title: Enhancement of Na(+) uptake currents, time-dependent inward-rectifying K(+) channel currents, and K(+) channel transcripts by K(+) starvation in wheat root cells.
abstract: Excessive low-affinity Na(+) uptake is toxic to the growth of glycophytic plants. Recently, several reports have suggested that the interaction between K(+) and Na(+) uptake might represent a key factor in determining the Na(+) tolerance of plants. We investigated the effects of K(+) starvation on Na(+) and K(+) uptake mechanisms in the plasma membrane of wheat (Triticum aestivum L.) root cortex cells using the patch-clamp technique. Unexpectedly, K(+) starvation of wheat seedlings was found to enhance the magnitude and frequency of occurrence of time-dependent inward-rectifying K(+) channel currents (I(K)(+)(in)). We examined whether the transcription of a wheat root K(+)(in) channel gene is induced by K(+) starvation. A cDNA coding for a wheat root K(+) channel homolog, TaAKT1 (accession no. AF207745), was isolated. TaAKT1 mRNA levels were up-regulated in roots in response to withdrawal of K(+) from the growth medium. Furthermore, K(+) starvation caused an enhancement of instantaneous Na(+) currents (I(Na)(+)). Electrophysiological analyses suggested that I(K)(+)(in) and I(Na)(+) are not mediated by the same transport protein based on: (a) different activation curves, (b) different time dependencies, (c) different sensitivities to external Ca(2+), and (d) different cation selectivities. These data implicate a role for I(Na)(+) in Na(+) uptake and stress during K(+) starvation, and indicate that K(+)(in) channels may contribute to K(+)-starvation-induced K(+) uptake in wheat roots.
authors.affiliation: Department of Biology and Center for Molecular Genetics, University of California at San Diego, La Jolla, California 92093-0116, USA.
authors.forename: P H
authors.initials: PH
authors.lastname: Buschmann
authors.forename: R
authors.initials: R
authors.lastname: Vaidyanathan
authors.forename: W
authors.initials: W
authors.lastname: Gassmann
authors.forename: J I
authors.initials: JI
authors.lastname: Schroeder
mesh_terms: D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000166:cytology / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D014908:Triticum / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D029681:Arabidopsis Proteins; D017931:DNA Primers; D010940:Plant Proteins; D015221:Potassium Channels; D012333:RNA, Messenger; C074500:AKT1 protein, Arabidopsis; D012964:Sodium; D011188:Potassium