JXB Advance Access originally published online on November 1, 2006
Journal of Experimental Botany 2006 57(15):4111-4122; doi:10.1093/jxb/erl184
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RESEARCH PAPER |
Root-to-shoot long-distance circulation of nicotianamine and nicotianaminenickel chelates in the metal hyperaccumulator Thlaspi caerulescens
1Biochimie et Physiologie Moléculaire des Plantes, Centre National de la Recherche Scientifique (UMR 5004), Institut National de la Recherche Agronomique, Université Montpellier 2, École Nationale Supérieure d'Agronomie, 2 Place Viala, F-34060 Montpellier cedex 2, France
2Laboratoire de Chimie Bio-Inorganique Environnement, Centre National de la Recherche Scientifique (UMR 5034) Hélioparc, 2 avenue du Professeur Angot, F-64053 Pau cedex 09, France
* To whom correspondence should be addressed. E-mail: czernic{at}univ-montp2.fr
Plant metal hyperaccumulator species are widely used as models to unravel the heavy metal tolerance and hyperaccumulation mechanisms. Thlaspi caerulescens is capable of tolerating and hyperaccumulating Zn, Cd, and Ni. A search for factors involved in the cellular tolerance to Ni, based on yeast screens, led to isolation of a cDNA encoding a functional nicotianamine (NA) synthase (NAS). The T. caerulescens genome appears to contain a single copy of the NAS gene named TcNAS whose expression is restricted to the leaves. The analysis of doseresponse and time-course Ni treatments have revealed that the exposure to Ni triggers the accumulation of NA in the roots. Because neither TcNAS expression nor NAS activity were detected in the roots, the NA accumulation in roots is most probably the result of its translocation from the leaves. Once in the roots, NA, together with Ni, is subsequently found in the xylem, for redirection to the aerial parts. Using liquid chromatography coupled to inductively coupled plasma or electrospray ionization mass spectrometry, it has been shown that part of the Ni is translocated as a stable NiNA complex in the xylem sap. This circulation of NA, Ni, and NANi chelates is absent in the non-tolerant non-hyperaccumulator related species T. arvense. Taken together, the results provide direct physiological and chemical evidence for NA and NAheavy metal complex translocation in a hyperaccumulator species.
Key words: Circulation, metal chelation, metal hyperaccumulation, nicotianamine, nickel
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