砷超富集植物蜈蚣草原生质体的分离及其抗砷性分析

蜈蚣草(Pteris vittata)是一种砷超富集植物, 能够通过根从土壤中吸收砷, 并将其输送至羽叶中富集。为了探索蜈蚣草单个细胞在砷积累和砷抗性中的特性, 本文首次通过酶解方法获得了这一砷超富集蕨类植物的原生质体, 并研究了原生质体在不同浓度砷胁迫下的生活力。结果显示, 蜈蚣草原生质体的抗砷性远高于烟草原生质体的抗砷性, 与其整体植株的抗性一致。这为探索砷抗性和超富集机理提供了一个新的研究体系。     

蜈蚣草砷超富集机制及其在砷污染修复中的应用

蕨类植物蜈蚣草能够从土壤中吸收砷,并储存于地上部分羽叶的液泡中。蜈蚣草具有高效的抗氧化系统,以降低砷的毒害;其砷酸还原系统和液泡区隔化是蜈蚣草进行砷解毒和砷超富集的重要机制。本文综述了目前蜈蚣草砷超富集机制研究的主要进展,并对其在修复砷污染环境的应用中进行了讨论。     

蜈蚣草中砷超富集的分子机制研究进展

砷是一种毒性很强的类金属元素,土壤砷污染可引发一系列食品安全问题,进而威胁人类健康。蜈蚣草具有极强的富集砷的能力,在砷污染土壤的植物修复中具有重要的应用价值。深入阐释蜈蚣草超富集砷的分子机制是植物修复技术的核心理论基础。文中综述了蜈蚣草超富集砷的组学研究进展,以及目前鉴定到的砷富集过程中的重要分子元件,并对未来的研究方向和趋势进行了展望。     

大叶井口边草——一种新发现的富集砷的植物

自 1 999年以来对位于湖南省一些高砷区的植物和土壤进行了一系列的野外调查 ,以着力寻找砷的超富集植物。结果表明 ,与砷超富集植物蜈蚣草同属的另一种植物——大叶井口边草 ,对砷也具有显著的富集特征。这一发现为研究揭示砷在植物中的超富集机理提供了一种新的材料。建议深入开展蜈蚣草与大叶井口边草这两种砷富集植物的对比研究。     

大叶井边草——一种新发现的富集砷的植物

自1999年以来对位于湖南省一些高砷区的植物和土壤进行了一系列的野外调查,以着力寻找砷的超富集植物。结果表明,与砷超富集植物蜈蚣草同属的另一种植物－－大叶井口边草,对砷也具有显著的富集特征。这一发现为研究揭示砷在植物中的超富集机理提供了一种新的材料,建议深入开展蜈蚣草与大叶井口边草这两种砷富集植物的对比研究。     

蜈蚣草毛状体对砷的富集作用及其意义

利用配备EDX的环境扫描电子显微镜等手段研究了蜈蚣草羽叶的微形态及砷元素在蜈蚣草中的微区分布. 结果表明, 在羽叶的正反表皮观察到大量的毛状体, 其结构为多细胞组成, 呈匍匐状, 平均长度为160 μm, 平均直径28 μm. X射线能谱分析表明, 在加砷处理中, 蜈蚣草的表皮、羽叶毛状体存在有明显的砷峰, 并且毛状体中砷的含量分别为表皮细胞与叶肉细胞的2.4, 3.9倍, 在同一毛状体中, 帽细胞中的砷含量较低, 而在节细胞和基细胞中的砷含量较高. 这一发现为揭示蜈蚣草富集砷和耐砷毒的机理提供了新的线索.     

不同生态型摩西球囊霉菌株对蜈蚣草砷吸收的影响

砷超富集植物——蜈蚣草无论是在野外或是在室内均能被丛枝菌根真菌(AM真菌)侵染,但其对蜈蚣草砷吸收及转运的机理尚不清晰.本研究将分离于湖南省郴州市金川塘某铅锌尾矿蜈蚣草根际土壤(Glomus mosseae BGC GD01,简称污染菌株)和云南省未污染土壤(G.mosseae BGC YN05,简称非污染菌株)的2种摩西球囊霉菌株分别接种于非污染生态型和污染生态型蜈蚣草根际,8周后利用菌根化蜈蚣草幼苗在浓度为100 μmol·L-1砷(Na2HAsO4·7H2O)营养液中进行为期24 h的水培试验.结果表明,2种生态型摩西球囊霉菌株分别与蜈蚣草形成中等程度侵染,侵染率为25.2％ ～31.3％.无论是接种污染菌株或是非污染菌株,均明显促进了蜈蚣草根部对磷的吸收.在24 h水培试验期间,接种非污染菌株显著促进了蜈蚣草根部砷的吸收,但接种污染菌株对蜈蚣草根部砷吸收的促进作用有限,说明AM真菌对蜈蚣草砷吸收存在种内差异.     

富砷植物蜈蚣草孢子和配子体发育的显微观察

蜈蚣草(Pteris vittata L.)隶属于凤尾蕨科( Pteridaceae),是钙质土及石灰岩的指示植物,分布于我国热带和亚热带[1],是常见的蕨类植物.蜈蚣草是最先被发现的As超富集植物,它的叶片是主要的富集部位[2],所以,蜈蚣草可用来修复砷污染的土壤,由此使它受到人们的广泛关注.     

砷对土壤-蜈蚣草系统中磷生物有效性的影响

磷是植物必需的大量营养元素,而其同族元素砷却不是植物生长发育所必需的。通过等温吸附平衡实验发现土壤中存在的砷可以降低褐土对磷的吸附,褐土对砷的吸附率大于等于褐土对磷的吸附率。对砷超富集植物蜈蚣草而言,土壤中砷的添加量不超过800mg／kg时,蜈蚣草地上部和地下部磷含量显著提高,结果初步表明,砷可以提高土壤中磷的生物有效性。     

刈割对蜈蚣草的砷吸收和植物修复效率的影响

以野生苗移栽的蜈蚣草为试材 ,通过盆栽试验研究了收获次数对蜈蚣草生长、砷吸收和植物修复效率的影响。结果表明 :在 3次收获中 ,随着收获次数的增加 ,不同砷浓度处理之间蜈蚣草生物量的差异逐步缩小 ;不加砷的对照处理中 ,每次收获后的砷吸收速率下降趋势 ,而在 3个加砷处理中 ,第 2次收获和第 3次收获的蜈蚣草的吸砷速率为 6 3～ 75 μg/ (plant· d)、4 4～ 5 5μg/ (plant· d) ,均显著高于第 1次收获时的吸收速率。表明多次收获并没有降低砷的积累速度。由此可见 ,通过适当增加蜈蚣草的收获次数是提高砷修复效率的一种策略     

The potential of Thelypteris palustris and Asparagus sprengeri in phytoremediation of arsenic contamination

The potential of two plants, Thelypteris palustris (marsh fern) and Asparagus sprengeri (asparagus fern), for phytoremediation of arsenic contamination was evaluated. The plants were chosen for this study because of the discovery of the arsenic hyperaccumulating fern, Pteris vittata (Ma et al., 2001) and previous research indicating asparagus fern's ability to tolerate > 1200 ppm soil arsenic. Objectives were (1) to assess if selected plants are arsenic hyperaccumulators; and (2) to assess changes in the species of arsenic upon accumulation in selected plants. Greenhouse hydroponic experiments arsenic treatment levels were established by adding potassium arsenate to solution. All plants were placed into the hydroponic experiments while still potted in their growth media. Marsh fern and Asparagus fern can both accumulate arsenic. Marsh fern bioaccumulation factors (> 10) are in the range of known hyperaccumulator, Pteris vittata Therefore, Thelypteris palustris is may be a good candidate for remediation of arsenic soil contamination levels of < or = 500 microg/L arsenic. Total oxidation of As (III) to As (V) does not occur in asparagus fern. The asparagus fern is arsenic tolerant (bioaccumulation factors < 10), but is not considered a good potential phytoremediation candidate.     

The Role of Metal Transport and Tolerance in Nickel Hyperaccumulation by Thlaspi goesingense Halacsy

Metal hyperaccumulators are plants that are capable of extracting metals from the soil and accumulating them to extraordinary concentrations in aboveground tissues (greater than 0.1% dry biomass Ni or Co or greater than 1% dry biomass Zn or Mn). Approximately 400 hyperaccumulator species have been identified, according to the analysis of field-collected specimens. Metal hyperaccumulators are interesting model organisms to study for the development of a phytoremediation technology, the use of plants to remove pollutant metals from soils. However, little is known about the molecular, biochemical, and physiological processes that result in the hyperaccumulator phenotype. We investigated the role of Ni tolerance and transport in Ni hyperaccumulation by Thlaspi goesingense, using plant biomass production, evapotranspiration, and protoplast viability assays, and by following short- and long-term uptake of Ni into roots and shoots. As long as both species (T. goesingense and Thlaspi arvense) were unaffected by Ni toxicity, the rates of Ni translocation from roots to shoots were the same in both the hyper- and nonaccumulator species. Our data suggest that Ni tolerance is sufficient to explain the Ni hyperaccumulator phenotype observed in hydroponically cultured T. goesingense when compared with the Ni-sensitive nonhyperaccumulator T. arvense.     

Arabis gemmifera is a hyperaccumulator of Cd and Zn

Hyperaccumulators are essential for phytoremediation of heavy metals. In Europe and North America, many studies have been conducted to find more effective plants for phytoremediation of various pollutants. In Japan, this field of research has just recently come more into focus. A type of fern in Japan, Athyrium yokoscense, is well known as a hyperaccumulator of Cd and Zn. However, it is not suitable for phytoremediation because it is a summer green and grows slowly. Therefore, in order to find hyperaccumulators other than from A. yokoscense, we surveyed plants growing at polluted sites in Japan. We found that the Brassicae Arabis gemmifera is a hyperaccumulator of Cd and Zn, with phytoextraction capacities almost equal to Thlaspi caerulescens.     

Tolerance of Landoltia punctata to arsenate: an evaluation of the potential use in phytoremediation programs

Abstract

Plants used in phytoremediation should accumulate and tolerate a specific pollutant. Here, we aimed at evaluating a possible arsenic (As) accumulation and mechanisms of tolerance against As-induced damage in Landoltia punctata to explore this species for phytoremediation. Plants were subjected to increasing As levels. As absorption was higher with increasing As levels. The activity of superoxide dismutase and glutathione reductase as well as anthocyanin levels increased with As levels. Catalase and peroxidase activities increased in plants subjected to As levels up to 1.0?mg L^?1 and decreased at higher levels. Due to the antioxidant system, higher levels of reactive oxygen species were restrained in plants under low levels of As. However, the levels of superoxide anion, hydrogen peroxide, and lipid peroxidation increased in response to the impaired antioxidant system induced by the highest As levels. Biomass decreased in plants exposed to As and scanning electron microscopy revealed root structural damage in the root cap of plants under 3.0?mg L^?1?As. This work highlights that L. punctata can be considered a hyperaccumulator species and has potential for As phytoremediation when levels are lower than 1.0?mg L^?1—a concentration 100-fold higher than that recommended for drinking water.

Novelty Statement: Landoltia punctata can be considered a hyperaccumulator species and has the potential for arsenic phytoremediation when levels are lower than 1.0?mg L^?1.     

Arsenic hyperaccumulation in gametophytes of Pteris vittata. A new model system for analysis of arsenic hyperaccumulation

The sporophyte of the fern Pteris vittata is known to hyperaccumulate arsenic (As) in its fronds to >1% of its dry weight. Hyperaccumulation of As by plants has been identified as a valuable trait for the development of a practical phytoremediation processes for removal of this potentially toxic trace element from the environment. However, because the sporophyte of P. vittata is a slow growing perennial plant, with a large genome and no developed genetics tools, it is not ideal for investigations into the basic mechanisms underlying As hyperaccumulation in plants. However, like other homosporous ferns, P. vittata produces and releases abundant haploid spores from the parent sporophyte plant which upon germination develop as free-living, autotrophic haploid gametophyte consisting of a small (<1 mm) single-layered sheet of cells. Its small size, rapid growth rate, ease of culture, and haploid genome make the gametophyte a potentially ideal system for the application of both forward and reverse genetics for the study of As hyperaccumulation. Here we report that gametophytes of P. vittata hyperaccumulate As in a similar manner to that previously observed in the sporophyte. Gametophytes are able to grow normally in medium containing 20 mm arsenate and accumulate >2.5% of their dry weight as As. This contrasts with gametophytes of the related nonaccumulating fern Ceratopteris richardii, which die at even low (0.1 mm) As concentrations. Interestingly, gametophytes of the related As accumulator Pityrogramma calomelanos appear to tolerate and accumulate As to intermediate levels compared to P. vittata and C. richardii. Analysis of gametophyte populations from 40 different P. vittata sporophyte plants collected at different sites in Florida also revealed the existence of natural variability in As tolerance but not accumulation. Such observations should open the door to the application of new and powerful genetic tools for the dissection of the molecular mechanisms involved in As hyperaccumulation in P. vittata using gametophytes as an easily manipulated model system.     

Impact of mycorrhization on the abundance,growth and leaf nutrient status of ferns along a tropical elevational gradient

Mycorrhizal fungi are crucial for the ecological success of land plants, providing their hosts with nutrients in exchange for organic C. However, not all plants are mycorrhizal, especially ferns, of which about one-third of the species lack this symbiosis. Because the mycorrhizal status is evolutionarily ancestral, this lack of mycorrhizae must have ecological advantages, but what these advantages are and how they affect the competitive ability of non-mycorrhizal plants under natural conditions is currently unknown. To address this uncertainty, we studied terrestrial fern assemblages and species abundances as well as their mycorrhization status, leaf nutrient concentration and relative annual growth along an elevational gradient in the Ecuadorian Andes (500–4,000 m). We surveyed the mycorrhizal status of 375 root samples belonging to 85 species, and found mycorrhizae in 89 % of the samples. The degree of mycorrhization decreased with elevation but was unrelated to soil nutrients. Species with mycorrhizae were significantly more abundant than non-mycorrhizal species, but non-mycorrhizal species had significantly higher relative growth and concentrations of leaf N, P, Mg, and Ca. Our study thus shows that despite lower abundances, non-mycorrhizal fern species did not appear to be limited in their growth or nutrient supply relative to mycorrhizal ones. As a basis for future studies, we hypothesize that non-mycorrhizal fern species may be favoured in special microhabitats of the forest understory with high soil nutrient or water availability, or that the ecological benefit of mycorrhizae is not related to nutrient uptake but rather to, for example, pathogen resistance.     

Arsenic alters uptake and distribution of sulphur in Pteris vittata

Low‐molecular‐weight thiol (LMWT) synthesis has been reported to be directly induced by arsenic (As) in Pteris vittata, an As hyperaccumulator. Sulphur (S) is a critical component of LMWTs. Here, the effect of As treatment on the uptake and distribution of S in P. vittata was investigated. In P. vittata grown under low S conditions, the presence of As in the growth medium enhanced the uptake of SO₄^2?, which was used for LMWT synthesis in fronds. In contrast, As application did not affect SO₄^2? uptake in Nephrolepis exaltata, an As non‐hyperaccumulator. Moreover, the isotope microscope system revealed that S absorbed with As accumulated locally in a vacuole‐like organelle in epidermal cells, whereas S absorbed alone was distributed uniformly. These results suggest that S is involved in As transport and/or accumulation in P. vittata. X‐ray absorption near‐edge structure analysis revealed that the major As species in the fronds and roots of P. vittata were inorganic As(III) and As(V), respectively, and that As–LMWT complexes occurred as a minor species. Consequently, in case of As accumulation in P. vittata, S possibly acts as a temporary ligand for As in the form of LMWTs in intercellular and/or intracellular transport (e.g. vacuolar sequestration).     

Arsenic in the rhizosphere soil solution of ferns

The aim of this study was to explore the evidence of arsenic hyperaccumulation in plant rhizosphere solutions. Six common fern plants were selected and grown in three types of substrate: arsenic (As) -tailings, As-spiked soil, and soil-As-tailing composites. A rhizobox was designed with an in-situ collection of soil solutions to analyze changes in the As concentration and valence as well as the pH, dissolved organic carbon (DOC) and total nitrogen (TN). Arsenite composed less than 20% of the total As, and As depletion was consistent with N depletion in the rhizosphere solutions of the various treatments. The As concentrations in the rhizosphere and non-rhizosphere solutions in the presence of plants were lower than in the respective controls without plants, except for in the As-spiked soils. The DOC concentrations were invariably higher in the rhizosphere versus non-rhizosphere solutions from the various plants; however, no significant increase in the DOC content was observed in Pteris vittata, in which only a slight decrease in pH appeared in the rhizosphere compared to non-rhizosphere solutions. The results showed that As reduction by plant roots was limited, acidification-induced solubilization was not the mechanism for As hyperaccumulation.     

Irrigation of Three Wetland Species and a Hyperaccumlating Fern with Arsenic-Laden Solutions: Observations of Growth,Arsenic Uptake,Nutrient Status,and Chlorophyll Content

Engineered wetlands can be an integral part of a treatment strategy for remediating arsenic-contaminated wastewater, wherein, As is removed by adsorption to soil particles, chemical transformation, precipitation, or accumulation by plants. The remediation process could be optimized by choosing plant species that take up As throughout the seasonal growing period. This report details experiments that utilize wetland plant species native to Ohio (Carex stricta, Pycnanthemum virginianum, and Spartina pectinata) that exhibit seasonally related maximal growth rates, plus one hyperaccumulating fern (Pteris vittata) that was used to compare arsenic tolerance. All plants were irrigated with control or As-laden nutrient solutions (either 0, 1.5, or 25 mg As L^?1) for 52 d. Biomass, nutrient content, and chlorophyll content were compared between plants treated and control plants (n = 5). At the higher concentration of arsenic (25 mg L^?1), plant biomass, leaf area, and total chlorophyll were all lower than values in control plants. A tolerance index, based on total plant biomass at the end of the experiment, indicated C. stricta (0.99) and S. pectinata (0.84) were more tolerant than the other plant species when irrigated with 1.5 mg As L^?1. These plant species can be considered as candidates for engineered wetlands.