JXB Advance Access originally published online on September 4, 2007
Journal of Experimental Botany 2007 58(11):2939-2947; doi:10.1093/jxb/erm119
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© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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RESEARCH PAPER |
Cd accumulation in roots and shoots of durum wheat: the roles of transpiration rate and apoplastic bypass
1Department of Land Resource Science, University of Guelph, Guelph, ON, Canada
2Department of Biology, University of Waterloo, Waterloo, ON, Canada
* To whom correspondence should be addressed. E-mail: bhale{at}uoguelph.ca
Cadmium is readily taken up from soils by plants, depending on soil chemistry, and variably among species and cultivars; altered transpiration and xylem transport and/or translocation in the phloem could cause this variation in Cd accumulation, some degree of which is heritable. Using Triticum turgidum var. durum cvs Kyle and Arcola (high and low grain Cd accumulating, respectively), the objectives of this study were to determine if low-concentration Cd exposure alters transpiration, to relate transpiration to accumulation of Cd in roots and shoots at several life stages, and to evaluate the role of apoplastic bypass in the accumulation of Cd in shoots. The low abundance isotope 106Cd was used to probe Cd translocation in plants which had been exposed to elemental Cd or were Cd-naïve; apoplastic bypass was monitored using the fluorescent dye PTS (8-hydroxy-1,3,6-pyrenetrisulphonate). Differential accumulation of Cd by Kyle and Arcola could be partially attributed to the effect of Cd on transpiration, as exposure to low concentrations of Cd increased mass flow and concomitant Cd accumulation in Kyle. Distinct from this, exposure of Arcola to low concentrations of Cd reduced translocation of Cd from roots to shoots relative to root accumulation of Cd. It is possible, but not tested here, that sequestration mechanisms (such as phytochelatin production, as demonstrated by others) are the genetically controlled difference between these two cultivars that results in differential Cd accumulation. These results also suggest that apoplastic bypass was not a major pathway of Cd transport from the root to the shoot in these plants, and that most of the shoot Cd resulted from uptake into the stele of the root via the symplastic pathway.
Key words: Apoplastic bypass, cadmium, durum wheat, low-abundance isotope, PTS, transpiration
Received 15 January 2007; Revised 30 April 2007 Accepted 1 May 2007