Localization of Zinc and Cadmium in Thlaspi caerulescens (Brassicaceae), a Metallophyte that can Hyperaccumulate both Metals

Vázquez, M.D.; Barceló, Juan Antonio; Poschenrieder, Charlotte; Mádico, J.; Hatton, Paul V.; Baker, A. J. M.; Cope, G. H.

doi:10.1016/s0176-1617(11)81091-6

Cited by 213 publications

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“…Estimated errors on R and N are Ϯ 0.01 Å and Ϯ 10% for the first shell, and Ϯ 0.03 Å and Ϯ 20% for the second shell, respectively. Nieden, 2001), similar to T. caerulescens (Vazquez et al, 1992;Kü pper et al, 1999;Frey et al, 2000). Organic acids, including malate, citrate, and oxalate, are primarily located in the vacuoles (Ryan and WalkerSimmons, 1983); thus, are often inferred to chelate metals.…”

Section: Discussionmentioning

confidence: 99%

“…The genetics and the biochemical processes involved in metal uptake, transport, and storage by hyperaccumulating plants are still poorly understood, although this basic information is fundamental for the improvement of the technique (Van Der Lelie et al, 2001). Zn is one of the most important metal contaminant in industrialized countries (Nriagu and Pacyna, 1988), and numerous studies have been conducted on the species Thalspi caerulescens (Vazquez et al, 1992(Vazquez et al, , 1994Pollard and Baker, 1996;Lasat et al, 1998Lasat et al, , 2000Kü pper et al, 1999;Salt et al, 1999;Frey et al, 2000;Assunçaõ et al, 2001) and, to a lesser extent, on Arabidopsis halleri (Macnair et al, 1999;Bert et al, 2000;Kü pper et al, 2000;Zhao et al, 2000). This latter species is of particular interest because it is one of the closest relatives to Arabidopsis (Koch et al, 2001), whose genome is entirely sequenced (Meinke et al, 1998;Kaul et al, 2000).…”

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Forms of Zinc Accumulated in the HyperaccumulatorArabidopsis halleri

et al. 2002

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(M.A.M.) The chemical forms of zinc (Zn) in the Zn-tolerant and hyperaccumulator Arabidopsis halleri and in the non-tolerant and nonaccumulator Arabidopsis lyrata subsp. petraea were determined at the molecular level by combining chemical analyses, extended x-ray absorption spectroscopy (EXAFS), synchrotron-based x-ray microfluorescence, and EXAFS. Plants were grown in hydroponics with various Zn concentrations, and A. halleri specimens growing naturally in a contaminated site were also collected. Zn speciation in A. halleri was independent of the origin of the plants (contaminated or noncontaminated) and Zn exposure. In aerial parts, Zn was predominantly octahedrally coordinated and complexed to malate. A secondary organic species was identified in the bases of the trichomes, which contained elevated Zn concentrations, and in which Zn was tetrahedrally coordinated and complexed to carboxyl and/or hydroxyl functional groups. This species was detected thanks to the good resolution and sensitivity of synchrotron-based x-ray microfluorescence and EXAFS. In the roots of A. halleri grown in hydroponics, Zn phosphate was the only species detected, and is believed to result from chemical precipitation on the root surface. In the roots of A. halleri grown on the contaminated soil, Zn was distributed in Zn malate, Zn citrate, and Zn phosphate. Zn phosphate was present in both the roots and aerial part of A. lyrata subsp. petraea. This study illustrates the complementarity of bulk and spatially resolved techniques, allowing the identification of: (a) the predominant chemical forms of the metal, and (b) the minor forms present in particular cells, both types of information being essential for a better understanding of the bioaccumulation processes.Metal tolerant plants have the ability to survive and reproduce on soils containing high concentrations of metals in forms that are toxic or inimical to other plants (Macnair and Baker, 1994). Metalhyperaccumulating plants have the additional property of storing large amounts of metals in their aerial parts, more than typically 10,000 g g Ϫ1 dry weight for zinc (Zn;Baker and Walker, 1990). This characteristic makes hyperaccumulators highly suitable for phytoremediation, a soft method in which plants are used for the cleanup of metal-polluted soils (Brooks, 1998;Baker et al., 2000). The genetics and the biochemical processes involved in metal uptake, transport, and storage by hyperaccumulating plants are still poorly understood, although this basic information is fundamental for the improvement of the technique (Van Der Lelie et al., 2001). Zn is one of the most important metal contaminant in industrialized countries (Nriagu and Pacyna, 1988), and numerous studies have been conducted on the species Thalspi caerulescens (Vazquez et al., 1992(Vazquez et al., , 1994Pollard and Baker, 1996;Lasat et al., 1998Lasat et al., , 2000Kü pper et al., 1999;Salt et al., 1999;Frey et al., 2000;Assunçaõ et al., 2001) and, to a lesser extent, on Arabidopsis halleri (Macnair et al., 1999;Bert e...

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Section: Discussionmentioning

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Forms of Zinc Accumulated in the HyperaccumulatorArabidopsis halleri

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“…Principally, the methods to study on the bioavailability of trace elements in soils should be analogous to the uptake of metals by biota and need a detailed knowledge of biological uptake mechanisms, particularly the transport of metals through the biological membrane (Town, 2000). In order to achieve these goals, many efforts should be made in the future to understand what speciation of metals present in a sample (Kaneta et al, 1986;Kot and Namiesnik, 2000), where the different forms of metals are localized in plants (Vazquez et al, 1992;Kramer et al, 1996;Kelley et al, 1999), how the different compounds of metals enter the plants apoplastically or intercellularly (Kramer et al, 1997;Salt and Kramer, 2000). Due to the extremely complicated mechanisms involved between the speciation of metals and their bioavailability, at the present time, various empirical approaches are often used to study the speciations of trace elements in soils and the contents of those elements in plants, including single regression (Randall et al, 1976;LeClaire et al, 1984;Chlopecka and Adriano, 1996) and multiple regression analyses (Davies, 1992;Maiz et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

Comparison between fractionation and bioavailability of trace elements in rhizosphere and bulk soils

2002

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Rhizosphere is a microbiosphere and has quite different chemical, physical and biological properties from bulk soils. A greenhouse experiment was performed to compare the difference of fractionation and bioavailability of trace elements Cr, Ni, Zn, Cu, Pb and Cd between rhizosphere soil and bulk soil. In the meantime, the influence of air-drying on the fractionation and bioavailability was also investigated by using wet soil sample as a control. Soils in a homemade rhizobox were divided into four zones: rhizosphere, near rhizosphere, near bulk soil and bulk soil zones, which was designated as S 1 , S 2 , S 3 and S 4 . Elemental speciations were fractionated to water soluble, exchangeable and carbonate bound (B1), Fe-Mn oxide bound (B2), and organic and sulfide bound (B3) by a sequential extraction procedure. Speciation differences were observed for elements Cr, Ni, Zn, Cu, Pb and Cd between the rhizosphere and bulk soils, and between the air-dried and wet soils as well. The concentrations of all six heavy metals in fraction B1 followed the order of S 2 > S 3 > S 1 > S 4 and for B2, the order was S 2 > S 3 % S 4 > S 1 . For B3, the order was S 1 > S 3 % S 4 > S 2 , while for Cd the order was S 2 > S 3 % S 4 > S 1 . The air-drying increased elemental concentration in fractions B1 and B2 by 20-50% and decreased in fraction B3 by about 20-100%. Correlation analysis also indicated that the bioavailability correlation coefficient of fraction B1 in rhizosphere wet soil to plants was better than that between either air-dried or nonrhizosphere soils. Therefore, application of rhizosphere wet soils should be recommended in the future study on the speciation analysis of trace elements in soils and bioavailability. Ó

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“…In T. caerulescens, Cd has been found in the apoplast and in the vacuole (Vázquez et al, 1992). It has been demonstrated that the physiological mechanism of Cd tolerance is not based on an enhanced synthesis of phytochelatins (Ebbs et al, 2002;Schat et al, 2002) but on a preferential compartmentation of the metal in the plant.…”

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Hyperaccumulation of Cadmium and Zinc in Thlaspi caerulescens and Arabidopsis halleri at the Leaf Cellular Level

2004

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Vacuolar compartmentalization or cell wall binding in leaves could play a major role in hyperaccumulation of heavy metals. However, little is known about the physiology of intracellular cadmium (Cd) sequestration in plants. We investigated the role of the leaf cells in allocating metal in hyperaccumulating plants by measuring short-term 109 Cd and 65 Zn uptake in mesophyll protoplasts of Thlaspi caerulescens "Ganges" and Arabidopsis halleri, both hyperaccumulators of zinc (Zn) and Cd, and T. caerulescens "Prayon," accumulating Cd at a lower degree. The effects of low temperature, several divalent cations, and pre-exposure of the plants to metals were investigated. There was no significant difference between the MichaelisMenten kinetic constants of the three plants. It indicates that differences in metal uptake cannot be explained by different constitutive transport capacities at the leaf protoplast level and that plasma and vacuole membranes of mesophyll cells are not responsible for the differences observed in heavy metal allocation. This suggests the existence of regulation mechanisms before the plasma membrane of leaf mesophyll protoplasts. However, pre-exposure of the plants to Cd induced an increase in Cd accumulation in protoplasts of "Ganges," whereas it decreased Cd accumulation in A. halleri protoplasts, indicating that Cd-permeable transport proteins are differentially regulated. The experiment with competitors has shown that probably more than one single transport system is carrying Cd in parallel into the cell and that in T. caerulescens "Prayon," Cd could be transported by a Zn and Ca pathway, whereas in "Ganges," Cd could be transported mainly by other pathways.Cadmium (Cd) and zinc (Zn) are two widespread harmful heavy metals, but there is no cost-effective mean to remove them from the soil. Although phytoextraction using hyperaccumulator plants is seen as a promising technique, a lack of understanding of the basic physiological, biochemical, and molecular mechanisms involved in heavy metal hyperaccumulation prevents the optimization of the phytoextraction technique and its further commercial application. Therefore, a research priority is to gain basic information on the dynamics of metal movement into the cells, their final allocation, and their sink capacities in hyperaccumulating species.Thlaspi caerulescens and Arabidopsis halleri are both plants able to hyperaccumulate Zn and Cd (Robinson et al., 1998; Bert et al., 2000). In T. caerulescens, Zn seems to be sequestrated preferentially in vacuoles of epidermal cells in a soluble form (Kü pper et al., 1999; Frey et al., 2000). In A. halleri leaves, Zn was found to be predominantly coordinated to malate (Sarret et al., 2002) and accumulated in the mesophyll cells (Kü pper et al., 2000;Zhao et al., 2000). An important trait of hyperaccumulating species might be enhanced translocation of the absorbed metal to the shoot. Time course studies of Zn accumulation revealed that T. caerulescens exhibited a 10-fold greater Zn translocation to the shoot a...

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Localization of Zinc and Cadmium in Thlaspi caerulescens (Brassicaceae), a Metallophyte that can Hyperaccumulate both Metals

Cited by 213 publications

References 16 publications

Forms of Zinc Accumulated in the HyperaccumulatorArabidopsis halleri

Forms of Zinc Accumulated in the HyperaccumulatorArabidopsis halleri

Comparison between fractionation and bioavailability of trace elements in rhizosphere and bulk soils

Hyperaccumulation of Cadmium and Zinc in Thlaspi caerulescens and Arabidopsis halleri at the Leaf Cellular Level

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