Cloning and electrophysiological analysis of KST1, an inward rectifying K+ channel expressed in potato guard cells.
Potassium uptake by guard cells represents part of the osmotic motor which drives stomatal opening. Patch-clamp measurements have identified inward rectifying K+ channels capable of mediating K+ uptake in guard cells and various other plant cell types. Here we report the molecular cloning and characterization of a voltage-dependent K+ channel (KST1) from potato (Solanum tuberosum L.) guard cells. In situ hybridization shows expression of kst1 in guard cells. Two-electrode voltage-clamp and patch-clamp studies of the gene product after cRNA injection into Xenopus oocytes identified KST1 as a slowly activating, voltage-dependent, inward rectifying K+ channel. The single channel current voltage curve was linear in the range -160 to +20 mV, with a deduced single channel conductance of 7 pS in symmetrical 100 mM K+. This channel type, modulated by pH changes within the physiological range, required ATP for activation. In line with the properties of a K(+)-selective channel, KST1 was permeable to K+, Rb+ and NH4+ and excluded Na+ and Li+. Cs+ at submillimolar concentrations blocked the channel in a voltage-dependent manner. Related studies on potato guard cell protoplasts confirmed the biophysical characteristics of the kst1 gene product (KST1) in the heterologous expression system. Therefore, KST1 represents a major K+ uptake channel in potato guard cells.
Müller-Röber
B
B
Institut für Genbiologische Forschung Berlin GmbH, Germany.
Ellenberg
J
J
Provart
N
N
Willmitzer
L
L
Busch
H
H
Becker
D
D
Dietrich
P
P
Hoth
S
S
Hedrich
R
R
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002412:Cations; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D004594:Electrophysiology; D005260:Female; D015870:Gene Expression; D017343:Genes, Plant; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D010944:Plants / Q000235:genetics* / Q000378:metabolism*; D015221:Potassium Channels / Q000235:genetics* / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D011198:Solanum tuberosum / Q000235:genetics / Q000378:metabolism; D014981:Xenopus
D002412:Cations; D018076:DNA, Complementary; D018744:DNA, Plant; D015221:Potassium Channels