The Effect of Salinity on the Membrane Potential of Sunflower Roots

Çakirlar, Hüsnü; Bowling, D. J. F.

doi:10.1093/jxb/32.3.479

Cited by 37 publications

(18 citation statements)

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“…So, the activation of DAPCs and NSCCs most likely underlies the Na 1 -induced K 1 efflux. This is consistent with the strong NaCl-induced depolarization found in our experiments (Table I) and reported elsewhere for both root and leaf tissues (Cakirlar and Bowling, 1981;Babourina et al, 2000;Horie et al, 2001;Laurie et al, 2002;Shabala et al, 2003). This depolarization is caused by the massive Na 1 influx and preceding K 1 efflux, at least in intact Arabidopsis roots (Figs.…”

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confidence: 93%

Extracellular Ca2+ Ameliorates NaCl-Induced K+ Loss from Arabidopsis Root and Leaf Cells by Controlling Plasma Membrane K+-Permeable Channels

et al. 2006

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Calcium can ameliorate Na+ toxicity in plants by decreasing Na+ influx through nonselective cation channels. Here, we show that elevated external [Ca2+] also inhibits Na+-induced K+ efflux through outwardly directed, K+-permeable channels. Noninvasive ion flux measuring and patch-clamp techniques were used to characterize K+ fluxes from Arabidopsis (Arabidopsis thaliana) root mature epidermis and leaf mesophyll under various Ca2+ to Na+ ratios. NaCl-induced K+ efflux was not related to the osmotic component of the salt stress, was inhibited by the K+ channel blocker TEA+, was not mediated by inwardly directed K+ channels (tested in the akt1 mutant), and resulted in a significant decrease in cytosolic K+ content. NaCl-induced K+ efflux was partially inhibited by 1 mm Ca2+ and fully prevented by 10 mm Ca2+. This ameliorative effect was at least partially attributed to a less dramatic NaCl-induced membrane depolarization under high Ca2+ conditions. Patch-clamp experiments (whole-cell mode) have demonstrated that two populations of Ca2+-sensitive K+ efflux channels exist in protoplasts isolated from the mature epidermis of Arabidopsis root and leaf mesophyll cells. The instantaneously activating K+ efflux channels showed weak voltage dependence and insensitivity to external and internal Na+. Another population of K+ efflux channels was slowly activating, steeply rectifying, and highly sensitive to Na+. K+ efflux channels in roots and leaves showed different Ca2+ and Na+ sensitivities, suggesting that these organs may employ different strategies to withstand salinity. Our results suggest an additional mechanism of Ca2+ action on salt toxicity in plants: the amelioration of K+ loss from the cell by regulating (both directly and indirectly) K+ efflux channels.

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confidence: 93%

Extracellular Ca2+ Ameliorates NaCl-Induced K+ Loss from Arabidopsis Root and Leaf Cells by Controlling Plasma Membrane K+-Permeable Channels

et al. 2006

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“…Cakirlar and Bowling 1981;Kourie and Findlay 1990) so that channels activated by depolarisation such as the anion OR may play an important role during increases in salinity. The anion OR appears to be sensitive to intracellular calcium concentration (directly or indirectly), since it was observed more often with higher intracellular calcium concentrations.…”

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confidence: 99%

A channel that allows inwardly directed fluxes of anions in protoplasts derived from wheat roots

Skerrett

Tyerman

1994

Planta

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Abstract. An anion channel that only allows outward current flow (anion influx) has been identified in protoplasts derived from wheat (Triticum aestivum L., Triticum turgidum L.) roots. The anion outward rectifier (anion OR) measured by patch-clamp of whole cells activated very quickly, usually reaching a steady-state level in less than 100 ms and was easily distinguished from the cation outward rectifier (cation OR) which activated more slowly during membrane depolarisation. The anion OR is permeable to NO 3 and CI, moderately permeable to I-, and relatively impermeable to H2PO 4 and C104 . An anomalous mole-fraction effect between C104 and C1-was observed on the outward current, indicating that the channel is a multi-ion pore. The anion OR is gated by both voltage and external anion concentration such that it activates near to the equilibrium potential for the permeant anion. It activated at more negative membrane potentials when NO 3 was substituted for C1 in the external medium, indicating that the channel may function to allow NO 3 influx under luxuriant external NO 3-concentrations. For most experiments, K + and C1-were the main cation and anion in solution, and under these conditions it appeared likely that the anion OR functioned in membrane-potential regulation by facilitating a C1 influx at membrane potentials more positive than the chloride reversal potential (Ect). If Ecl was more negative than the K + reversal potential (EK) then the anion OR dominated but both the anion and cation ORs occurred together when the membrane potential difference (Vm) was positive of both Ecl and EK. The cation OR was inhibited by increasing external C1 concentrations, but the anion OR was not affected by external K + or Na + concentration. The anion-transport inhibitors, zinc and phenylglyoxal were ineffective in blocking the anion OR. 4,4'-Diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) irreversibly blocked about 34% of the current when applied Abbreviations: Bath = solution bathing the extracellular face of the membrane; DIDS = (4,4'-diisothiocyanostilbene-2,2'-disulfonic acid); Ex = reversal potential for ion x; OR = outward rectifier; Pip = solution inside the pipette; TEAC1 = (tetraethyl-ammonium chloride); Vm = membrane potential difference Correspondence to: S.D. Tyerman; FAX: 61 (8) 2013015 extracellularly at a concentration of 25 gM, and about 69% at a concentration of 200 gM. However, DIDS (200 gM) also occasionally acted as an irreversible blocker of the cation OR. Perchlorate blocked irreversibly 75% of the current at an external concentration of 10 mM and did not block the cation OR. Whole-cell currents also indicated that the anion OR was insensitive to external pH(pH = 5-7) and calcium concentration ([Ca 2+] =0.1-10 mM). Increasing intracellular calcium concentration significantly increased the occurrence of the fast outward current in whole cells (P < 0.005, X 2 test). With approximately 10 nM calcium inside the cell the anion outward current was observed in 64% (n = 45) of cells and with 50 nM calcium...

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“…The cation outward rectifier channel is characterized by its strong voltage dependence of opening, causing it to dominate the membrane conductance when the membrane potential goes more positive than the reversal potential ofthe channel, which is usually very close to the EK3. In glycophytes, the membrane depolarizes in response to external NaCl, generally to membrane potentials at or more positive than EK (3,17). Depolar-ization will open the cation outward rectifier channels and Na+ could move into the cell at a rate governed by the electrochemical gradient for Na+ and the effective permeability of the channels to Na+.…”

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The K⁺/Na⁺ Selectivity of a Cation Channel in the Plasma Membrane of Root Cells Does Not Differ in Salt-Tolerant and Salt-Sensitive Wheat Species

Schachtman¹,

Tyerman²,

Terry³

1991

Plant Physiol.

124

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The characteristics of cation outward rectifier channels were studied in protoplasts from wheat root (Triticum aestivum L. and Triticum turgidum L.) cells using the patch clamp technique. The cation outward rectifier channels were voltage-dependent with a single channel conductance of 32 ± I picosiemens in 100 millimolar KCI. Whole-cell currents were dominated by the activity of the cation outward rectifiers. The time-and voltage-dependence of these currents was accounted for by the summed behavior of individual channels recorded from outside-out detached patches. The K+/Na+ permeability ratio of these channels was measured in a salt-sensitive and salt-tolerant genotype of wheat that differ in rates of Na+ accumulation, using a voltage ramp protocol on protoplasts in the whole-cell configuration. Permeability ratios were calculated from shifts in reversal potentials following ion substitutions. There were no significant differences in the K+/Na+ permeability ratios of these channels in root cells from either of the two genotypes tested. The permeability ratio for K+/Cl-was greater than 50:1. The K+/Na+ permeability ratio averaged 30:1, which is two to four times more selective than the same type of channel in guard cells and suspension culture cells. Lowering the Ca2+ concentration in the bath solution to 0.1 millimolar in the presence of 100 millimolar Na+ had no significant effect on the K+/Na+ permeability ratios of the channel. It seems unlikely that the mechanism of salt tolerance in wheat is based on differences in the K+/Na+ selectivity of these channels.In saline conditions, most salt-tolerant monocotyledonous plants accumulate lower amounts of sodium in their leaves than salt-sensitive monocotyledonous plants (1). Salt-tolerant genotypes of wheat have been shown to transport less sodium from roots to shoots than do salt-sensitive genotypes, both in the long term (24) and in the short term (5). There is only indirect evidence for a sodium-specific effect on growth in the long term; wheat plants grown in high sodium chloride solutions have lower growth rates than those grown in high

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The Effect of Salinity on the Membrane Potential of Sunflower Roots

Cited by 37 publications

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Extracellular Ca2+ Ameliorates NaCl-Induced K+ Loss from Arabidopsis Root and Leaf Cells by Controlling Plasma Membrane K+-Permeable Channels

Extracellular Ca2+ Ameliorates NaCl-Induced K+ Loss from Arabidopsis Root and Leaf Cells by Controlling Plasma Membrane K+-Permeable Channels

A channel that allows inwardly directed fluxes of anions in protoplasts derived from wheat roots

The K⁺/Na⁺ Selectivity of a Cation Channel in the Plasma Membrane of Root Cells Does Not Differ in Salt-Tolerant and Salt-Sensitive Wheat Species

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The Effect of Salinity on the Membrane Potential of Sunflower Roots

Cited by 37 publications

References 0 publications

Extracellular Ca2+ Ameliorates NaCl-Induced K+ Loss from Arabidopsis Root and Leaf Cells by Controlling Plasma Membrane K+-Permeable Channels

Extracellular Ca2+ Ameliorates NaCl-Induced K+ Loss from Arabidopsis Root and Leaf Cells by Controlling Plasma Membrane K+-Permeable Channels

A channel that allows inwardly directed fluxes of anions in protoplasts derived from wheat roots

The K+/Na+ Selectivity of a Cation Channel in the Plasma Membrane of Root Cells Does Not Differ in Salt-Tolerant and Salt-Sensitive Wheat Species

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The K⁺/Na⁺ Selectivity of a Cation Channel in the Plasma Membrane of Root Cells Does Not Differ in Salt-Tolerant and Salt-Sensitive Wheat Species