Iron plaque

Metal cations in the soil solution may be immobilized by sorption onto iron plaque on root surfaces in submerged soils, in the same way that solubilized Zn + was re-adsorbed on ferric oxide in the experiments in Figure 6.22. Sequestering of metals on the external surfaces of wetland roots in this way limits uptake... 

Otte ML, Rozema 1, Koster L, Haarsma MS, Broekman RA. 1989. Iron plaque in roots of Aster tripolium L. interaction with zinc uptake. New Phytologist 111 309-317. 

Ye ZH, Baker AIM, Wong MH, Willis AJ. 1997a. Copper and nickel uptake, accumulation and tolerance in Typha latifolia with and without iron plaque on the root surface. New Phytologist 136 481-488. 

Chabbi, A. (1999) Juncus bulbosus as a pioneer species in acidic lignite mining lakes interactions, mechanism and survival strategies. NewPhytol. 144 133-142 Chabbi, A. Hines, M.E. Rumpel, C. (2001) The role of organic carbon excretion by bulbous rush roots and its turnover and utilization by bacteria under iron plaques in extremely acid sediments. Environ. Experimental Botany 46 237-245... 

Zhang, X. Zhang, F. Mao, D. (1999) Effect of iron plaque outside roots on nutrient uptake by rice Oryza sativa L.) Phosphate uptake. Plant and Soil 209 187-192 Zhang,Y Charlet, L. Schindler, P.W. (1992) Adsorption of protons, Fe(II) and Al(IIl) on lepidocrocite (y-FeOOH). Colloids Surfaces 63 259-268... 

Reduced to their bare verbal bones, both terms just defined by Pemety prominently appear in one of Duchamp s last ready-mades (MD-196). The immediate function of this minimalist object avant la lettre), inscribed with the artist s monogram M. D., was to serve as a kind of metallic seal set upon the box containing the deluxe edition (32 authorized examples in all) of Robert Lebel s Sur Marcel Duchamp, published the next year to great acclaim. As executed by Duchamp in Paris during the summer of 1958, this is simplicity itself a deep blue, enameled metal (iron) plaque, measuring 15 X 20 cm., which bears an inscription, the kind once familiar to Parisians, neatly laid out in white letters (sans serif). This object, which Jean Clair calls a Ready-made imite, exactly simulates the kind of announcements one formerly saw, a century ago, posted on newly erected apartment buildings. The statement it bears is concise, to say the least ... 

St-Cyr, L., D. Fortin, and Campbell, P.G.C. (1993) Microscopic examination of the iron plaque of a submerged aquatic plant (Vallisneria Americana Michx), Aquatic Botany 46, 155-167. 

Figure 7.10. Concentration-dependent kinetics of arsenate uptake in rice (Oryza sativa) roots with (closed symbols) and without iron plaque (open symbols). The curves are fitted to Michaelis-Menten kinetics, with a poor fit with iron plaque. (Adapted from Chen et al., 2005.)...

Chen, Z., Zhu, Y. G., Liu, W. J., and Meharg, A. A. (2005). Direct evidence showing the effect of root surface iron plaque on arsenite and arsenate uptake into rice (Oryza sativa) roots. New Phytol. 165, 91-97. 

Greipsson, S. (1995). Effect of iron plaque on roots of rice on growth of plants in excess zinc and accumulation of phosphorus in plants in excess copper or nickel. J. Plant. Nutr. 18, 1659-1665. 

Liu, W.-J., Zhu, Y.-G., Smith, F. A., and Smith, S. E. (2004b). Do iron plaque and genotypes affect aisenate uptake and translocation by rice seedlings Oryza sativa L.) grown in solution culture J. Exp. Bot. 55, 1707-1713. 

Taylor GJ, Crowder AA (1984) Formation and morphology of an iron plaque on the roots of Typha latifolia... 

The dominant and most reported component of root plaques is various oxidized compounds of iron. Microscopic observations of root plaques show a highly heterogenous morphology composed mostly of an amorphous material dispersed throughout nodules (50-300 nm in diameter), needles (50-100 nm in length), and filaments with variable lengths. This iron plaque formation on roots results from diffusion of Fe + toward the root zone in response to concentration gradients at the interface (similar to those observed at the soil-floodwater interface). The oxidized rhizosphere functions as a sink for Fe + and other reduced substances. 

Oxidized root channels have been observed for few species, including rice (0. saliva), cattails, reeds, Spartina sp., Carex sp., and Potomogeton sp. (see review by Mendelssohn et al., 1995). The iron-em-iched plaques essentially consist of FeOOH minerals (Bacha and Hossner, 1977). Iron plaque may be amorphous or crystalline, in the forms of iron such as ferric hydroxides, goethite, lepidocrocite, and siderite. Iron oxides or hydroxides in rhizosphere have high affinity for metals and metalloids. 

Soluble Fe(ll) and Mn(II) are oxidized and precipitated on root surfaces, resulting in plaque formation. Although the actual site for Fe(II) and Mn(ll) oxidation in the root zone varies with plant species, the plaque formation typically follows oxygen release from roots. Details of plaque formation in the root zone of wetland plants are discussed in Chapter 7. In this section, consequences of root plaque formation will be discussed. Factors controlling iron plaque formation on roots have been reviewed in detail by Mendelssohn et al. (1995). Plaque on root surfaces can have both positive and negative effects on plants. These include... 

The oxidation and precipitation of reduced Fe(II) and Mn(II) in the root zone (a result of oxygen transport by wetland plants) results in iron and manganese plaque formation on the root surfaces. Iron plaque on root surfaces can protect plants from reduced phytotoxins such as sulfide, but it can also potentially create a barrier limiting nutrient diffusion into the root. 

How is iron plaque formed on the surface of roots of wetland plants List the processes the iron plaque can impact in the root rhizosphere. 

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