JXB Advance Access first published online on January 31, 2006
This version published online on February 23, 2006
Journal of Experimental Botany, doi:10.1093/jxb/erj068
1 Laboratorio de Microbiología, Departamento de Biotecnología, Escuela Técnica Superíor de Ingenieros Agrónomos, Universidad Politécnica de Madrid, E-28040 Madrid, Spain
* To whom correspondence should be addressed. All living cells have an absolute requirement for K+, which must be taken up from the external medium. In contrast to marine organisms, which live in a medium with an inexhaustible supply of K+, terrestrial life evolved in oligotrophic environments where the low supply of K+ limited the growth of colonizing plants. In these limiting conditions Na+ could substitute for K+ in some cellular functions, but in others it is toxic. In the vacuole, Na+ is not toxic and can undertake osmotic functions, reducing the total K+ requirements and improving growth when the lack of K+ is a limiting factor. Because of these physiological requirements, the terrestrial life of plants depends on high-affinity K+ uptake systems and benefits from high-affinity Na+ uptake systems. In plants, both systems have received extensive attention during recent years and a clear insight of their functions is emerging. Some plant HAK transporters mediate high-affinity K+ uptake in yeast, mimicking K+ uptake in roots, while other members of the same family may be K+ transporters in the tonoplast. In parallel with the HAK transporters, some HKT transporters mediate high-affinity Na+ uptake without cotransporting K+. HKT transporters have two functions: (i) to take up Na+ from the soil solution to reduce K+ requirements when K+ is a limiting factor, and (ii) to reduce Na+ accumulation in leaves by both removing Na+ from the xylem sap and loading Na+ into the phloem sap. This is a new version of this article as there was an error in one of the references in the first version.
Received May 27, 2005
Accepted September 12, 2005
SALINITY SPECIAL ISSUE ARTICLE
High-affinity potassium and sodium transport systems in plants
Alonso Rodríguez-Navarro 1 *
and
Francisco Rubio 2
2 Departamento de Nutrición Vegetal, Centro de Edafología y Biología Aplicada del Segura-CSIC, E-30100 Murcia, Spain
Alonso Rodríguez-Navarro, E-mail: alonso.rodriguez{at}upm.es
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