Solubility and accumulation of metals in Chinese brake fern, vetiver and rostrate sesbania using chelating agents

Greenhouse experiments were conducted to study the effects of chelating agents on the growth and metal accumulation of Chinese brake fern (Pteris vittata L.), vetiver (Vetiveria zizanioides L.), and rostrate sesbania (Sesbania rostrata L.) in soil contaminated with arsenic (As), Cu, Pb, and Zn. Among the five chelating agents used [ethylenediaminetriacetic acid (EDTA), hydroxyethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid (NTA), oxalic acid (OA), and phytic acid (PA)], OA was the best to mobilize As, EDTA to mobilize Cu and Pb, and HEDTA to mobilize Zn from soil, respectively. The biomass of vetiver was the highest, followed by rostrate sesbania. All chelating agents inhibited the growth of Chinese brake fern and rostrate sesbania, but HEDTA significantly increased the aboveground biomass of vetiver. Dry weights of both Chinese brake fern and rostrate sesbania decreased with increasing EDTA concentrations amended in the soil, especially in treatments with high EDTA concentrations. EDTA and HEDTA enhanced Cu, Zn, and Pb, but lowered As accumulation in all three plant species, except for As in vetiver, while OA significantly enhanced As accumulation in the aboveground part of vetiver. Concentrations of Cu, Zn, and Pb in the aboveground parts of plants increased significantly with the increase of EDTA concentrations and treatment time. In addition to As, Chinese brake fern also accumulated the highest Cu, Pb, and Zn in its aboveground parts among the three plant species grown in metal-contaminated soil with EDTA/HEDTA treatments. This species, therefore, can be used to simultaneously clean up As, Cu, Pb, and Zn from contaminated soils with the aid of EDTA or HEDTA.     

Phytoextraction of arsenic from soil by Leersia oryzoides

The potential of Leersia oryzoides (rice-cut grass) to remediate arsenic-contaminated soil was studied in greenhouse pot experiments. Leersia oryzoides grown in soil amended with arsenic to a concentration of 110 mg kg(-1), extracted up to 305 mg kg(-1) and 272 mg kg(-1) arsenic into its shoots and roots, respectively, giving a shoot:root quotient of 1.12 and phytoextraction coefficients up to 2.8. Plants in the arsenic-amended soil showed visible signs of stress in the first 8 wk of growth, but then recovered. Based on the 132 plants that were grown in a surface area of approximately 180 cm2, the calculated total arsenic taken up by shoots is 120, 130, and 130 g ha(-1) at 6, 10, and 16 wk, respectively, suggesting that additional arsenic could be removed by periodic mowing over a growing season. Extraction with a mixture of nitric acid and hydrogen peroxide indicated that the available arsenic was constant after the first 6 wk. Uptake is comparable to that reported for duckweed (Lemna gibba L.) and overlaps the low end of the values reported for Chinese brake fern (Pteris Vittata L.)     

Selecting appropriate forms of nitrogen fertilizer to enhance soil arsenic removal by Pteris vittata: a new approach in phytoremediation

Certain plant species have been shown to vigorously accumulate some metals from soil, and thus represent promising and effective remediation alternatives. In order to select the optimum forms of nitrogen (N) fertilizers for the arsenic (As) hyperaccumulator, Pteris vittata L., to maximize As extraction, five forms of N were added individually to different treatments to study the effect of N forms on As uptake of the plants under soil culture in a greenhouse. Although shoot As concentration tended to decrease and As translocation from root to shoot was inhibited, overall As accumulation was greater due to higher biomass when N fertilizer was added. Arsenic accumulation in plants with N fertilization was 100-300% more than in the plants without N fertilization. There were obvious differences in plant biomass and As accumulation among the N forms, i.e., NH4HCO3, (NH4)2S04, Ca(NO3)2, KNO3, urea. The total As accumulation in the plants grown in As-supplied soil, under different forms of N fertilizer, decreased as NH4HCO3>(NH4)2S04 > urea > Ca(NO3)2 >KNO3>CK. The plants treated with N and As accumulated up to 5.3-7.97 mg As/pot and removed 3.7-5.5% As from the soils, compared to approximately 2.3% of As removal in the control. NH4+ -N was apparently more effective than other N fertilizers in stimulating As removal when soil was supplied with As at initiation. No significant differences in available As were found among different forms of N fertilizer after phytoremediation. It is concluded that NH4+ -N was the preferable fertilizer for P. vittata to maximize As removal.     

Nerve growth factor prevents arsenic-induced toxicity in PC12 cells through the AKT/GSK-3β/NFAT pathway

The potential risk of arsenic-related neurodegeneration has been a growing concern. Arsenic exposure has been reported to disrupt neurite growth and neuron body integrity in vitro; however, its underlying mechanism remains unclear. Previously, we showed that arsenic sulfide (AS) exerted cytotoxicity in gastric and colon cancer cells through regulating nuclear factor of the activated T cells (NFAT) pathway. The NFAT pathway regulates axon path finding and neural development. Using neural crest cell line PC12 cells as a model, here we show that AS caused mitochondrial membrane potential collapse, reactive oxygen species production, and cytochrome c release, leading to mitochondria-mediated apoptosis via the AKT/GSK-3β/NFAT pathway. Increased glycogen synthase kinase-3 beta (GSK-3β) activation leads to the inactivation of NFAT and its antiapoptotic effects. Through inhibiting GSK-3β activity, both nerve growth factor (NGF) and Tideglusib, a GSK-3β inhibitor partially rescued the PC12 cells from the AS-induced cytotoxicity and restored the expression of NFATc3. In addition, overexpression of NFATc3 stimulated neurite outgrowth and potentiated the effect of NGF on promoting the neurite outgrowth. Collectively, our results show that NFATc3 serves as the downstream target of NGF and plays a key role in preventing AS-induced neurotoxicity through regulating the AKT/GSK-3β/NFAT pathway in PC12 cells.     

Newly Identified Nematodes from Mono Lake Exhibit Extreme Arsenic Resistance

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镉和砷在植物中的积累及其分子调控机制研究进展

植物源食物是人类摄入有毒金属元素镉(Cd)和砷(As)的主要途径。深化植物对Cd和As积累途径分子机制的认识,有助于培育可食部分中低有毒金属元素含量的作物新种质。该文基于近年来有关植物Cd和As积累在主要模式植物中所取得的实质性研究进展,对植物介导Cd和As吸收的转运蛋白、As形态和生物转化机制以及控制Cd和As根-地上部转运效率和分配的关键因子等方面的研究进展进行综述,并对未来的研究前景进行了展望。     

Bacillus sp.ZJS3基因组测序及砷胁迫下相关基因表达分析

【背景】环境中高毒性As³⁺的微生物氧化在砷的生物地球化学循环中起重要作用,具有潜在的应用价值。【目的】Bacillus sp.ZJS3菌株是本实验室前期分离鉴定的一株As³⁺耐受菌株,而且对多种重金属具有耐受性,期望进一步明确该菌株在As³⁺胁迫下菌体形态变化及应对砷胁迫的遗传基础,为As³⁺耐受细菌的研究提供基础数据。【方法】使用单分子实时测序（single-molecule real-time sequencing,SMRT）及Illumina测序技术对Bacillus sp.ZJS3菌株进行全基因组测序,对其基因进行功能注释和生物信息学分析,并结合绝对定量PCR技术对砷抗性及砷代谢相关基因进行分析。【结果】Bacillus sp.ZJS3菌株基因组大小为5.82 Mb,GC含量为35.9%,包含染色体1个、质粒3个、CDS数量为5 981个、tRNA 104个、sRNA 136个、rRNA 42个、串联重复序列173个、基因岛13个、转运蛋白1 023个、跨膜蛋白1 717个和双组分调控基因160个。NR、Swiss-Prot、Pfam、COG、GO和KEGG数据库分别可注释Bacillus sp.ZJS3菌株基因组中97.66%、69.30%、78.52%、65.49%、67.65%和43.87%的基因。绝对定量PCR结果表明,arsC基因在砷处理条件下显著高于对照组,而arsB基因在砷处理条件下显著低于对照组。【结论】Bacillus sp.ZJS3菌株在As³⁺胁迫下可能导致细胞分裂无法正常进行,进而影响细胞形态。基因组中aqpZ、arsA、arsB、arsC等基因的存在表明该菌株具有As³⁺外排和还原As⁵⁺的能力,phoUpstBACS的存在表明菌株可以吸收As⁵⁺,但菌株受到外界环境As³⁺胁迫时arsB表达水平降低。     

A hydrogen-peroxide digestion system for tissue trace-metal analysis

Tissue digestion prior to analysis for trace metals is usually carried out with strong acids. Nitric acid, alone or in combination with perchloric acid, is most commonly used. In addition to the laborious acid washing of all glassware prior to use, the digestion necessitates exposure to potential environmental contamination. Use of perchloric acid mandates a specially constructed hood with facilities for washing to remove acid deposits. A simple digestion procedure using 30% hydrogen peroxide in polyethylene vials in an oven at approximately 75°C has been previously described for the measurement of zinc in tissues using flame or flameless atomic absorption spectrophotometry and of selenium in liver by flameless atomic absorption. Readings for reagent blanks were insignificant. The technique has been further developed with a reduction in digestion time using 50% H₂O₂. Analysis of liver has been extended to include copper, manganese, and arsenic. Although the level of arsenic present was too low to be detected, 50 and 100 ng of this element added to the liver powder was completely recovered. The digest obtained when dissolved in appropriate solvent is suitable for analysis for multiple trace metals. Author to whom all correspondence and reprint requests should be addressed.     

The influence of chemical form and concentration of arsenic on rice growth and tissue arsenic concentration

Arsenic absorption by rice (Oryza sativa, L.) in relation to the chemical form and concentration of arsenic added in nutrient solution was examined. A 4 × 3 × 2 factorial experiment was conducted with treatments consisting of four arsenic chemical forms [arsenite, As(III); arsenate, As(V); monomethyl arsenic acid, MMAA; and dimethyl arsenic acid, DMAA], three arsenic concentrations [0.05, 0.2, and 0.8 mg As L^-1], and two cultivars [Lemont and Mercury] with a different degree of susceptibility to straighthead, a physiological disease attributed to arsenic toxicity. Two controls, one for each cultivar, were also included. Arsenic phytoavailability and phytotoxicity are determined primarily by the arsenic chemical form present. Application of DMAA increased total dry matter production. While application of As(V) did not affect plant growth, both As(III) and MMAA were phytotoxic to rice. Availability of arsenic to rice followed the trend: DMAA<As(V)<MMAA<As(III). Upon absorption, DMAA was readily translocated to the shoot. Arsenic(III), As(V), and MMAA accumulated in the roots. With increased arsenic application rates the arsenic shoot/root concentration decreased for the As(III) and As(V) treatments. Monomethyl arsenic acid (MMAA), however, was translocated to the shoot upon increased application. The observed differential absorption and translocation of arsenic chemical forms by rice is possibly responsible for the straighthead disorder attributed to arsenic.