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Absorption of chromium and reduction of chromate by subterranean clover
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In order to optimize phytoremediation techniques, it is important to first understand the plant physiological processes associated with enhanced absorption and translocation of the target metal in the plant. The emphasis in the current study is with chromium. The specific objectives were to: (1) determine the oxidation state of chromium in the plant using electron paramagnetic resonance (EPR) spectroscopy and x-ray absorption near edge spectroscopy (XANES), (2) investigate the probable mode of complication in plants grown in different Cr sources by EPR spectroscopy, (3) determine the distribution of Cr in plant tissues using synchrotron x-ray fluorescent (SXRF) microphone spectroscopy, and (4) determine the effect of root plasma membrane bound ferric reductive activity on Cr(VI) absorption. Subterranean clover (Trifolium brachycalvcinum Katzn. and Morley cv. Koala), utilized because of the relatively high tolerance, absorption, and translocation of CrO₄²⁻, was grown hydroponically in a nutrient solution with Cr(III)Cl₃, Cr(III)-oxalate, Cr(III)-citrate, Cr(III)-EDTA or K₂Cr(VI)O₄ at a range of concentrations and exposure times. The uptake and translocation of Cr by the plant was dependent on the form and concentration of Cr supplied. Inorganic sources of Cr(III) precipitated in or on the roots of the plants as Cr(OH)₄. In all cases, Cr predominantly existed in the plant as a Cr(III)-organic complex. There is some indication that Cr(III)-citrate and Cr(III)-oxalate were absorbed by the plant and, in the case of Cr(III)-citrate, translocated to the leaves. At high Cr(VI) treatment concentrations, Cr(VI), Cr(V), and Cr(III) were observed in the roots and Cr(V) and Cr(III) in the shoots. At low concentrations the plant could effectively reduce Cr(VI) to Cr(III), which is an important component of the detoxification mechanism. At low concentrations of Cr(VI), once in the vascular system, Cr was transported as a Cr(III)-organic complex to the leaf margins. At high concentrations of Cr(VI), SXRF microphone imaging revealed higher concentrations of Cr in the leaf veins than at the margin, indicating that Cr translocation to the leaf margin might be limited by Cr toxicity. Iron deficiency enhanced Cr uptake, particularly in the roots, indicating the possible involvement of ferric reductive in Cr uptake and reduction.
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Includes bibliographical references (leaves 103-109).
Issued also on microfiche from Lange Micrographics.
Howe, Julie Ann (1999). Absorption of chromium and reduction of chromate by subterranean clover. Master's thesis, Texas A&M University. Available electronically from
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