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  • 1
    Electronic Resource
    Electronic Resource
    Blue light-induced apoplastic acidification of Arabidopsis thaliana guard cells: Inhibition by ABA is mediated through protein phosphatases (1998)
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 103 (1998), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The phytohormone abscisic acid (ABA) inhibits blue light-induced apoplastic acidification of guard cells. The signal transduction pathway of ABA, mediating this response, was studied using ABA-insensitive (abi) mutants of Arabidopsis thaliana. Apoplastic acidification was monitored with a flat tipped pH-electrode placed on epidermal strips, in which only guard cells were viable. Blue light-induced apoplastic acidification was reduced by vanadate and diethylstilbestrol (DES), indicating involvement of plasma membrane-bound H+-ATPases. In wild type epidermal strips, ABA reduced blue light-induced acidification to 63%. The inhibition did not result from an increased cytoplasmic free Ca2+ concentration in guard cells, since factors that increase the Ca2+ concentration stimulated apoplastic acidification. Apoplastic acidification was not inhibited by ABA in abi1 and abi2 mutants. In abi1 epidermal strips ABA had no effect on the acidification rate, while it stimulated apoplastic acidification in abi2. The ABA response in both mutants could be partially restored with protein kinase and phosphatase inhibitors. The abi1 guard cells became ABA responsive in the presence of okadaic acid, a protein phosphatase inhibitor. In abi2 guard cells the wild type ABA response was partially restored by K-252a, a protein kinase inhibitor. Apoplastic inhibition is thus mediated through the protein phosphatases encoded by ABI1 and ABI2. The results with protein kinase and protein phosphatase inhibitors indicate that ABI1 and ABI2 are involved in separate signal transduction pathways.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.1998.1030404.x
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of abscisic acid on stomatal opening in isolated epidermal strips of abi mutants of Arabidopsis thaliana (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 95 (1995), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abscisic acid-insensitive mutants of Arabidopsis thaliana L. var. Landsberg erecta were selected for their decreased sensitivity to ABA during germination. Two of these mutants, abi-1 and abi-2, display a wilty phenotype as adult plants, indicating disturbed water relations. Experiments were undertaken to find out if this results from insensitivity of mutant stomates to ABA.Growth conditions and methods to isolate epidermal strips were optimized to study stomatal movement. Wild type stomates required external ionic conditions comparable to those found for other species such as Commelina communis. The largest light-induced opening of A. thaliana stomates was found at an external KCl concentration of 50 mM. Stomatal apertures were increased by lowering external Ca2+ to 0.05 mM. The apertures of stomates incubated with 10 μM ABA were not altered by changes in Ca2+ from 0.05 to 1.0 mM.Stomates of all abi mutants showed a light-stimulated stomatal opening. The opening of wild type and abi-3 stomates was inhibited by ABA, while stomates of abi-1 and abi-2 did not respond to ABA. The insensitivity of abi-1 and abi-2 stomates to ABA may thus explain the observed disturbed water relations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1995.tb00851.x
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  • 3
    Electronic Resource
    Electronic Resource
    ATPase activity of isolated plasma membrane vesicles of leaves of Elodea as affected by thiol reagents and NADH/NAD+ ratio (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 76 (1989), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The goal of this study was to test the hypothesis that the plasma membrane-bound ATPase activity is influenced by the redox poise of the cytoplasm. Purified plasma membrane vesicles from leaves of Elodea canadensis Michx. and E. nuttallii (Planch.) St. John were isolated using an aqueous polymer two-phase batch procedure. The distribution of marker enzyme activities confirmed the plasma membrane origin of the vesicles. The vesicles exhibited NADH-ferricyanide reductase activity, indicating the presence of a redox chain in the plasma membrane. The K+, Mg2+-ATPase activity associated with these vesicles was inhibited by the sulfhydryl reagents N-ethylmaleimide and glutathione (GSSG). Furthermore the activity was inhibited by NAD+. This inhibition by NAD+ was relieved by increasing the NADH/NAD+ ratio. The possibility that the ATPase activity is regulated by the cytoplasmic NAD(P)H/ NAD(P)+ ratio is discussed, as well as the role of a plasma membrane-bound redox chain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1989.tb06207.x
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  • 4
    Electronic Resource
    Electronic Resource
    Na+/H+ antiport activity in tonoplast vesicles from roots of the salt-tolerant Plantago maritima and the salt-sensitive Plantago media (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 82 (1991), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Plantago species differ in their strategy towards salt stress, a major difference being the uptake and distribution of Na+ ions. A salt-sensitive (Plantago media L.) and a salt-tolerant (P. maritima L.) species were compared with respect to Na+/H+ antiport activities at the tonoplast. After exposure of the plants to 50 mM NaCl for 6 days isolated tonoplast vesicles of P. maritima showed Na+/H+ antiport activity with saturation kinetics and a Km of 2.4 mM Na+, NaCl-grown P. media and the control plants of both species showed no antiport activity. Selectivity of the antiport system for Na+ was high and was determined by adding different chloride salts after formation of a Δ pH in the vesicles. Specific tonoplast ATPase activities were similar in the two species and did not alter after exposure to NaCl stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1991.tb00078.x
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  • 5
    Electronic Resource
    Electronic Resource
    Light-induced membrane potential changes of epidermal and mesophyll cells in growing leaves of Pisum sativum (1995)
    Springer
    Planta 197 (1995), S. 127-134 
    Details
    ISSN: 1432-2048
    Keywords: Argenteum mutant ; Epidermal cells ; Light ; Membrane potential ; Mesophyll cells ; Pisum (mutant)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Light transiently depolarizes the membrane of growing leaf cells. The ionic basis for changes in cell membrane electrical potentials in response to light has been determined separately for growing epidermal and mesophyll cells of the argenteum mutant of pea (Pisum sativum L.). In mesophyll cells light induces a large, transient depolarization that depends on the external Cl− concentration, is unaffected by changes in the external Ca2+ or K+ concentration, is stimulated by K+-channel blockers tetraethylammonium (TEA+) and Ba2+, and is inhibited by 3-(3′-4′-dichlorophenyl)-1,1-dimethylurea (DCMU). In isolated epidermal tissue, light induces a small, transient depolarization followed by a hyperpolarization of the membrane potential. The depolarization is enhanced by increasing the external Ca2+ concentration and by addition of Ba2+, and is not sensitive to DCMU. Epidermal cells in contact with mesophyll display a depolarization resembling the response of the underlying mesophyll cells. The light-induced depolarization in mesophyll cells seems to be mediated by an increased efflux of Cl− while the membrane-potential changes in epidermal strips reflect changes in the fluxes of Ca2+ and in the activity of the proton-pumping ATPase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00239948
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  • 6
    Electronic Resource
    Electronic Resource
    Ion channels in guard cells of Arabidopsis thaliana (L.) Heynh. (1997)
    Springer
    Planta 202 (1997), S. 18-27 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Arabidopsis guard cell ; Channel blocker (barium ; verapamil) ; Guard cell (physiological state) ; Potassium channel (inward rectifier ; slow and rapid outward rectifier) ; Voltage clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Despite the availability of many mutants for signal transduction, Arabidopsis thaliana guard cells have so far not been used in electrophysiological research. Problems with the isolation of epidermal strips and the small size of A. thaliana guard cells were often prohibiting. In the present study these difficulties were overcome and guard cells were impaled with double-barreled microelectrodes. Membrane-potential recordings were often stable for over half an hour and voltage-clamp measurements could be conducted. The guard cells were found to exhibit two states. The majority of the guard cells had depolarized membrane potentials, which were largely dependent on external K+ concentrations. Other cells displayed spontaneous transitions to a more hyperpolarized state, at which the free-running membrane potential (Em) was not sensitive to the external K+ concentration. Two outward-rectifying conductances were identified in cells in the depolarized state. A slow outward-rectifying channel (s-ORC) had properties resembling the K+-selective ORC of Vicia faba guard cells (Blatt, 1988, J Membr Biol 102: 235–246). The activation and inactivation times and the activation potential, all depended on the reversal potential (Erev) of the s-ORC conductance. The s-ORC was blocked by Ba2+ (K1/2 = 0.3–1.3mM) and verapamil (K1/2 = 15–20 μM). A second rapid outward-rectifying conductance (r-ORC) activated instantaneously upon stepping the voltage to positive values and was stimulated by Ba2+. Inward-rectifying channels (IRC) were only observed in cells in the hyperpolarized state. The activation time and activation potential of this channel were not sensitive to the external K+ concentration. The slow activation of the IRC (t1/2 ≈ 0.5 s) and its negative activation potential (Vthreshold = −155 mV) resemble the values found for the KAT1 channel expressed in Saccharomyces cerevisiae (Bertl et al., 1995, Proc Natl Acad Sci USA 92: 2701–2705). The results indicate that A. thaliana guard cells provide an excellent system for the study of signal transduction processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050098
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  • 7
    Electronic Resource
    Electronic Resource
    The membrane potential of Arabidopsis thaliana guard cells; depolarizations induced by apoplastic acidification (1998)
    Springer
    Planta 205 (1998), S. 100-112 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Apoplastic pH ; Arabidopsis guard cell ; Membrane potential ; Potassium channel (inward rectifier ; slow outward rectifier) ; Stable states (hyperpolarized ; depolarized) ; Voltage clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The apoplastic pH of guard cells probably acidifies in response to light, since light induces proton extrusion by both guard cells and epidermal leaf cells. From the data presented here, it is concluded that these apoplastic pH changes will affect K+ fluxes in guard cells of Arabidopsis thaliana (L.) Heynh. Guard cells of this species were impaled with double-barrelled microelectrodes, to measure the membrane potential (Em) and the plasma-membrane conductance. Guard cells were found to exhibit two states with respect to their Em, a depolarized and a hyperpolarized state. Apoplastic acidification depolarized Em in both states, though the origin of the depolarization differed for each state. In the depolarized state, the change in Em was the result of a combined pH effect on instantaneously activating conductances and on the slow outward rectifying K+ channel (s-ORC). At a more acidic apoplastic pH, the current through instantaneously activated conductances became more inwardly directed, while the maximum conductance of s-ORC decreased. The effect on s-ORC was accompanied by an acceleration of activation and deactivation of the channel. Experiments with acid loading of guard cells indicated that the effect on s-ORC was due to a lowered intracellular pH, caused by apoplastic acidification. In the hyperpolarized state, the pH-induced depolarization was due to a direct effect of the apoplastic pH on the inward rectifying K+ channel. Acidification shifted the threshold potential of the channel to more positive values. This effect was accompanied by a decrease in activation times and an increase of deactivation times, of the channel. From the changes in Em and membrane conductance, the expected effect of acidification on K+ fluxes was calculated. It was concluded that apoplastic acidification will increase the K+-efflux in the depolarized state and reduce the K+-influx in the hyperpolarized state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050301
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  • 8
    Electronic Resource
    Electronic Resource
    Inhibition of inward rectifying tonoplast channels by a vacuolar factor: Physiological and kinetic implications (1991)
    Springer
    The journal of membrane biology 122 (1991), S. 251-258 
    Details
    ISSN: 1432-1424
    Keywords: patch-clamp ; plant vacuole ; single-channel inhibition ; kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Regulation of ion-channel activity must take place in order to regulate ion transport. In case of tonoplast ion channels, this is possible on both the cytoplasmic and the vacuolar side. Isolated vacuoles of youngVigna unguiculata seedlings show no or hardly any channel activity at tonoplast potentials 〉80 mV, in the vacuole-attached configuration. When the configuration is changed to an excised patch or whole vacuole, a fast (excised patch) or slow (whole vacuole) increase of inward rectifying channel activity is seen. This increase is accompanied by a shift in the voltage-dependent gating to less hyperpolarized potentials. In the whole vacuole configuration the level of inward current increases and also the activation kinetics changes. Induction of channel activity takes up to 20 min depending on the age of the plants used and the diameter of the vacuole. On the basis of the estimated diffusion velocities, it is hypothesized that a compound with a mol wt of 20,000 to 200,000 is present in vacuoles of young seedlings, which shifts the population of channels to a less voltage-sensitive state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871425
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  • 9
    Electronic Resource
    Electronic Resource
    The kinetics of NH4 + and NO3 − uptake by Douglas fir from single N-solutions and from solutions containing both NH4 + and NO3 − (1993)
    Springer
    Plant and soil 151 (1993), S. 91-96 
    Details
    ISSN: 1573-5036
    Keywords: kinetic parameters ; NH4 + ; NO3 − ; Pseudotsuga menziesii
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The kinetics of NH4 + and NO3 − uptake in young Douglas fir trees (Pseudotsuga menziesii [Mirb.] Franco) were studied in solutions, containing either one or both N species. Using solutions containing a single N species, the Vmax of NH4 + uptake was higher than that of NO3 − uptake. The Km of NH4 + uptake and Km of NO3 − uptake differed not significantly. When both NH4 + and NO3 − were present, the Vmax for NH4 + uptake became slightly higher, and the Km for NH4 + uptake remained in the same order. Under these conditions the NO3 − uptake was almost totally inhibited over the whole range of concentrations used (10–1000 μM total N). This inhibition by NH4 + occurred during the first two hours after addition. ei]{gnA C}{fnBorstlap}
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00010789
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  • 10
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    The membrane potential of Arabidopsis thaliana guard cells; depolarizations induced by apoplastic acidification (1998)
    Springer
    Details
    Publication Date: 1998-04-22
    Print ISSN: 0032-0935
    Electronic ISSN: 1432-2048
    Topics: Biology
    Published by Springer
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