht1;3, thereby contributing to As uptake in P. vittata. Our results showed that, though with lower As release from soil compared to P, phytate induced more As uptake and better growth in P. vittata by upregulating P transporters.

Speciation, bioaccessibility and potential risk of chromium in Amazon forest soils

Even though the Amazon region is widely studied, there is still a gap regarding Cr exposure and its risk to human health. The objectives of this study were to 1) determine Cr concentrations in seven chemical fractions and 6 particle sizes in Amazon soils, 2) quantify hexavalent Cr (CrVI) concentrations using an alkaline extraction, 3) determine the oral and lung bioaccessible Cr, and 4) assess Cr exposure risks based on total and bioaccessible Cr in soils. The total Cr in both A (0-20 cm) and B (80-100 cm) horizons was high at 2346 and 1864 mg kg^-1. However, sequential extraction indicated that available Cr fraction was low compared to total Cr, with Cr in the residual fraction being the highest (74-76%). There was little difference in total Cr concentrations among particle sizes. Hexavalent Cr concentration was also low, averaging 0.72 and 2.05 mg kg^-1 in A and B horizon. In addition, both gastrointestinal (21-22 mg kg^-1) and lung (0.95-1.25 mg kg^-1) bioaccessible Cr were low (<1.2%). The low bioavailability of soil Cr and its uniform distribution in different particle sizes indicated that Cr was probably of geogenic origin. Exposure based on total Cr resulted in daily intake > the oral reference dose for children, but not when using CrVI or bioaccessible Cr. The data indicated that it is important to consider both Cr speciation and bioaccessibility when evaluating risk from Cr in Amazon soils.

Ecotoxicological and Interactive Effects of Copper and Chromium on Physiochemical, Ultrastructural, and Molecular Profiling in Brassica napus L

Heavy metal accumulation causes huge environmental problems, particularly in agricultural ecosystems which have deteriorative effects on the yield and quality of crops. Individual copper (Cu) and chromium (Cr) effects have been investigated extensively in plants; however, co-contamination of Cu and Cr induced stress on Brassica napus L. is still unclear. In the present experiment, the interactive effects of Cu and Cr were studied in two B. napus cultivars (Zheda 622 and ZS 758). Results showed that the application of Cr was more toxic than Cu, and their combined stress had shown a significant adverse effect on plant growth. Biomass and photosynthetic pigment were decreased remarkably under all metal treatments. Individual treatments of Cu and Cr and their combination cause the accumulation of ROS and lipid peroxidation. Moreover, the activities of antioxidant enzymes and their mRNA transcription levels, such as catalase (CAT), ascorbate peroxidase, glutathione reductase, superoxide dismutase, and peroxidase, were increased, especially when treated with Cr alone or under Cu+Cr combined treatment in both cultivars, except for the CAT activity which was decreased in both leaves and roots of sensitive cultivar Zheda 622 as compared with their respective controls. Additionally, nonenzymatic antioxidants like reduced and oxidized glutathione showed a differential activity pattern in roots and leaves of both cultivars. A more pronounced modification in chloroplast ultrastructure was observed in both cultivars under Cu+Cr treatment followed by Cr and Cu alone treatments. Furthermore, synergistic effects of Cu and Cr were prominent; this may be due to the enhanced metals uptake under combined treatment, which suggests that Cr and Cu interaction is not competitive but is rather additive and genotypic-dependent.

Assisted green remediation of chromium pollution

The effects of application of two anions commonly found in subsurface environments, phosphate (PO₄^3-) and sulfate (SO₄^2-), on hexavalent chromium (Cr(VI)) uptake and translocation by Zea mays, were investigated using pot-culture experiments. The two anions were tested as potential agents to mobilize Cr(VI) from polluted soil (50, 75 and 100 mg kg^-1 dw) at a dose of 16.7 mmol kg^-1. Metal uptake from soil to roots and subsequent transfer to shoots was discussed in terms of bioconcentration factor (BCF) and translocation factor (TF). The overall order of BCFs and TFs which resulted from this study was: PO₄^3- > H₂O > SO₄^2-; in the same time, metal concentration in plants tissues decreased in the order: root > stem > leaf. The present study suggests that PO₄^3- may be used as an environmentally compatible alternative to non-biodegradable synthetic chelants, to enhance the efficiency of Cr(VI) phytoextraction with Z. mays.

Kinetics, biochemical and factorial analysis of chromium uptake in a multi-ion system by Tradescantia pallida (Rose) D. R. Hunt

Discharge of wastewater from electroplating and leather industries is a major concern for the environment due to the presence of toxic Cr⁶⁺ and other ions, such as sulfate, nitrate, phosphate, etc. This study evaluated the potential of Tradescantia pallida, a plant species known for its Cr bioaccumulation, for the simultaneous removal of Cr⁶⁺, SO₄^2-, NO₃^-, and PO₄^3-. The effect of different co-ions on Cr⁶⁺ removal by T. pallida was examined following the Plackett-Burman design of experiments carried out under batch hydroponics conditions. The results revealed a maximum removal of 84% Cr⁶⁺, 87% SO₄^2-, 94% NO₃^- and 100% PO₄^3- without any phytotoxic effect on the plant for an initial Cr⁶⁺ concentration in the range 5-20 mg L^-1. SO₄^2- and NO₃^- enhanced Cr uptake at a high initial Cr concentration (20 mg L^-1), whereas PO₄^3- did not affect Cr uptake both at high and low initial Cr concentrations. The Cr⁶⁺ removal kinetics in the presence of different ions was well described by the pseudo-second-order kinetic model which revealed that both biosorption and bioaccumulation of the metal played an important role in Cr⁶⁺ removal. Increase in the total carbohydrate and protein content of the plant following Cr⁶⁺ and co-ions exposure indicated a good tolerance of the plant toward Cr⁶⁺ toxicity. Furthermore, enhancement in the lipid peroxidation and catalase activity in T. pallida upon Cr⁶⁺ exposure revealed a maximum stress-induced condition in the plant. Overall, this study demonstrated a very good potential of the plant T. pallida for Cr⁶⁺ removal from wastewater even in the presence of co-ions.

Phytate induced arsenic uptake and plant growth in arsenic-hyperaccumulator Pteris vittata

Phytate is abundant in soils, which is stable and unavailable for plant uptake. However, it occurs in root exudates of As-hyperaccumulator Pteris vittata (PV). To elucidate its effect on As uptake and growth, P. vittata were grown on agar media (63 μM P) containing 50 μM As and/or 50 or 500 μM phytate with non As-hyperaccumulator Pteris ensiformis (PE) as a congeneric control for 60 d. Phytate induced efficient As and P uptake, and enhanced growth in PV, but had little effects on PE. The As concentrations in PV fronds and roots were 157 and 31 mg kg^-1 in As₅₀+phytate₅₀, 2.2- and 3.1-fold that of As₅₀ treatment. Phosphorus uptake by PV was reduced by 27% in As treatment than the control (P vs. P+As) but increased by 73% comparing phytate₅₀₀ to phytate₅₀₀+As, indicating that PV effectively took up P from phytate. Neither As nor phytate affected Fe accumulation in PV, but phytate reduced root Fe concentration in PE (46-56%). As such, the increased As and P and the unsuppressed Fe uptake in PV probably promoted PV growth. Thus, supplying phytate to As-contaminated soils may promote As uptake and growth in PV and its phytoremediation ability.

Arsenic-induced plant growth of arsenic-hyperaccumulator Pteris vittata: Impact of arsenic and phosphate rock

Phosphate rock (PR) has been shown to promote plant growth and arsenic (As) uptake by As-hyperaccumulator Pteris vittata (PV). However, little is known about its behaviors in agricultural soils. In this study, impact of 50 mg kg(-1) As and/or 1.5% PR amendment on plant As accumulation and growth was investigated by growing PV for 90 d in three agricultural soils. While As amendment significantly increased plant As uptake and substantially promoted PV growth, the opposite was observed with PR amendment. Arsenic amendment increased plant frond As from 16.9-265 to 961-6017 mg kg(-1),whereas PR amendment lowered frond As to 10.2-216 mg kg(-1). The As-induced plant growth stimulation was 69-71%. While PR amendment increased plant Ca and P uptake, As amendment showed opposite results. The PV biomass was highly correlated with plant As at r = 0.82, but with weak correlations with plant Ca or P at r < 0.30. This study confirmed that 1) As significantly promoted PV growth, probably independent of Ca or P uptake, 2) PR amendment didn't enhance plant growth or As uptake by PV in agricultural soils with adequate available P, and 3) PV effluxed arsenite (AsIII) growing in agricultural soils.

Sulfate and chromate increased each other's uptake and translocation in As-hyperaccumulator Pteris vittata

We investigated the effects of chromate (CrVI) and sulfate on their uptake and translocation in As-hyperaccumulator Pteris vittata. Plants were exposed to 1) 0.1 mM CrVI and 0, 0.25, 1.25 or 2.5 mM sulfate or 2) 0.25 mM sulfate and 0, 0.5, 2.5 or 5.0 mM CrVI for 1 d in hydroponics. P. vittata accumulated 26 and 1261 mg kg(-1) Cr in the fronds and roots at CrVI0.1, and 2197 and 1589 mg kg(-1) S in the fronds and roots at S0.25. Increasing sulfate concentrations increased Cr root concentrations by 16-66% and helped CrVI reduction to CrIII whereas increasing CrVI concentrations increased frond sulfate concentrations by 3-27%. Increasing sulfate concentrations enhanced TBARS concentrations in the biomass, indicating oxidative stress caused lipid peroxidation in plant cell membranes. However, addition of 0.25-2.5 mM sulfate alleviated CrVI's toxic effects and decreased TBARS from 23.5 to 9.46-12.3 μmol g(-1) FW. Though CrVI was supplied, 78-96% of CrIII was in the biomass, indicating efficient CrVI reduction to CrIII by P. vittata. The data indicated the amazing ability of P. vittata in Cr uptake at 289 mg kg(-1) h(-1) with little translocation to the fronds. These results indicated that P. vittata had potential in Cr phytoremediation in contaminated sites but further studies are needed to evaluate this potential. The facts that CrVI and sulfate helped each other in uptake by P. vittata suggest that CrVI was not competing with sulfate uptake in P. vittata. However, the mechanisms of how sulfate and CrVI enhance each other's accumulation in P. vittata need further investigation.