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Heavy-Metal Accumulation by Citrus Roots

Paul F. Smith
Botanical Gazette
Vol. 114, No. 4 (Jun., 1953), pp. 426-436
Stable URL: http://www.jstor.org/stable/2472504
Page Count: 11
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Heavy-Metal Accumulation by Citrus Roots
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Abstract

1. Various short-term experiments on the accumulation of heavy-metal ions by citrus roots are described. 2. Copper, zinc, iron, and manganese appear to be accumulated by roots from mildly acidic solutions through nonvital processes. Thus in matched samples of seedlings, half of which had the roots killed in boiling water, accumulation of these metals was essentially identical. 3. For some unknown reason, roots first allowed to adsorb Zn, Mn, or Fe were then found to adsorb more Cu than roots without this pretreatment. The other metals were not similarly affected when the order of adsorption was reversed. At the relatively low levels of saturation obtaining in these experiments, the adsorption of Cu, Zn, or Mn did not displace an appreciable amount of a previously adsorbed metal, but Cu was displaced by Fe, particularly when the latter was supplied as a chelated complex molecule. 4. In short-term tests there was little evidence that an adsorbed metallic ion repressed the adsorption of a second metal. Such repressive action was apparent, however, when two or more elements were in the same solution. Chelated Fe was particularly effective in reducing Cu adsorption. Copper, in turn, interfered somewhat with Mn adsorption. 5. Copper accumulation by citrus roots appears to be directly related to the nonreplaceable protein nitrogen of the root. 6. Color reactions showed that the bulk of the cortex is involved in the accumulation of these elements. The innermost layer, the endodermis, appeared to have the highest concentration of both Cu and Zn. 7. Apparently, the mechanism involved in the adsorption of these elements by plant roots is not entirely dissimilar to that of soil colloids where cations are held by polar linkages.

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