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JXB Advance Access published online on February 16, 2008
Journal of Experimental Botany, doi:10.1093/jxb/erm330
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© The Author [2008]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

RESEARCH PAPER

The high affinity K+ transporter AtHAK5 plays a physiological role in planta at very low K+ concentrations and provides a caesium uptake pathway in Arabidopsis

Zhi Qi1, Corrina R. Hampton2, Ryoung Shin1, Bronwyn J. Barkla3, Philip J. White4 and Daniel P. Schachtman1,*

1Donald Danforth Plant Science Center, 975 N. Warson Road, St Louis, MO 63132, USA
2Warwick HRI, Warwick CV35 9EF, UK
3Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, México
4Scottish Crop Research Institute, Dundee DD2 5DA, UK

* To whom correspondence should be addressed. E-mail: dschachtman{at}danforthcenter.org

Caesium (Cs+) is a potentially toxic mineral element that is released into the environment and taken up by plants. Although Cs+ is chemically similar to potassium (K+), and much is known about K+ transport mechanisms, it is not clear through which K+ transport mechanisms Cs+ is taken up by plant roots. In this study, the role of AtHAK5 in high affinity K+ and Cs+ uptake was characterized. It is demonstrated that AtHAK5 is localized to the plasma membrane under conditions of K+ deprivation, when it is expressed. Growth analysis showed that AtHAK5 plays a role during severe K+ deprivation. Under K+-deficient conditions in the presence of Cs+, Arabidopsis seedlings lacking AtHAK5 had increased inhibition of root growth and lower Cs+ accumulation, and significantly higher leaf chlorophyll concentrations than wild type. These data indicate that, in addition to transporting K+ in planta, AtHAK5 also transports Cs+. Further experiments showed that AtHAK5 mediated Cs+ uptake into yeast cells and that, although the K+ deficiency-induced expression of AtHAK5 was inhibited by low concentrations of NHFormula in planta, Cs+ uptake by yeast was stimulated by low concentrations of NHFormula. Interestingly, the growth of the Arabidopsis atakt1-1 mutant was more sensitive to Cs+ than the wild type. This may be explained, in part, by increased expression of AtHAK5 in the atakt1-1 mutant. It is concluded that AtHAK5 is a root plasma membrane uptake mechanism for K+ and Cs+ under conditions of low K+ availability.

Key words: Caesium, plasma membrane, potassium, uptake

Received 12 October 2007; Revised 27 November 2007 Accepted 28 November 2007


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