Sodium transport and HKT transporters: the rice model

Plant J. 2003 Jun;34(6):788-801. doi: 10.1046/j.1365-313x.2003.01764.x.

Abstract

Na+ uptake in the roots of K+-starved seedlings of barley, rice, and wheat was found to exhibit fast rate, low Km, and high sensitivity to K+. Sunflower plants responded in a similar manner but the uptake was not K+ sensitive. Ba2+ inhibited Na+ uptake, but not K+ uptake in rice roots. This demonstrated that Na+ and K+ uptake are mediated by different transporters, and that K+ blocked but was not transported by the Na+ transporter. The genome of rice cv. Nipponbare contains seven HKT genes, which may encode Na+ transporters, plus two HKT pseudogenes. Yeast expressions of OsHKT1 and OsHKT4 proved that they are Na+ transporters of high and low affinity, respectively, which are sensitive to K+ and Ba2+. Parallel experiments of K+ and Na+ uptake in yeast expressing the wheat or rice HKT1 transporters proved that they were very different; TaHKT1 transported K+ and Na+, and OsHKT1 only Na+. Transcript expressions in shoots of the OsHKT genes were fairly constant and insensitive to changes in the K+ and Na+ concentrations of the nutrient solution. In roots, the expressions were much lower than in shoots, except for OsHKT4 and OsHKT1 in K+-starved plants. We propose that OsHKT transporters are involved in Na+ movements in rice, and that OsHKT1 specifically mediates Na+ uptake in rice roots when the plants are K+ deficient. The incidence of HKT ESTs in several plant species suggests that the rice model with many HKT genes applies to other plants.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Cation Transport Proteins / chemistry
  • Cation Transport Proteins / genetics
  • Cation Transport Proteins / metabolism*
  • Conserved Sequence
  • Expressed Sequence Tags
  • Gene Expression Regulation, Plant
  • Genes, Plant
  • Ion Transport
  • Molecular Sequence Data
  • Oryza / genetics
  • Oryza / metabolism*
  • Plant Roots / genetics
  • Plant Roots / metabolism
  • Potassium / metabolism
  • Saccharomyces cerevisiae / genetics
  • Sequence Alignment
  • Sodium / metabolism*

Substances

  • Cation Transport Proteins
  • Sodium
  • Potassium

Associated data

  • GENBANK/AJ491018
  • GENBANK/AJ491815
  • GENBANK/AJ491816
  • GENBANK/AJ491817
  • GENBANK/AJ491819
  • GENBANK/AJ491820
  • GENBANK/AJ491852
  • GENBANK/AJ491853
  • GENBANK/AJ491854
  • GENBANK/AJ491855
  • GENBANK/AJ506745