Deposition of Zinc Phytate in Globular Bodies in Roots of Deschampsia caespitosa Ecotypes; a Detoxification Mechanism?

Steveninck, R. F. M. Van; Steveninck, M. E. Van; Fernando, Denise R.; Horst, W. J.; Marschner, H.

doi:10.1016/s0176-1617(87)80164-5

Cited by 77 publications

(33 citation statements)

References 22 publications

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“…Earlier, Krotz et al (9) showed that after 3 to 4 d exposure of Datura cultured cells to 30 to 45 AM Cd most of the metal was recovered in isolated vacuoles. A number of studies using electron microscopy techniques have shown the presence of Cd deposits in vacuoles as well as other sites within tissues of plants exposed to high levels of Cd (5,19,25,26). Thus, available evidence suggests that, at least after exposure to moderate or high levels of Cd for periods of days, both metals and induced Cdpeptides are likely to be found in the vacuole.…”

Section: Methodsmentioning

confidence: 99%

“…Various mechanisms have been proposed to account for the accumulation of these potentially toxic heavy metal ions in the plant vacuole (18,30). In general, these mechanisms include formation of soluble metal-organic acid complexes (4,9,14) or metal-phytate (25,26), formation ofmetalpeptide or metal-peptide-sulfide complexes (9,18,27), or precipitation of metal-sulfides (2,21,25).…”

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confidence: 99%

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Computer-Simulated Evaluation of Possible Mechanisms for Quenching Heavy Metal Ion Activity in Plant Vacuoles

Wang¹,

Evangelou²,

Nielsen³

et al. 1991

Plant Physiol.

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Various mechanisms have been suggested for the quenching of Cd ion activity in plant vacuoles. These include solution complexation with organic acids and sulfhydryl-containing peptides and precipitation as sulfides. Because direct experimental support for these mechanisms is lacking and difficult to obtain, we have used a computer model to evaluate the quenching role of possible organic and inorganic ligands of tobacco cultured cells exposed to Cd. Results of this thermodynamic evaluation, which assumes that a chemical equilibrium state is met in the vacuole, support the conclusion that sulfhydryl-containing peptides and certain organic acids may form soluble Cd complexes. Although complexation of malate and oxalate with Cd is predicted to be less significant, citrate in the concentration range encountered in the tobacco cultured cell vacuoles has high potential for forming soluble complexes with Cd over the entire possible vacuolar pH range, especially 4.3 to 7.0, even in the presence of low levels of Cd-binding peptides. In addition, results show that inorganic chloride, sulfide (if present), and phosphate may also act to sequester Cd ion activity in the vacuole by forming soluble Cd-Cl and insoluble CdS and Cd-phosphate.Understanding the fate ofCd in plants is of interest because of concerns of Cd transfer from plants to animals and man. Recent studies suggest that heavy metals accumulated in the higher plant are mainly compartmentalized in the vacuole (5, 7, 9, 27). Various mechanisms have been proposed to account for the accumulation of these potentially toxic heavy metal ions in the plant vacuole (18,30). In general, these mechanisms include formation of soluble metal-organic acid complexes (4, 9, 14) or metal-phytate (25, 26), formation ofmetalpeptide or metal-peptide-sulfide complexes (9, 18, 27), or precipitation of metal-sulfides (2,21,25).Support for a particular mechanism of accumulation/sequestration of an ion is gained if the compartment of accumulation/sequestration is verified and if speciation of the ion in that compartment is determined. Both direct and indirect approaches (10) used to determine compartmentation ofions, including heavy metals, can only provide qualitative and quantitative estimates of vacuole contents (28). They cannot identify the species of ion complexes occurring in vacuoles. Therefore, mechanisms proposed on the basis of compartmentation analysis alone are not sufficient to argue the validity of a mechanism of accumulation/sequestration. However, it is possible with computer assistance to simulate the ion species distribution in the plant vacuole and thus to evaluate a proposed mechanism.Computer calculations have been used to model the chemistry of xylem sap of soybean and tomato (29). Here, we use data obtained previously regarding sap composition of vacuoles from Cd-treated tobacco (Nicotiana tabacum) cultured cells and the GEOCHEM-PC computer model (16,23) to predict ion species of these vacuoles in vivo. The prediction of ion speciation in vacuoles of Zn-treate...

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Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

Computer-Simulated Evaluation of Possible Mechanisms for Quenching Heavy Metal Ion Activity in Plant Vacuoles

Wang¹,

Evangelou²,

Nielsen³

et al. 1991

Plant Physiol.

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“…In the Zn hyperaccumulator plant Thlaspi caerulescens , tolerance to high levels of Zn is achieved by sequestering Zn into vacuoles (Lasat et al, 2000). This sequestration appears to be aided by the complexing of Zn with phytic acid, as shown by the formation of Zn-phytin crystals in the vacuoles of root cortical cells of the Zn-tolerant plant Deschampsia caespitosa grown in the presence of high concentrations of Zn (Van Steveninck et al, 1987). High rates of Zn transport across the tonoplast also have been shown to be essential for Zn detoxification in the Zn-tolerant plant Silene vulgaris (Verkleij et al, 1998).…”

Section: The Chalazal Endosperm May Store Mn-and Zn-phytates In Specimentioning

confidence: 99%

Developing Seeds of Arabidopsis Store Different Minerals in Two Types of Vacuoles and in the Endoplasmic Reticulum

2002

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Mineral-accumulating compartments in developing seeds of Arabidopsis were studied using high-pressure-frozen/ freeze-substituted samples. Developing seeds store minerals in three locations: in the protein storage vacuoles of the embryo, and transiently in the endoplasmic reticulum (ER) and vacuolar compartments of the chalazal endosperm. Energy dispersive x-ray spectroscopy and enzyme treatments suggest that the minerals are stored as phytic acid ( myoinositol-1,2,3,4,5,6-hexa kis phosphate) salts in all three compartments, although they differ in cation composition.

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“…Most studies have identified the apoplastic transport mechanism. This is because the accumulation of Ni, Zn and Cd is found mainly in cell walls, residing on the outside of the plasma membrane of epidermal, cortical and endodermal cells up to the Casparian band [9][10][11][12][13][14][15][16]. At the same time, such accumulation is completely absent from stele [10].…”

Section: Introductionmentioning

confidence: 99%

Accumulation and uptake of light rare earth elements in a hyperaccumulator Dicropteris dichotoma

et al. 2003

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Dicropteris dichotoma, a natural perennial fern, grows in acidic soil in southern China. It hyperaccumulates several light rare earth elements La, Ce, Pr and Nd (LREEs) up to about 0.7% of its dry leaf biomass. Through electron microscopic and X-ray microanalyses, LREEs deposits were observed in the cell wall, intercellular space, plasmalemma, vesicles and vacuoles of the root endodermis and stele cells but not in the Casparian band of the fern adventitious root. In addition, LREE deposits were observed in the phloem and xylem of the fern rhizome. These results indicate that at least a portion of the LREEs can be transported symplastically. Histidine and organic acids appear to play a role in stimulating the accumulation of LREEs. This was evident in ferns cultivated in soil amended by histidine, malic and citric acids over a 60-day period. Concentrations of LREEs in D. dichotoma leaves increased by 21-78% as opposed to control, which only increased by 6-10%. While this suggests that histidine and organic acids promote the uptake and sequestration of LREEs in D. dichotoma, the enhancement mechanism of each acid appears to differ. Histidine promoted sequestration of LREEs by forming complexes with LREEs in cells. Organic acids, however, increased the release of LREE from soil, and the uptake of LREEs by fern roots. Most of the LREEs (81-89%) in the cell wall are the result of one of these mechanisms involved in LREE hyperaccumulation. Mass analysis indicated that the molecular weight of LREE-binding peptides was approximately 2000.

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Deposition of Zinc Phytate in Globular Bodies in Roots of Deschampsia caespitosa Ecotypes; a Detoxification Mechanism?

Cited by 77 publications

References 22 publications

Computer-Simulated Evaluation of Possible Mechanisms for Quenching Heavy Metal Ion Activity in Plant Vacuoles

Computer-Simulated Evaluation of Possible Mechanisms for Quenching Heavy Metal Ion Activity in Plant Vacuoles

Developing Seeds of Arabidopsis Store Different Minerals in Two Types of Vacuoles and in the Endoplasmic Reticulum

Accumulation and uptake of light rare earth elements in a hyperaccumulator Dicropteris dichotoma

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