Controls on <sup>22</sup>Na<sup>+</sup> Influx in Corn Roots

Jacoby, B.; Hanson, James A.

doi:10.1104/pp.77.4.930

Cited by 28 publications

(23 citation statements)

References 16 publications

(27 reference statements)

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“…3) is in agreement with other findings (10,15,20,26,27). This does not necessarily contradict the findings of Kent and Lauchli (18), who found that the tissue concentrations of Na in cotton seedlings were unaffected by external Ca2`concentrations at 200 mM NaCl.…”

Section: Methodssupporting

confidence: 83%

Influx of Na⁺, K⁺, and Ca²⁺ into Roots of Salt-Stressed Cotton Seedlings

Cramer¹,

Lynch²,

Läuchli³

et al. 1987

Plant Physiol.

272

121

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Section: Methodssupporting

confidence: 83%

Influx of Na⁺, K⁺, and Ca²⁺ into Roots of Salt-Stressed Cotton Seedlings

Cramer¹,

Lynch²,

Läuchli³

et al. 1987

Plant Physiol.

272

121

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“…It has long been known that transfer of root tissues of many plant species to cation uptake solutions without calcium causes rapid changes in ion uptake patterns, presumably as a result of membrane destabilization (7,12). Rates of sodium influx were considerably increased within 30 min of transfer of maize root segments to solutions without an external source of calcium (Table I).…”

Section: \5%mentioning

confidence: 84%

“…Segments were incubated for 30 min been invoked to explain concentration dependent influx kiix of sodium expressed as a percentage of control rates with netics (7,12). Thus, the percent inhibition of sodium uptake mm calcium concentration in the uptake solution (100%).…”

Section: \5%mentioning

confidence: 99%

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Sodium Does Not Compete with Calcium in Saturating Plasma Membrane Sites Regulating ²²Na Influx in Salinized Maize Roots

Zidan¹,

Jacoby²,

Ravina³

et al. 1991

Plant Physiol.

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Half maximal inhibition of sodium ('Na ) influx into maize (Zea mays L.) root segments incubated in solutions containing from 0.25 to 100 millimolar NaCI was consistently attained with external calcium activity at 0.26 ± 0.10 millimolar. Sodium ions do not appear to compete with calcium during initial binding to sites on the plasma membrane that participate in the regulation of sodium influx under saline conditions.Increasing the activity of calcium ions in the saline root media of glycophytic crop plants can reduce sodium accumulation and partially reverse the growth inhibition induced by excess salinity in the rhizosphere (2,4,5,8,15 (2) suggested that this could be the primary root response to salt stress. The displacement ofthese essential calcium ions by sodium would disrupt membrane stability thus accelerating efflux of intracellular solutes and influx of toxic sodium from the rhizosphere; additional calcium ions in the rhizosphere would reverse these processes by competing more effectively with sodium ions for calcium binding sites on the plasma membrane (2, 8, 9). Direct support for this hypothesis was initially provided by observations of NaCl induced displacement of surface Ca2" from intact cotton root hairs and maize root protoplasts, as visualized using microfluorometric techniques (2, 9). However, these techniques may be prone to interpretation errors and a later report suggested that the predominant effect of external salinization on calcium associated fluorescence in maize protoplasts was due to the release of calcium from intracellular membranes rather than its displacement from the plasma membrane surface (10). .N.). 331 An alternative method for investigating salinity effects on sodium influx into roots and its relation to calcium binding at the plasma membrane is described here. We assume that if sodium ions are able to competitively displace calcium from plasma membrane binding sites associated with the regulation of sodium influx, then the external calcium activity required to inhibit sodium influx should increase as external salinity is increased. If, alternatively, external salinity does not competitively displace calcium, then the calcium activity required to inhibit sodium influx should remain constant as external salinity is increased. To determine which mechanism is operative, we investigated the effects of a range of external concentrations of NaCl (0.25-100 mM) on rates on sodium (22Na) influx into washed maize root segments. Sodium influx at each NaCl concentration was assayed at several different calcium concentrations from 0 to 10 mM. Salinization of solutions increases their ionic strength. Such increases in ionic strength can progressively reduce the effective concentration and the physiologically effective chemical activity of calcium ions, through ion to ion interactions (1,3,6). Thus, instead of relating sodium influx to total calcium concentrations, we investigated the relationship between sodium influx and the chemical activity of the calcium ions in each of the...

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“…The reduction in cation influx by the addition of Ca 2ϩ ions is also important to the postulate that this transporter may play a role in the uptake of Na ϩ and in plant response to salinity. At the whole plant level it has been shown that the addition of Ca 2ϩ ameliorates Na ϩ toxicity (38), reduces Na ϩ uptake and inhibits translocation (39,40). At the cellular level it was recently shown that Ca 2ϩ partially abolishes the uptake of Na ϩ into wheat root cells through nonselective cation channels (41).…”

Section: Discussionmentioning

confidence: 99%

Molecular and functional characterization of a novel low-affinity cation transporter (LCT1) in higher plants

Schachtman

Kumar²,

Schroeder³

et al. 1997

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

175

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The transport of cations across membranes in higher plants plays an essential role in many physiological processes including mineral nutrition, cell expansion, and the transduction of environmental signals. In higher plants the coordinated expression of transport mechanisms is essential for specialized cellular processes and for adaptation to variable environmental conditions. To understand the molecular basis of cation transport in plant roots, a Triticum aestivum cDNA library was used to complement a yeast mutant deficient in potassium (K ؉ ) uptake. Two genes were cloned that complemented the mutant: HKT1 and a novel cDNA described in this report encoding a cation transporter, LCT1 (lowaffinity cation transporter). Analysis of the secondary structure of LCT1 suggests that the protein contains 8-10 transmembrane helices and a hydrophilic amino terminus containing sequences enriched in Pro, Ser, Thr, and Glu (PEST). The transporter activity was assayed using radioactive isotopes in yeast cells expressing the cDNA. LCT1 mediated low-affinity uptake of the cations Rb ؉ and Na ؉ , and possibly allowed Ca 2؉but not Zn 2؉ uptake. LCT1 is expressed in low abundance in wheat roots and leaves. The precise functional role of this cation transporter is not known, although the competitive inhibition of cation uptake by Ca 2؉ has parallels to whole plant and molecular studies that have shown the important role of Ca 2؉ in reducing Na ؉ uptake and ameliorating Na ؉ toxicity. The structure of this higher plant ion transport protein is unique and contains PEST sequences.

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Controls on ²²Na⁺ Influx in Corn Roots

Abstract: We have investipted the effects of hyperpolarization and depolariza-

Cited by 28 publications

References 16 publications

Influx of Na⁺, K⁺, and Ca²⁺ into Roots of Salt-Stressed Cotton Seedlings

Influx of Na⁺, K⁺, and Ca²⁺ into Roots of Salt-Stressed Cotton Seedlings

Sodium Does Not Compete with Calcium in Saturating Plasma Membrane Sites Regulating ²²Na Influx in Salinized Maize Roots

Molecular and functional characterization of a novel low-affinity cation transporter (LCT1) in higher plants

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Controls on 22Na+ Influx in Corn Roots

Abstract: We have investipted the effects of hyperpolarization and depolariza-

Cited by 28 publications

References 16 publications

Influx of Na+, K+, and Ca2+ into Roots of Salt-Stressed Cotton Seedlings

Influx of Na+, K+, and Ca2+ into Roots of Salt-Stressed Cotton Seedlings

Sodium Does Not Compete with Calcium in Saturating Plasma Membrane Sites Regulating 22Na Influx in Salinized Maize Roots

Molecular and functional characterization of a novel low-affinity cation transporter (LCT1) in higher plants

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Controls on ²²Na⁺ Influx in Corn Roots

Influx of Na⁺, K⁺, and Ca²⁺ into Roots of Salt-Stressed Cotton Seedlings

Influx of Na⁺, K⁺, and Ca²⁺ into Roots of Salt-Stressed Cotton Seedlings

Sodium Does Not Compete with Calcium in Saturating Plasma Membrane Sites Regulating ²²Na Influx in Salinized Maize Roots