Electrical Potentials in Stomatal Complexes

Saftner, Robert A.; Raschke, Klaus

doi:10.1104/pp.67.6.1124

Cited by 39 publications

(23 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1 and 2 were in the range of the physiologically expected free K+ concentrations in the cell wall and the cytoplasm (2). The resting potential of nonstimulated guard cells has been postulated to be Nernstian with respect to K+ (27). The voltage sensitivity of K+ channels as described here implies that K+ fluxes into and out of guard cells may be regulated by mechanisms that produce changes in the membrane potential.…”

Section: Resultsmentioning

confidence: 77%

Voltage dependence of K ⁺ channels in guard-cell protoplasts

Schroeder

Raschke

Neher

1987

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

405

363

View full text Add to dashboard Cite

Stomatal pores in leaves enable plants to regulate the exchange of gases with their environment. Variations of the pore aperture are mediated by controlled changes of potassium salt concentrations in the surrounding guard cells. The voltage-dependent gating of K+-selective channels in the plasma membrane (plasmalemma) of cell-wall-free guard cells (protoplasts) was studied at the molecular level in order to investigate the regulation of K+ fluxes during stomatal movements. Inward and outward K+ currents across the plasmalemma of guard cells were identified by using the whole-cell configuration of the patch-clamp technique. Depolarizations of the membrane potential from a holding potential of -60 mV to values more positive than -40 mV produced outward currents that were shown to be carried by KV. Hyperpolarizations elicited inward K+ currents. Inward and outward currents were selective for K+ over Na' and could be partially blocked by exposure to extracellular Ba2 . In cell-attached and excised membrane patches, previously identified KV-selective single channels in guard cells were studied. Averaging of singlechannel currents during voltage pulses resulted in activation and deactivation kinetics that were similar to corresponding kinetics of inward and outward currents in whole cells, showing that K+-selective channels were the molecular pathways for the K+ currents recorded across the plasmalemma of single guardcell protoplasts. Estimates demonstrate that K+ currents through the voltage-gated K+ channels recorded in whole guard cells can account for physiological K+ fluxes reported to occur during stomatal movements in leaves.Elucidation of the molecular mechanisms involved in the transport of K+ across membranes of higher plant cells is fundamental to the understanding of osmoregulation and cell-volume control. Our studies have focused on the specialized guard cells surrounding stomatal pores in the lower epidermis of leaves of Viciafaba. Two guard cells modulate the aperture ofthe pore they surround, allowing the exchange of CO2 and 02 for photosynthesis, while minimizing water loss to the atmosphere. Light, among other physiological factors, causes guard cells to accumulate K+, leading to the opening of the pore (for reviews, see refs. 1-3). Darkening, high CO2 concentrations, and the phytohormone abscisic acid (under a condition of drought) mediate pore closure by inducing the release of K+ and counter ions (4, 5). Recently, ion channels have been identified in the plasmalemma of guard cells that are selectively permeable to K+ and through which K+ can be accumulated and released (6). In the present study, we have investigated the voltage-dependent activation of K+-selective channels in guard-cell protoplasts to explore possible mechanisms involved in the regulation of stomatal apertures. METHODSGuard-Cell Protoplasts. These were isolated from the lower epidermis of leaves from 2-to 3-week-old Vicia faba plants by 30-to 40-min incubation in 0.3 M D-mannitol/1 mM CaCl2/2% cellulase Onozuka RS (Yakult ...

show abstract

Section: Resultsmentioning

confidence: 77%

Voltage dependence of K ⁺ channels in guard-cell protoplasts

Schroeder

Raschke

Neher

1987

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

405

363

View full text Add to dashboard Cite

show abstract

“…The fact that previous attempts failed to elicit electrical responses to cyanide from guard cells (Saftner & Raschke, 1981) can be ascribed now to the deleterious effects of microelectrode salt leakage (Blatt, 1987a). Figure 2 shows the records from four cells exposed to 0.3 and 1.0 mM NaCN plus 0.4 mM SHAM (see also Table 1).…”

Section: Atp Cyanide and Guard Cell Potentialsmentioning

confidence: 95%

Electrical characteristics of stomatal guard cells: The contribution of ATP-dependent, “Electrogenic” transport revealed by current-voltage and difference-current-voltage analysis

Blatt

1987

J. Membrain Biol.

View full text Add to dashboard Cite

Summary. The steady-state, current-voltage (I-V) characteristicsof stomatal guard cells from Vicia faba L. were explored by voltage clamp using conventional electrophysiological techniques, but with double-barrelled microelectrodes containing 50 mM K+-acetate. Attention was focused, primarily, on guard cell response to metabolic blockade. Exposures to 0.3-1.0 mM NaCN and 0.4 mM salicylhydroxamic acid (SHAM) lead consistently to depolarizing (positive-going) shifts in guard cell potentials (V~), as large as + 103 mV, which were generally complete within 60-90 sec (mean response half-time, 10.3 -+ 1.7 sec); values for V~ in NaCN plus SHAM were close or positive to -100 mV and well removed from the K + equilibrium potential. Guard cell ATP content, which was followed in parallel experiments, showed a mean half-time for decay of 1().8 + 1.9 sec ([ATP]t~0, 1.32 -+ 0.28 mM; lATP],=60-fs0 .... 0.29 -+ 0.40 mM). In respiring cells, the I-V relations were commonly sigmoid about V,, or gently concave to the voltage axis positive to V~. Inward-and outward-rectifying currents were also observed, especially near the voltage extremes (nominally -350 and +50 mV). Short-circuit currents (at V = 0 mV) were typically about 200-500 mAm -2. The principal effect of cyanide early on was to linearize the I-V characteristic while shifting it to the right along the voltage axis, to decrease the membrane conductance, and to reduce the short-circuit current by approx. 50-75%. The resulting difference-current-voltage (dl-V) curves (+cyanide) showed a marked sensitivity to voltages negative from -100 mV and, when clamp scans had been extended sufficiently, they revealed a distinct minimum near -300 mV before rising at still more negative potentials. The difference currents, along with changes in guard cell potential, conductance and ATP content are interpreted in context of a primary, ATPconsuming ion pump. Fitting dl-V curves to reaction kinetic model for the pump J. Membrane Biol. 63:165; Blatt, M.R. (1986)J. Membrane Biol. 92:91] implicates a stoichiometry of one (+) charge transported outward for each ATP hydrolyzed, with pump currents as high as 200 mA m 2 at the free-running potential. The analysis indicates that the pump can comprise more than half of the total membrane conductance and argues against modulations of pump activity alone, as an effective means to controlling K + transport for stomatal movements. Key Wordsstomatal guard cell -(difference-) current-voltage relation 9 conductance-voltage relation 9 H + pump . kinetic carrier model 9 K + transport -Vicia

show abstract

“…The positive potential may be caused by membrane damage during enzymatic treatment (Cornel et al 1983). Furthermore, potential value may also change depending on the concentration of outer ions (Saftner andRaschke 1981, Abe andTakeda 1986) and suction pressure (Pantoja and Willmer 1986).…”

Section: Vacuolar Ph Measurement Of Colored Cells Of Hydrangeamentioning

confidence: 99%

Sepal Color Variation of Hydrangea macrophylla and Vacuolar pH Measured with a Proton-Selective Microelectrode

Yoshida

Toyama-Kato

Kameda

et al. 2003

Plant and Cell Physiology

122

101

View full text Add to dashboard Cite

;Sepal color of hydrangea varies with the environmental conditions. Although chemical and biological studies on this color variation have a long history, little correct knowledge has been generated about color development. All colored sepals contain the same anthocyanin, delphinidin 3-glucoside. Thus, there must be some other system for developing the wide variety of colors. In hydrangea sepals the cells of the epidermis are colorless and only the second layer of cells contain pigment. We prepared protoplasts without any color change during enzyme treatment of sepals and measured the vacuolar pH of each of the colored cells. We could correlate the color of a single hydrangea cell with its vacuolar pH using a combination of micro-spectrophotometry and a proton-selective microelectrode. Values for the vacuolar pH of blue (lvismax: 589 nm) and red cells (lvismax: 537 nm) were 4.1 and 3.3, respectively, the vacuolar pH of blue cells being significantly higher.

show abstract

Electrical Potentials in Stomatal Complexes

Cited by 39 publications

References 13 publications

Voltage dependence of K ⁺ channels in guard-cell protoplasts

Voltage dependence of K ⁺ channels in guard-cell protoplasts

Electrical characteristics of stomatal guard cells: The contribution of ATP-dependent, “Electrogenic” transport revealed by current-voltage and difference-current-voltage analysis

Sepal Color Variation of Hydrangea macrophylla and Vacuolar pH Measured with a Proton-Selective Microelectrode

Contact Info

Product

Resources

About

Electrical Potentials in Stomatal Complexes

Cited by 39 publications

References 13 publications

Voltage dependence of K + channels in guard-cell protoplasts

Voltage dependence of K + channels in guard-cell protoplasts

Electrical characteristics of stomatal guard cells: The contribution of ATP-dependent, “Electrogenic” transport revealed by current-voltage and difference-current-voltage analysis

Sepal Color Variation of Hydrangea macrophylla and Vacuolar pH Measured with a Proton-Selective Microelectrode

Contact Info

Product

Resources

About

Voltage dependence of K ⁺ channels in guard-cell protoplasts

Voltage dependence of K ⁺ channels in guard-cell protoplasts