High-affinity Potassium and Sodium Transport Systems in Plants

J Exp Bot. 2006;57(5):1149-60. doi: 10.1093/jxb/erj068. Epub 2006 Jan 31.


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.

Publication types

  • Review

MeSH terms

  • Adenosine Triphosphatases / metabolism
  • Arabidopsis / genetics
  • Arabidopsis / metabolism
  • Ion Transport
  • Models, Biological
  • Plant Proteins / classification
  • Plant Proteins / genetics
  • Plant Proteins / physiology
  • Plants / genetics
  • Plants / metabolism*
  • Potassium / metabolism*
  • Potassium Channels / classification
  • Potassium Channels / genetics
  • Potassium Channels / physiology
  • Sodium / metabolism*
  • Sodium Channels / classification
  • Sodium Channels / genetics
  • Sodium Channels / physiology


  • Plant Proteins
  • Potassium Channels
  • Sodium Channels
  • Sodium
  • Adenosine Triphosphatases
  • Potassium