title: Cell type-specific regulation of ion channels within the maize stomatal complex.
abstract: The stomatal complex of Zea mays is composed of two pore-forming guard cells and two adjacent subsidiary cells. For stomatal movement, potassium ions and anions are thought to shuttle between these two cell types. As potential cation transport pathways, K(+)-selective channels have already been identified and characterized in subsidiary cells and guard cells. However, so far the nature and regulation of anion channels in these cell types have remained unclear. In order to bridge this gap, we performed patch-clamp experiments with subsidiary cell and guard cell protoplasts. Voltage-independent anion channels were identified in both cell types which, surprisingly, exhibited different, cell-type specific dependencies on cytosolic Ca(2+) and pH. After impaling subsidiary cells of intact maize plants with microelectrodes and loading with BCECF [(2',7'-bis-(2-carboxyethyl)-5(and6)carboxyflurescein] as a fluorescent pH indicator, the regulation of ion channels by the cytosolic pH and the membrane voltage was further examined. Stomatal closure was found to be accompanied by an initial hyperpolarization and cytosolic acidification of subsidiary cells, while opposite responses were observed during stomatal opening. Our findings suggest that specific changes in membrane potential and cytosolic pH are likely to play a role in determining the direction and capacity of ion transport in subsidiary cells.
authors.affiliation: University of Würzburg, Department of Molecular Plant Physiology and Biophysics, Julius-von-Sachs-Institute, Julius-von-Sachs-Platz 2, D-97082 Würzburg, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Mumm
authors.forename: Thomas
authors.initials: T
authors.lastname: Wolf
authors.forename: Jörg
authors.initials: J
authors.lastname: Fromm
authors.forename: M Rob G
authors.initials: MR
authors.lastname: Roelfsema
authors.forename: Irene
authors.initials: I
authors.lastname: Marten
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D000838:Anions; D002118:Calcium / Q000494:pharmacology; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007473:Ion Channels / Q000378:metabolism*; D008027:Light; D008564:Membrane Potentials / Q000187:drug effects / Q000528:radiation effects; D009928:Organ Specificity / Q000187:drug effects; D010940:Plant Proteins / Q000378:metabolism*; D054046:Plant Stomata / Q000166:cytology* / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D011523:Protoplasts / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D003313:Zea mays / Q000166:cytology* / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D000838:Anions; D007473:Ion Channels; D010940:Plant Proteins; D000040:Abscisic Acid; D002118:Calcium