Abstract
Stomatal movements depend on an osmoregulation process in which swelling or shrinking of the guard cells opens or closes the stomatal pore. Ions and water fluxes are an essential aspect of guard cell osmoregulation. Thus far, studies of these fluxes have focused on the guard cell plasma membrane. Guard cells, however, are a multi-compartment system that includes a prominent vacuole, which has a primary role in turgor regulation. This study reports on a detailed characterization of an ion channel at the guard cell tonoplast of Allium cepa (onion). We used patch-clamp methodology with isolated tonoplast patches to study conduction and gating at the single channel level. A voltage-dependent outward-rectifying cationic channel (210 picosiemens) was the dominant conductance. In symmetrical solutions the channel displayed an ohmic behavior in its current-voltage relationship. It also showed a very large rectification in the open probability. The channel was predominantly cationic and its sequence of ionic selectivity was weak (Na+ > K+ > Rb+ > Cs+). The channel conductance was not affected by intravacuolar pH. Analysis of membrane patches with multiple channels showed that the probability of a channel to open was independent of the opening of the other channels present in the patch and that there was a conservation of the open probability for different channels. Ensemble records generated using a pulse protocol showed slow activation and deactivation kinetics. A first-latency analysis of single-channel records in response to protocols with different prepulse duration indicated that this channel has more than one closed state.
Full Text
The Full Text of this article is available as a PDF (740.2 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Aldrich R. W., Corey D. P., Stevens C. F. A reinterpretation of mammalian sodium channel gating based on single channel recording. Nature. 1983 Dec 1;306(5942):436–441. doi: 10.1038/306436a0. [DOI] [PubMed] [Google Scholar]
- Cosgrove D. J., Hedrich R. Stretch-activated chloride, potassium, and calcium channels coexisting in plasma membranes of guard cells of Vicia faba L. Planta. 1991 Dec;186(1):143–153. doi: 10.1007/BF00201510. [DOI] [PubMed] [Google Scholar]
- Davies J. M., Poole R. J., Rea P. A., Sanders D. Potassium transport into plant vacuoles energized directly by a proton-pumping inorganic pyrophosphatase. Proc Natl Acad Sci U S A. 1992 Dec 15;89(24):11701–11705. doi: 10.1073/pnas.89.24.11701. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Fenwick E. M., Marty A., Neher E. Sodium and calcium channels in bovine chromaffin cells. J Physiol. 1982 Oct;331:599–635. doi: 10.1113/jphysiol.1982.sp014394. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Gambale F., Cantu A. M., Carpaneto A., Keller B. U. Fast and slow activation of voltage-dependent ion channels in radish vacuoles. Biophys J. 1993 Nov;65(5):1837–1843. doi: 10.1016/S0006-3495(93)81241-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Gilroy S., Fricker M. D., Read N. D., Trewavas A. J. Role of Calcium in Signal Transduction of Commelina Guard Cells. Plant Cell. 1991 Apr;3(4):333–344. doi: 10.1105/tpc.3.4.333. [DOI] [PMC free article] [PubMed] [Google Scholar]
- HODGKIN A. L., KATZ B. The effect of sodium ions on the electrical activity of giant axon of the squid. J Physiol. 1949 Mar 1;108(1):37–77. doi: 10.1113/jphysiol.1949.sp004310. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hedrich R., Busch H., Raschke K. Ca2+ and nucleotide dependent regulation of voltage dependent anion channels in the plasma membrane of guard cells. EMBO J. 1990 Dec;9(12):3889–3892. doi: 10.1002/j.1460-2075.1990.tb07608.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Horn R., Patlak J., Stevens C. F. Sodium channels need not open before they inactivate. Nature. 1981 Jun 4;291(5814):426–427. doi: 10.1038/291426a0. [DOI] [PubMed] [Google Scholar]
- Marten I., Zeilinger C., Redhead C., Landry D. W., al-Awqati Q., Hedrich R. Identification and modulation of a voltage-dependent anion channel in the plasma membrane of guard cells by high-affinity ligands. EMBO J. 1992 Oct;11(10):3569–3575. doi: 10.1002/j.1460-2075.1992.tb05440.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Neher E. Correction for liquid junction potentials in patch clamp experiments. Methods Enzymol. 1992;207:123–131. doi: 10.1016/0076-6879(92)07008-c. [DOI] [PubMed] [Google Scholar]
- Pantoja O., Gelli A., Blumwald E. Characterization of Vacuolar Malate and K Channels under Physiological Conditions. Plant Physiol. 1992 Nov;100(3):1137–1141. doi: 10.1104/pp.100.3.1137. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Schnabl H., Raschke K. Potassium Chloride as Stomatal Osmoticum in Allium cepa L., a Species Devoid of Starch in Guard Cells. Plant Physiol. 1980 Jan;65(1):88–93. doi: 10.1104/pp.65.1.88. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Schwartz A. Role of Ca and EGTA on Stomatal Movements in Commelina communis L. Plant Physiol. 1985 Dec;79(4):1003–1005. doi: 10.1104/pp.79.4.1003. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Serrano E. E., Zeiger E. Sensory transduction and electrical signaling in guard cells. Plant Physiol. 1989 Nov;91(3):795–799. doi: 10.1104/pp.91.3.795. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Zeiger E., Hepler P. K. Blue light-induced, intrinsic vacuolar fluorescence in onion guard cells. J Cell Sci. 1979 Jun;37:1–10. doi: 10.1242/jcs.37.1.1. [DOI] [PubMed] [Google Scholar]
- Zeiger E., Hepler P. K. Production of guard cell protoplasts from onion and tobacco. Plant Physiol. 1976 Oct;58(4):492–498. doi: 10.1104/pp.58.4.492. [DOI] [PMC free article] [PubMed] [Google Scholar]