Journal Article

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

Zhi Qi, Corrina R. Hampton, Ryoung Shin, Bronwyn J. Barkla, Philip J. White and Daniel P. Schachtman

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 59, issue 3, pages 595-607
Published in print February 2008 | ISSN: 0022-0957
Published online February 2008 | e-ISSN: 1460-2431 | DOI: http://dx.doi.org/10.1093/jxb/erm330
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

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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 NH4+ in planta, Cs+ uptake by yeast was stimulated by low concentrations of NH4+. 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.

Keywords: Caesium; plasma membrane; potassium; uptake

Journal Article.  8012 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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