First published online February 25, 2005; 10.1104/pp.104.057216
Plant Physiology 137:1105-1114 (2005)
© 2005 American Society of Plant Biologists
ENVIRONMENTAL STRESS AND ADAPTATION
The Potassium Transporter AtHAK5 Functions in K+ Deprivation-Induced High-Affinity K+ Uptake and AKT1 K+ Channel Contribution to K+ Uptake Kinetics in Arabidopsis Roots1,[w]
Markus Gierth2,
Pascal Mäser3 and
Julian I. Schroeder*
Division of Biological Sciences, Cell and Developmental Biology Section and Center for Molecular Genetics, University of California San Diego, La Jolla, California 92093–0116
Potassium is an important macronutrient and the most abundant cation in plants. Because soil mineral conditions can vary, plants must be able to adjust to different nutrient availabilities. Here, we used Affymetrix Genechip microarrays to identify genes responsive to potassium (K+) deprivation in roots of mature Arabidopsis (Arabidopsis thaliana) plants. Unexpectedly, only a few genes were changed in their expression level after 6, 48, and 96 h of K+ starvation even though root K+ content was reduced by approximately 60%. AtHAK5, a potassium transporter gene from the KUP/HAK/KT family, was most consistently and strongly up-regulated in its expression level across 48-h, 96-h, and 7-d K+ deprivation experiments. AtHAK5 promoter- -glucuronidase and -green fluorescent protein fusions showed AtHAK5 promoter activity in the epidermis and vasculature of K+ deprived roots. Rb+ uptake kinetics in roots of athak5 T-DNA insertion mutants and wild-type plants demonstrated the absence of a major part of an inducible high-affinity Rb+/K+ (Km approximately 15–24 µM) transport system in athak5 plants. In comparative analyses, uptake kinetics of the K+ channel mutant akt1-1 showed that akt1-1 roots are mainly impaired in a major transport mechanism, with an apparent affinity of approximately 0.9 mM K+(Rb+). Data show adaptation of apparent K+ affinities of Arabidopsis roots when individual K+ transporter genes are disrupted. In addition, the limited transcriptome-wide response to K+ starvation indicates that posttranscriptional mechanisms may play important roles in root adaptation to K+ availability in Arabidopsis. The results demonstrate an in vivo function for AtHAK5 in the inducible high-affinity K+ uptake system in Arabidopsis roots.
1 This work was supported by the Department of Energy (grant no. DE–FG02–03ER15449), by the National Science Foundation (grant no. DBI–0077378 to J.I.S.), by the Alexander von Humboldt Foundation (a Feodor-Lynen Fellowship to M.G.), and by the Human Frontier Science Program (fellowship to P.M.).
2 Present address: University of Cologne, Institute of Botany II, Gyrhofstr. 15, 50931 Köln, Germany.
3 Present address: University of Bern, Institute of Cell Biology, Baltzerstr. 4, CH–3012 Bern, Switzerland.
[w] The online version of this article contains Web-only data.
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.057216.
* Corresponding author; julian{at}biomail.ucsd.edu; fax 1–858–534–7108.
Received November 24, 2004;
returned for revision December 29, 2004;
accepted December 29, 2004.
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