JXB Advance Access originally published online on January 31, 2006
Journal of Experimental Botany 2006 57(5):1149-1160; doi:10.1093/jxb/erj068
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RESEARCH PAPER |
High-affinity potassium and sodium transport systems in plants
1Laboratorio de Microbiología, Departamento de Biotecnología, Escuela Técnica Superíor de Ingenieros Agrónomos, Universidad Politécnica de Madrid, E-28040 Madrid, Spain
2Departamento de Nutrición Vegetal, Centro de Edafología y Biología Aplicada del Segura-CSIC, E-30100 Murcia, Spain
* To whom correspondence should be addressed. E-mail: alonso.rodriguez{at}upm.es
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.
Key words: Potassium transport, sodium transport
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