Evidence for an electrogenic ion transport pump in cells of higher plants

Higinbotham, Noe; Graves, J. S.; Davis, R. F.

doi:10.1007/bf01868016

Cited by 108 publications

(56 citation statements)

References 23 publications

(31 reference statements)

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“…This equation should hold for ions passively distributed or for cases in which the ion pumps are neutral. However, there is evidence with seedling tissues that a significant portion of the cell electropotential arises from a metabolically driven electrogenic pump (7,10). In this circumstance the equation would not be expected to fit experimental data on tissue having such transport.…”

Section: Resultsmentioning

confidence: 98%

Compartments and Fluxes of K⁺, NA⁺, and CL⁻ in Avena Coleoptile Cells

1970

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fluxes across the plasmalemma and the tonoplast. In the present study we report estimates of compartmental concentrations and fluxes in oat coleoptile tissue and present evidence that ion selectivity resides primarily in the plasmalemma. MATERIALS AND METHODSOat (Avena sativa L. cv. Victory) coleoptile segments were chosen for this work because they are cylinders averaging about six cells in thickness; thus the problems associated with diffusion from more deeply seated cells are minimized. Seedlings were grown in darkness at 25 C with a 20-min exposure to weak red light at 72 to 76 hr and coleoptiles were harvested at 96 hr. The substrate was vermiculite watered generously with a nutrient solution having the following composition in mM: KCI, 10; NaH2PO4, 9.04; Na2HPO4, 0.48; Ca(NO3)2, 10; MgSO4, 2.5.The pH was 5.3 to 5.5. The solution used for tracer loading and for efflux had the same composition.The upper 0.5 cm of the coleoptile was discarded, and the subjacent 2-cm portion-after removal of the enclosed leaf-was cut into 2.5-mm segments. These segments were pretreated in unlabeled nutrient solution for 4 to 8 hr except in experiment II where isotope loading began immediately upon completion of cutting. Each tissue sample consisted of about 35 segments weighing approximately 0.8 g. In two experiments, one done in duplicate, tracer loading was with 42K and 22Na; in another experiment done in duplicate, loading was with 42K and 36Cl. The specific radioactivity of the labeling solution at the start of washout was about 20,000 cpm,',ueq for 42K and 22Na; and for 36C1 about 5,000 cpm, 'geq. The loading period was 12 or 16 hr with each sample in a 125-ml flask containing 50 ml of solution agitated on a reciprocating shaker at 20 C. At the end of this period the segments were screened, gently blotted, then placed without rinsing into a cylindrical filter tube having a chamber of 29 mm diameter by 70 mm high, fitted with a drainage tap 8 mm in diameter; these also were mounted on a shaker. Aliquots of unlabeled nutrient solution (about 10 ml) were added and drained off periodically to provide measurements of tracer loss with time. Initially the washout periods were about 30 sec each but were gradually increased to 2 hr ( Figs. 1 and 2). The sum of the radioactivity values of the washout samples plus that remaining in the tissue at the end provides the measure of activity at to (i.e., at start of efflux).For assay of isotopes each drainage sample was evaporated to dryness in stainless steel planchets and counted with a NuclearChicago automatic planchet changer and D-47 gas flow detector. When "fCl was present, tris was added to prevent volatilization of Cl-. Initial counts included both 42K and 22Na or 42K and 36C1. Seven to 10 days later, after complete decay of 42K, another count was made of the 22Na or 36C1; thus the difference represented 42K activity only. All 42K counts were corrected for decay.Chemical assays of parallel tissue samples were made at the start of tracer loading, at the start of efflux, and at the ...

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Section: Resultsmentioning

confidence: 98%

Compartments and Fluxes of K⁺, NA⁺, and CL⁻ in Avena Coleoptile Cells

1970

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“…As illustrated for washed tissue, the PD recovers as the uncoupler is washed out. We will refer to that portion of the PD which is reversibly collapsed by uncoupling as the electrogenic PD; the base potential is the diffusion potential (3,4). Figure 2 shows a slight, nonsignificant increase in diffusion potential during the course of washing.…”

Section: Methodsmentioning

confidence: 99%

“…In other work, Higinbotham and associates have shown that a portion of the measured potential difference across the cytoplasmic layer of higher plant cells is electrogenic (4). Inhibitors or uncouplers of respiration collapse a significant portion of the cell potential, and this is attributed to failure of the energy supply for a metabolically driven ion or proton pump.…”

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Increase in Electrogenic Membrane Potential with Washing of Corn Root Tissue

Lin¹,

Hanson²

1974

Plant Physiol.

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There is now considerable evidence for the existence of electrogenic pumps, possibly as proton efflux pumps (3).As part of an inquiry into the mechanisms underlying the increased rates of solute absorption accompanying the washing of corn root tissue (5, 6), we have now determined the cell potential of epidermal cells of corn root tissue during washing. The entire increase in PD2 proves to be due to an electrogenic mechanism, the latter being operationally defined as that portion of the PD collapsed by the uncoupler FCCP. METHODS AND MATERIALSTwo-centimeter segments of primary corn seedling roots [Zea mavs L., WF9(Tms) X M14] were taken 0.5 to 2.5 cm.

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“…Higinbotham et al, 1970). In this article we describe for the first time measurements of electric potential difference (p.d.)…”

Section: mentioning

confidence: 99%

Transmembrane electric potential difference of germ tubes of arbuscular mycorrhizal fungi responds to external stimuli

Ayling

Smith

2000

New Phytologist

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Measurements of the electric potential difference across the hyphal wall and the cell membrane were made on external hyphae of three species of arbuscular mycorrhizal fungus Gigaspora margarita, Scutellospora calospora and Glomus coronatum and on germ tubes of Gi. margarita. The values of transmembrane electric potential difference recorded ("k40 mV) are less negative than those previously reported from hyphae of arbuscular mycorrhizal fungi closely associated with roots and from filamentous fungi. The external hyphae of arbuscular mycorrhizal fungi grown in soil had similar values of electric potential difference to those grown in soil-less culture, and to germ tubes. Thermodynamic calculations showed that despite these low values of electric potential difference, efficient high-affinity uptake of phosphate is possible. The transmembrane electric potential difference of germ tubes of Gi. margarita became more negative when plant root extract was added to the medium, showing for the first time that the early stages of interaction between plant and fungus occur via direct effects on the plasma membrane rather than via effects on gene expression. Addition of K + reversibly depolarized the transmembrane electric potential difference of germ tubes of Gi. margarita, indicating that despite the low electric potential difference the fungus has control over the permeability of the plasmamembrane to K + .

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Evidence for an electrogenic ion transport pump in cells of higher plants

Cited by 108 publications

References 23 publications

Compartments and Fluxes of K⁺, NA⁺, and CL⁻ in Avena Coleoptile Cells

Compartments and Fluxes of K⁺, NA⁺, and CL⁻ in Avena Coleoptile Cells

Increase in Electrogenic Membrane Potential with Washing of Corn Root Tissue

Transmembrane electric potential difference of germ tubes of arbuscular mycorrhizal fungi responds to external stimuli

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Evidence for an electrogenic ion transport pump in cells of higher plants

Cited by 108 publications

References 23 publications

Compartments and Fluxes of K+, NA+, and CL− in Avena Coleoptile Cells

Compartments and Fluxes of K+, NA+, and CL− in Avena Coleoptile Cells

Increase in Electrogenic Membrane Potential with Washing of Corn Root Tissue

Transmembrane electric potential difference of germ tubes of arbuscular mycorrhizal fungi responds to external stimuli

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Compartments and Fluxes of K⁺, NA⁺, and CL⁻ in Avena Coleoptile Cells

Compartments and Fluxes of K⁺, NA⁺, and CL⁻ in Avena Coleoptile Cells