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

Tester, Mark

doi:10.1111/j.1469-8137.1990.tb00403.x

Cited by 301 publications

(176 citation statements)

References 254 publications

(317 reference statements)

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“…Significant progress has been made in understanding the importance of ion channels in ion transport across the membranes. Ion channels are biologically very active proteins that permit rapid and selective transport of ions depending on their opening and closure status (Tester, 1990). Ion channel proteins contain reactive kSH groups, and the activity of the channel is dependent on the redox status of these kSH groups.…”

Section: Alterations In Ion Absorptionmentioning

confidence: 99%

Tansley Review No. 111

2000

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Zinc deficiency is one of the most widespread micronutrient deficiencies in plants and causes severe reductions in crop production. There are a number of physiological impairments in Zn-deficient cells causing inhibition of the growth, differentiation and development of plants. Increasing evidence indicates that oxidative damage to critical cell compounds resulting from attack by reactive O # species (ROS) is the basis of disturbances in plant growth caused by Zn deficiency. Zinc interferes with membrane-bound NADPH oxidase producing ROS. In Zn-deficient plants the iron concentration increases, which potentiates the production of free radicals. The Zn nutritional status of plants influences photooxidative damage to chloroplasts, catalysed by ROS. Zinc-deficient leaves are highly light-sensitive, rapidly becoming chlorotic and necrotic when exposed to high light intensity. Zinc plays critical roles in the defence system of cells against ROS, and thus represents an excellent protective agent against the oxidation of several vital cell components such as membrane lipids and proteins, chlorophyll, SH-containing enzymes and DNA. The cysteine, histidine and glutamate or aspartate residues represent the most critical Znbinding sites in enzymes, DNA-binding proteins (Zn-finger proteins) and membrane proteins. In addition, animal studies have shown that Zn is involved in inhibition of apoptosis (programmed cell death) which is preceded by DNA and membrane damage through reactions with ROS.

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Section: Alterations In Ion Absorptionmentioning

confidence: 99%

Tansley Review No. 111

2000

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“…Entry of Ca2+ into the cytosol is probably a passive process mediated by ion channels (Tester, 1990). Two Ca2+ channels have been identified in the tonoplast using a combination of patch clamping and in vitro studies with membrane vesicles (Johannes et al, 1992).…”

Section: Introductionmentioning

confidence: 99%

Membrane potential‐dependent calcium transport in right‐side‐out plasma membrane vesicles from Zea mays L. roots

et al. 1994

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SummaryRight-side-out plasma membrane vesicles isolated from Zea mays roots were used to study membrane potential (Av)-dependent Ca2+ transport. Membrane potentials were imposed on the vesicles using either K+ concentration gradients and valinomycin or SCNconcentration gradients, and the size of the imposed A v was measured with ['4C]tetraphenylphosphonium. Uptake of 45Ca2+ into the vesicles was stimulated by inside-negative Ay. The rate of transport increased to a maximum at a A y of about -80 mV and then declined at more negative Av. When extravesicular Ca2+ concentration was varied, uptake was maximal in the range 100-200 pM Ca2+. Neither dihydropyridine nor phenylalkylamine Ca2+ channel blockers had any effect on Ca2+ uptake but 30 pM ruthenium red was completely inhibitory with half maximal inhibition at 10-15 pM ruthenium red. Calcium transport was also inhibited by inorganic cations. Zn2+, Gd3+ and Mg2+ inhibited by a maximum of 30% while La3+, Nd3+ and Mn2+ inhibited by 70%. The inhibitory effects of La3+ and Gd3+ were additive. Lanthanum-insensitive Ca2+ tive Ca2+ transport was totally inhibited by 80 pM Gd3+ and showed maximum activity at a A~J of -60 mV, with less uptake at both higher and lower Av. Lanthanum and Gd3+ also inhibited Ca2+ uptake into protoplasts isolated from Zea roots and their individual and combined effects were similar in extent to those observed with plasma membrane vesicles. It is concluded that

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“…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%

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

Cited by 301 publications

References 254 publications

Tansley Review No. 111

Tansley Review No. 111

Membrane potential‐dependent calcium transport in right‐side‐out plasma membrane vesicles from Zea mays L. roots

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

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