Ionic Channels in Plant Protoplasts

Moran, Nava; Ehrenstein, Gerald; Iwasa, Kuni H.; Bare, Charles; Mischke, Charles

doi:10.1007/978-1-4684-5077-4_12

Cited by 8 publications

(10 citation statements)

References 21 publications

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“…In spite of the fluctuation observed in both N and P0 (not shown), in the above two patches N decreased significantly from 4.4 _+ 0.3 (-SEM), by 2.0 + 0.3 (P < 0.005), while the average change in P0 was not significantly different from zero (-0.04 -+ 0.03; P < 0.30, two-sided paired t test). We have not studied systematically the fluctuations in fi to decide on a possible underlying mechanism, such as shifts between various modes of gating and cooperativity among the channels (e.g., Draber et al, 1993, Iwasa et al, 1986. The elucidation of these phenomena requires additional experiments.…”

Section: The Effect Of Ph On Single Kd Channelsmentioning

confidence: 99%

“…KH and KD channels are the most predominant K channel types in the plasma membrane of protoplasts from stomatal guard cells of Vicia faba (Hedrich and Schroeder, 1989), and, in fact, in most higher plant cells examined so far (Moran, Ehrenstein, Iwasa, Bare, and Mischke, 1986;Moran, Ehrenstein, Iwasa, Mischke, and Satter, 1988;Moran and Satter, 1989;Schauf and Wilson, 1987;Ketchum, Shrier, and Poole, 1989; see recent reviews by Tester, 1990;Blatt, 1991). The characterization of these channels in plants still lags behind their counterparts in animal cell membranes (see, for example, recent reviews by Sanders, 1990, Hille, 1992 in biophysical as well as in biochemical detail.…”

Section: Introductionmentioning

confidence: 99%

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External pH effects on the depolarization-activated K channels in guard cell protoplasts of Vicia faba.

Ilan

Schwartz

Moran

1994

The Journal of General Physiology

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Previous studies reveal that the pH of the apoplastic solution in the guard cell walls may vary between 7.2 and 5.1 in closed and open stomata, respectively. During these aperture and pH changes, massive K § fluxes cross the cellular plasma membrane driving the osmotic turgor and volume changes of guard cells. Therefore, we examined the effect of extracellular pH on the depolarizationactivated K channels (KD channels), which constitute the K § efflux pathway, in the plasma membrane of Viciafaba guard cell protuplasts. We used patch clamp, both in whole cells as well as in excised outside-out membrane patches.Approximately 500 KD channels, at least, could be activated by depolarization in one protoplast (density: ~0.6 ~m-2). Acidification from pH 8.1 to 4.4 decreased markedly the whole-cell conductance, GK, of the KD channels, shifted its voltage dependence, GK-EM, to the right on the voltage axis, slowed the rate of activation and increased the ,rate of deactivation, whereas the single channel conductance was not affected significantly. Based on the GK-EM shifts, the estimated average negative surface charge spacing near the KD channel is 39 /~. To quantify the effects of protons on the rates of transitions between the hypothesized conformational states of the channels, we fitted the experimental macroscopic steady state conductancevoltage relationship and the voltage dependence of time constants of activation and deactivation, simultaneously, with a sequential three-state model CCO. In terms of this model, protonation affects the voltage-dependent properties via a decrease in localized, rather than homogeneous, surface charge sensed by the gating moieties. In terms of either the CO or CCO model, the protonation of a site with a pKa of 4.8 decreases the voltage-independent number of channels, N, that are available for activation by depolarization.

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Section: The Effect Of Ph On Single Kd Channelsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

External pH effects on the depolarization-activated K channels in guard cell protoplasts of Vicia faba.

Ilan

Schwartz

Moran

1994

The Journal of General Physiology

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“…A TEA"'"-sensitive, PD-independent Kĉ onductance in corn cells bears further investigation (Ketchum et al, 1989). Many workers have seen channels without characterizing them in detail and presumably many of these will prove to be K+ channels (Krawczyk, 1978;Moran et al, 1984Moran et al, , 1985Moran et al, , 1986Coleman, 1986;Iijima & Hagiwara, 1987;Hosoi et al, 1988;Stoeckel & Takeda, 1989).…”

Section: Other Plasma Membrane K^ Channelsmentioning

confidence: 99%

Tansley Review No. 21 Plant ion channels: whole‐cell and single channel studies

Tester¹

1990

New Phytologist

301

166

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SUMMARY Ion channels are proteins which catalyse rapid, passive, electrogenic uniport of ions through pores spanning an otherwise poorly permeable lipid bilayer. Among other processes, fluxes through ion channels are responsible for action potentials – large, transient changes in membrane potential which have been known of in plants for over 100 years. Much disparate information on ion channels in plant cells has accumulated over the past few years. In an attempt to synthesize these data, the properties of at least 18 different ion channels are collated in this review. Channels are initially classified according to ion selectivity (Ca2+, Cl−, K+ and H+); then gating characteristics (i.e. control of opening and closing), unitary conductance and pharmacology are used to distinguish further different sub‐types of channels. To provide a background for this overview, the fundamental properties which define ion channels in animal cells, namely conduction, selectivity and gating, are described. Appropriate techniques for the study of ion channels are also assessed. The review concludes with a discussion on the role of ion channels in plant cells, although any comment on functions beyond turgor regulation and general statements about signalling remains largely speculative. The study of ion channels in plant cells is still at an early stage and it is hoped that this review will provide a framework upon which further work in both algae and vascular plants can be based.

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“…K+ channels have already been described in giant algae (1, 5) and in protoplasts isolated from wheat mesophyll cells (13,14), Vicia faba guard cells (27,29) Protoplast Isolation. Terminal secondary pulvini from the fourth to ninth leaf (counting from the apex) were harvested 2 to 3 h after the beginning of the light period in the growth chamber, or 2 to 3 h after sunrise in the greenhouse.…”

Section: Abstracimentioning

confidence: 99%

“…K+ channels have already been described in giant algae (1,5) and in protoplasts isolated from wheat mesophyll cells (13,14), Vicia faba guard cells (27,29), carrot callus cells (14), and Asclepias 1 Supported by grant US-963-85 from the United States-Israel Binational Agricultural Research and Development Fund to N. M., R. L. S., and C. M., by grant 85-00259 from the United States-Israel Binational Science Fundation, Jerusalem to N. M., and by grant DMB83-04613 from the National Science Foundation to R. L. S. 2 Reprint requests may be sent to either N. M. or R. L. S.…”

Section: Abstracimentioning

confidence: 99%

Potassium Channels in Motor Cells of Samanea saman

Moran

Ehrenstein²,

Iwasa³

et al. 1988

Plant Physiol.

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114

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ABSTRACILeaflet movements in Samanea saman are driven by the shrinking and swelling of cells in opposing (extensor and flexor) regions of the motor organ (pulvinus). Changes in cell volume, in turn, depend upon large changes in motor cell content of K+, Cl and other ions. We performed patch-clamp experiments on extensor and flexor protoplasts, to determine whether their plasma membranes contain channels capable of carrying the large K currents that flow during leaflet movement. Recordings in the "whole-cell" mode reveal depolarization-activated K+ currents in extensor and flexor cells that increase slowly (t½ = ca. 2 seconds) and remain active for minutes. Recordings from excised patches reveal a single channel conductance of ca. 20 picosiemens in both cell types. The magnitude of the K+ currents is adequate to account quantitatively for K+ loss, previously measured in vivo during cell shrinkage. The K+ channel blockers tetraethylammonium (5 millimolar) or quinine (1 millimolar) blocked channel opening and decreased light-and dark-promoted movements of excised leaflets. These results provide evidence for the role of potassium channels in leaflet movement.Leaflet movements in nyctinastic (night closure) plants often involve significant changes in the volume and up to severalfold variation in the ionic content of motor cells in the pulvinus (reviewed in Ref. 21). These variations may occur in response to light, darkness, and an endogenous biological clock. Cells in the extensor region of the pulvinus take up K+ and Cl-as they swell during leaflet opening, and lose both ions as they shrink during leaflet closure, while cells in the opposing (flexor) region behave in the reverse manner (12,22,23,25,30,32).We undertook this study to examine a possible role for K+ channels in leaflet movement-related K+ fluxes and changes in cell volume in the nyctinastic legume Samanea saman. K+ channels have already been described in giant algae (1, 5) and in protoplasts isolated from wheat mesophyll cells (13,14), Vicia faba guard cells (27,29) Protoplast Isolation. Terminal secondary pulvini from the fourth to ninth leaf (counting from the apex) were harvested 2 to 3 h after the beginning of the light period in the growth chamber, or 2 to 3 h after sunrise in the greenhouse. Protoplasts were prepared by enzymic digestion of slices of extensor or flexor tissue (pooled separately), as described in (7) but with the following modifications. (a) The osmotic pressure of the pre-digestion solution was raised in two steps to 680 mosmol to ensure plasmolysis. (b) Pectolyase Y-23 (Seishin Pharmaceutical, Tokyo, Japan) was added to the digestion solution (which contained cellulase, pectinase and Driselase) to a final concentration of 0.2% (w/v). (c) A second purification step was added, as follows: the cells collected from the Ficoll interface were layered again on a sucrose gradient (2), spun at 60 to IOOg for 5 min, and collected and kept on ice for up to 24 h for patch-clamp experiments.Forty to fifty protoplasts of each type, flexor and ...

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Ionic Channels in Plant Protoplasts

Cited by 8 publications

References 21 publications

External pH effects on the depolarization-activated K channels in guard cell protoplasts of Vicia faba.

External pH effects on the depolarization-activated K channels in guard cell protoplasts of Vicia faba.

Tansley Review No. 21 Plant ion channels: whole‐cell and single channel studies

Potassium Channels in Motor Cells of Samanea saman

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