A novel chloride channel in Vicia faba guard cell vacuoles activated by the serine/threonine kinase, CDPK.
Calcium-Dependent Protein Kinases (CDPKs) in higher plants contain a C-terminal calmodulin-like regulatory domain. Little is known regarding physiological CDPK targets. Both kinase activity and multiple Ca2+-dependent signaling pathways have been implicated in the control of stomatal guard cell movements. To determine whether CDPK or other protein kinases could have a role in guard cell signaling, purified and recombinant kinases were applied to Vicia faba guard cell vacuoles during patch-clamp experiments. CDPK activated novel vacuolar chloride (VCL) and malate conductances in guard cells. Activation was dependent on both Ca2+ and ATP. Furthermore, VCL activation occurred in the absence of Ca2+ using a Ca2+-independent, constitutively active, CDPK* mutant. Protein kinase A showed weaker activation (22% as compared with CDPK). Current reversals in whole vacuole recordings shifted with the Nernst potential for Cl-and vanished in glutamate. Single channel recordings showed a CDPK-activated 34 +/- 5 pS Cl- channel. VCL channels were activated at physiological potentials enabling Cl- uptake into vacuoles. VCL channels may provide a previously unidentified, but necessary, pathway for anion uptake into vacuoles required for stomatal opening. CDPK-activated VCL currents were also observed in red beet vacuoles suggesting that these channels may provide a more general mechanism for kinase-dependent anion uptake.
Pei
Z M
ZM
Department of Biology and Center for Molecular Genetics, University of California, San Diego, La Jolla 92093-0116, USA.
Ward
J M
JM
Harper
J F
JF
Schroeder
J I
JI
D000255:Adenosine Triphosphate / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002465:Cell Movement; D018118:Chloride Channels / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism; D007887:Fabaceae / Q000166:cytology* / Q000502:physiology*; D007700:Kinetics; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D010946:Plants, Medicinal; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D013045:Species Specificity; D014617:Vacuoles / Q000502:physiology / Q000648:ultrastructure; D014675:Vegetables
D018118:Chloride Channels; D000255:Adenosine Triphosphate; D017346:Protein Serine-Threonine Kinases; D002118:Calcium