Ca2+Channels at the Plasma Membrane of Stomatal Guard Cells are Activated by Hyperpolarization and Abscisic Acid

• Published in: Proceedings of the National Academy of Sciences - PNAS 2000-04, Vol.97 (9), p.4967-4972
• Main Authors: David W. A. Hamilton, Hills, Adrian, Kohler, Barbara, Blatt, Michael R.
• Format: Article
• Language: English
• Subjects: Abscisic Acid - pharmacology; Acids; Biological Sciences; Biology; Calcium; Calcium Channels - drug effects; Calcium Channels - physiology; Cell Membrane - physiology; Cell membranes; Cells; Electric current; Electric potential; Fabaceae - cytology; Fabaceae - physiology; Flowers & plants; Guard cells; In Vitro Techniques; Ion Channel Gating - physiology; Ions; Membrane Potentials; P branes; Patch-Clamp Techniques; Pipettes; Plant cells; Plants, Medicinal; Potassium; Protoplasts; Protoplasts - physiology; Solutes
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.080068897

In stomatal guard cells of higher-plant leaves, abscisic acid (ABA) evokes increases in cytosolic free Ca2+concentration ([Ca2+]i) by means of Ca2+entry from outside and release from intracellular stores. The mechanism(s) for Ca2+flux across the plasma membrane is poorly understood. Because [Ca2+]iincreases are voltage-sensitive, we suspected a Ca2+channel at the guard cell plasma membrane that activates on hyperpolarization and is regulated by ABA. We recorded single-channel currents across the Vicia guard cell plasma membrane using Ba2+as a charge-carrying ion. Both cell-attached and excised-patch measurements uncovered single-channel events with a maximum conductance of 12.8 ± 0.4 pS and a high selectivity for Ba2+(and Ca2+) over K+and Cl-. Unlike other Ca2+channels characterized to date, these channels rectified strongly toward negative voltages with an open probability (Po) that increased with [Ba2+] outside and decreased roughly 10-fold when [Ca2+]iwas raised from 200 nM to 2 μ M. Adding 20 μ M ABA increased Po, initially by 63- to 260-fold; in both cell-attached and excised patches, it shifted the voltage sensitivity for channel activation, and evoked damped oscillations in Powith periods near 50 s. A similar, but delayed response was observed in 0.1 μ M ABA. These results identify a Ca2+-selective channel that can account for Ca2+influx and increases in [Ca2+]itriggered by voltage and ABA, and they imply a close physical coupling at the plasma membrane between ABA perception and Ca2+channel control.