Plant and Cell Physiology Advance Access originally published online on August 4, 2005
Plant and Cell Physiology 2005 46(10):1682-1689; doi:10.1093/pcp/pci184
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Nucleotides and Mg2+ Ions Differentially Regulate K+ Channels and Non-Selective Cation Channels Present in Cells Forming the Stomatal Complex
Molecular Plant Physiology and Biophysics, Julius-von-Sachs Institute for Bioscience, University of Wuerzburg, Julius-von-Sachs-Platz 2, D-97082 Wuerzburg, Germany
* Corresponding author: E-mail, marten{at}botanik.uni-wuerzburg.de; Fax, +49-931-8886158.
Voltage-dependent inward-rectifying (Kin) and outward-rectifying (Kout) K+ channels are capable of mediating K+ fluxes across the plasma membrane. Previous studies on guard cells or heterologously expressed K+ channels provided evidence for the requirement of ATP to maintain K+ channel activity. Here, the nucleotide and Mg2+ dependencies of time-dependent Kin and Kout channels from maize subsidiary cells were examined, showing that MgATP as well as MgADP function as channel activators. In addition to Kout channels, these studies revealed the presence of another outward-rectifying channel type (MgC) in the plasma membrane that however gates in a nucleotide-independent manner. MgC represents a new channel type distinguished from Kout channels by fast activation kinetics, inhibition by elevated intracellular Mg2+ concentration, permeability for K+ as well as for Na+ and insensitivity towards TEA+. Similar observations made for guard cells from Zea mays and Vicia faba suggest a conserved regulation of channel-mediated K+ and Na+ transport in both cell types and species.
1 Present address: Molecular Plant Physiology, University of Erlangen-Nuernberg, D-91058 Erlangen, Germany
(Received May 24, 2005; Accepted July 31, 2005)
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