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  • The EMBO Journal (2003) 22, 2004 - 2014
  • doi:10.1093/emboj/cdg207

Functional analysis of AtHKT1 in Arabidopsis shows that Na+ recirculation by the phloem is crucial for salt tolerance

Pierre Berthomieu1, Geneviève Conéjéro1, Aurélie Nublat1, William J. Brackenbury1, Cécile Lambert1, Cristina Savio1, Nobuyuki Uozumi2, Shigetoshi Oiki3, Katsuyuki Yamada3, Françoise Cellier1, Françoise Gosti1, Thierry Simonneau4, Pauline A. Essah5, Mark Tester5, Anne-Aliénor Véry1, Hervé Sentenac1 and Francine Casse1

  1. Biochimie et Physiologie Moléculaire des Plantes, UMR 5004, ENSA.M INRA CNRS UMII, 34060 Montpellier Cedex 2, France
  2. Bioscience Center, Nagoya University, Nagoya 464-8601, Japan
  3. Department of Physiology, Fukui Medical University, Fukui 910-1193, Japan
  4. UMR Agronomie Ecophysiologie des Plantes sous Stress Environnementaux, INRA ENSA.M, 34060 Montpellier Cedex 2, France
  5. Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK

Correspondence to:

Pierre Berthomieu, E-mail: berthom@ensam.inra.fr

Received 29 September 2002; Accepted 6 March 2003; Revised 5 March 2003

Two allelic recessive mutations of Arabidopsis, sas2-1 and sas2-2, were identified as inducing sodium overaccumulation in shoots. The sas2 locus was found (by positional cloning) to correspond to the AtHKT1 gene. Expression in Xenopus oocytes revealed that the sas2-1 mutation did not affect the ionic selectivity of the transporter but strongly reduced the macro scopic (whole oocyte current) transport activity. In Arabidopsis, expression of AtHKT1 was shown to be restricted to the phloem tissues in all organs. The sas2-1 mutation strongly decreased Na+ concentration in the phloem sap. It led to Na+ overaccumulation in every aerial organ (except the stem), but to Na+ underaccumulation in roots. The sas2 plants displayed increased sensitivity to NaCl, with reduced growth and even death under moderate salinity. The whole set of data indicates that AtHKT1 is involved in Na+ recirculation from shoots to roots, probably by mediating Na+ loading into the phloem sap in shoots and unloading in roots, this recirculation removing large amounts of Na+ from the shoot and playing a crucial role in plant tolerance to salt.

  • Keywords:

    • Na+ exclusion,
    • Na+ transport,
    • phloem,
    • positional cloning,
    • salt tolerance