Ion channels and ATP-driven pumps involved in ion transport across the tonoplast of sugarbeet vacuoles

Coyaud, Laurent; Kurkdjian, Armen; Kado, R. T.; Hedrich, Rainer

doi:10.1016/0005-2736(87)90304-x

Cited by 87 publications

(59 citation statements)

References 13 publications

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“…In insideout tonoplast patches, the most frequently observed channel showed a high conductance compared with typical plasma membrane channels. A high-conductance tonoplast channel has been reported in the guard cell tonoplast of V. faba (Hedrich et al, 1988) and in vacuole membranes of other tissues (Hedrich et al, 1986;Coyaud et al, 1987;Hedrich and Neher, 1987). Figure 1A (Fig.…”

Section: Cuard Cell Vacuoles Have An Outward-rectifying Cationic Channelmentioning

confidence: 89%

“…It has been suggested that slow-vacuolar-type channels might be involved in malate fluxes across the tonoplast (Hedrich et al, 1986;Coyaud et al, 1987;Hedrich and Neher, 1987). However, this is unlikely to be the case in onion guard cells, which are devoid of malate fluxes (Schnabl and Ziegler, 1977;Schnabl, 1980;Schnabl and Raschke, 1980).…”

Section: Discussionmentioning

confidence: 99%

“…They show a high unitary conductance ( 8 ) with a slow activation mode (about 180 pS in 200 ITLM KCI) and less selectivity than plasma membrane K+ channels (Hedrich et al, 1986;Coyaud et al, 1987;Hedrich and Neher, 1987). This low selectivity seems to vary with tissues.…”

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confidence: 99%

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A Cationic Channel in the Guard Cell Tonoplast of Allium cepa

Amodeo¹,

Escobar²,

Zeiger³

1994

Plant Physiol.

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Stomatal movements depend on an osmoregulation process in which swelling or shrinking of the guard cells opens or closes the stomatal pore. lons 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. Cuard 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 outwardrectifying 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*). l h e 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 firstlatency analysis of single-channel records in response to protocols with different prepulse duration indicated that this channel has more than one closed state.Stomatal movements regulate leaf CO, uptake and water loss in response to environmental signals. Volume changes in guard cells mediated by ion fluxes, and carbohydrate and organic acid biosynthesis cause changes in stomatal apertures that modulate leaf gas exchange (Zeiger, 1983;MacRobbie, 1988; Tallmann, 1992). Understanding of the ion flwes involved in this process should enhance our knowledge of the dynamics of stomatal movements and their regulation. Previous studies of ion fluxes in guard cells have focused on electrogenic pumps and ion channels at the plasma membrane. Several K+ channels have been characterized in detail (Schroeder et al., 1984(Schroeder et al., , 1987Schroeder, 1988). Anion and stretch-regulated channels have also been reported (Hedrich et al

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Section: Cuard Cell Vacuoles Have An Outward-rectifying Cationic Channelmentioning

confidence: 89%

Section: Discussionmentioning

confidence: 99%

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A Cationic Channel in the Guard Cell Tonoplast of Allium cepa

Amodeo¹,

Escobar²,

Zeiger³

1994

Plant Physiol.

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“…Upon addition of 5 ,M MIA to the bath, the single channel activity in the patch was diminished (Fig. 7B), although some openings were still recorded.…”

Section: Single Channel Currentsmentioning

confidence: 99%

“…A H+-coupled Na+ transport (Na+/H+ antiport) has been fairly well characterized in Beta vulgaris (3,4) and in barley (8). Passive sodium transport via voltage-dependent ion channels in the tonoplast has also been demonstrated in B. vulgaris (5,18). These ion channels are nonselective between Na+ and K+ and have a cation/anion selectivity of about 5:1.…”

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confidence: 99%

Tonoplast Ion Channels from Sugar Beet Cell Suspensions

Pantoja

Dainty²,

Blumwald³

1990

Plant Physiol.

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The properties of the vacuolar membrane (tonoplast) ion channels of sugar beet (Beta vulgaris) cell cultures were studied using the patch-clamp technique. Tonoplast currents displayed inward rectification in the whole vacuole and isolated outside-out patch configurations and permeability ratios PK+/PNa+ = 1 and PK+/PCI-= 5. Amiloride and two of its analogs, 5-(N-methyl-N-isobutyl)-amiloride and benzamil, inhibitors of Na+ channels in animal systems, blocked inward currents by reducing single-channel openings. Concentrations for 50% inhibition of vacuolar currents of 730 nanomolar, 130 nanomolar, and 1.5 micromolar for amiloride, benzamil, and 5-(N-methyl-N-isobutyl)-amiloride, respectively, were obtained from whole-vacuole recordings. The high inhibitory action (affinity) of amiloride and its analogs for the tonoplast cation channel suggests that these compounds could be used for the isolation and biochemical characterization of this protein.Plant vacuoles may occupy up to 90% of the cell volume. The vacuole has major roles in pH and ionic regulation of the cytoplasm, turgor regulation of the cell, and the storage and retrieval of both organic and inorganic nutrients. The vacuolar membrane, the tonoplast, plays an important role in controlling the ionic concentrations in the cell, particularly for halophytes and salt-tolerant glycophytes that accumulate high concentrations of sodium chloride in their vacuoles.Active (uphill) and passive (downhill) transport of sodium have been demonstrated in vacuoles and tonoplast vesicles isolated from beet and barley. Active sodium transport has been shown to be secondary, using the electrochemical potential difference for H+ generated by H+-transporting enzymes, ATPase (22), and pyrophosphatase (19), as the source of energy. A H+-coupled Na+ transport (Na+/H+ antiport) has been fairly well characterized in Beta vulgaris (3, 4) and in barley (8). Passive sodium transport via voltage-dependent ion channels in the tonoplast has also been demonstrated in B. vulgaris (5, 18). These ion channels are nonselective between Na+ and K+ and have a cation/anion selectivity of about 5:1. Moreover, tonoplast cation channels rectify, i.e. their conductance is much higher when the vacuolar membrane potential is negative with respect to the cytoplasm (18). Despite increasing evidence concerning the presence of ion channels with a high selectivity for cations, and the operation of a Na+/H+ antiport in the tonoplast from different plant species, the biochemical characterization of these transport proteins has not been accomplished. Biochemical efforts aimed at the identification and purification of these proteins have been hampered by the lack of specific ligands suitable for labeling the proteins' subunit(s). Our previous studies have shown that the diuretic drug amiloride acts as a competitive inhibitor ofthe vacuolar Na+/H+ antiport, similar to its effects in animal cells (2). However, amiloride is not a specific inhibitor of the Na+/H+ antiport; it also inhibits several Na+ transpor...

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