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  • 1
    Electronic Resource
    Electronic Resource
    Effect of abscisic acid on membrane potential and transport of glucose and glycine in Lemna gibba G1 (1980)
    Springer
    Planta 148 (1980), S. 256-261 
    Details
    ISSN: 1432-2048
    Keywords: Abscisic acid ; Auxin ; Glucose-transport ; Glycine-transport ; Lemna ; Membrane potential ; Respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The membrane potential of Lemna gibba G1 was measured with a microelectrode; glucose and glycine uptake were measured with 14C-labeled substances. The membrane potential was increased by 85 mV on the average, after the plants had been pretreated with 10 μM abscisic acid (ABA) for more than 30 min. This effect is not linked to the endogenous level of soluble sugars. The concentration of these soluble sugars was increased to more than 200% by pretreatment of the plants with ABA, however, the respiration of the plants was not affected. ABA stimulated uptake of glucose and glycine. Glucose- and glycine-dependent depolarization and repolarization of the membrane was altered: depolarization was less and repolarization was slower; during uptake of glycine, the first typical phase of repolarization was suppressed. The data suggest that ABA interferes with the primary steps of substrate uptake.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00380036
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  • 2
    Electronic Resource
    Electronic Resource
    Electron transport across the plasmalemma of Lemna gibba G1 (1986)
    Springer
    Planta 169 (1986), S. 251-259 
    Details
    ISSN: 1432-2048
    Keywords: Electron transport ; Ferricyanide reduction ; Lemna ; Membrane potential ; Proton transport ; Sulfate uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Lemna gibba L., grown in the presence or absence of Fe, reduced extracellular ferricyanide with a V max of 3.09 μmol · g-1 fresh weight · h-1 and a K m of 115 μM. However, Fe3+-ethylenediaminetetraacetic acid (EDTA) was reduced only after Fe-starvation. External electron acceptors such as ferricyanide, Fe3+-EDTA, 2,6-dichlorophenol indophenol or methylene blue induced a membrane depolarization of up to 100 mV, but electron donors such as ferrocyanide or NADH had no effect. Light or glucose enhanced ferricyanide reduction while the concomitant membrane depolarization was much smaller. Under anaerobic conditions, ferricyanide had no effect on electrical membrane potential difference (Em). Ferricyanide reduction induced H+ and K+ release in a ratio of 1.16 H++1 K+/2 e- (in +Fe plants) and 1.28 H++0.8 K+/2 e- (in -Fe plants). Anion uptake was inhibited by ferricyanide reduction. It is concluded that the steady-state transfer of electrons and protons proceeds by separate mechanisms, by a redox system and by a H+-ATPase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392322
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  • 3
    Electronic Resource
    Electronic Resource
    Membrane potential changes during transport of hexoses in Lemna gibba G1 (1978)
    Springer
    Planta 138 (1978), S. 263-270 
    Details
    ISSN: 1432-2048
    Keywords: ATP ; Hexose transport ; Lemna ; Membrane potential ; Photosynthesis ; Respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The membrane potential (pd) of duck weed (Lemna gibba G1) proved to be energy dependent. At high internal ATP levels of 74 to 105 nmol ATP g-1 FW, pd was between -175 and -265 mV. At low ATP levels of 23 to 46 nmol ATP g-1 FW, pd was low, about -90 to -120 mV at pH 5.7, but -180 mV at pH 8. Upon addition of glucose in the dark or by light energy the low pd recovered to the high values. The active component of the pd was depolarized by the addition of hexoses in the dark and in the light. Hexose-dependent depolarization of the pd (=Δ pd) followed a saturation curve similar to active hexose influx kinetics. Depolarization of the pd recovered in the dark even in the presence of the hexoses and with a 10fold enhancement in the light. Depolarization and recovery could be repeated several times with the same cell. Glucose uptake caused a maximum depolarization of 133 mV, fructose uptake half that amount, sucrose had the same effect as glucose. During 3-O-methylglucose and 2-deoxyglucose uptake the depolarizing effect was only slightly lower. The pd remained unchanged in the presence of mannitol. The glucose dependent Δ pd and especially the rate of pd recovery proved to be pH-dependent between pH 4 and pH 8. It was independent of the presence of 1 mM KCl. Although no Δ pH could be measured in the incubation medium, these results can be best explained by a H+-hexose cotransport mechanism powered by active H+ extrusion at the plasmalemma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00386821
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  • 4
    Electronic Resource
    Electronic Resource
    pH and membrane-potential changes during glucose uptake inLemna gibba G1 and their response to light (1980)
    Springer
    Planta 149 (1980), S. 321-326 
    Details
    ISSN: 1432-2048
    Keywords: Glucose cotransport ; H+-glucose cotransport ; Lemna ; Membrane potential ; pH changes, external ; Transport, glucose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Extracellular pH was measured with a microelectrode positioned over the lower surface of singleLemna gibba plants. Upon addition of glucose, a transient extracellular alkalinization occurred. Saturated extracellular pH changes were observed with 5 mM glucose. Simultaneously, the membrane potential difference of −250 mV in the dark measured with intracellular glass micropipettes, trnasiently decreased by 105 mV. Uptake of [14C]glucose and extracellular alkalinization was enhanced by light whereas glucose-induced membrane-potential changes were reduced in the light and became even smaller with increasing the preillumination time. Glucose uptake was optimal at pH 6. The results are taken as further evidence in favor of H+-glucose cotransport inLemna.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00571164
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  • 5
    Electronic Resource
    Electronic Resource
    Phosphate uptake inLemna gibba G1: energetics and kinetics (1984)
    Springer
    Planta 161 (1984), S. 46-52 
    Details
    ISSN: 1432-2048
    Keywords: Lemna (phosphate uptake) ; Membrane potential ; Proton/phosphate cotransport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Phosphate uptake was studied by determining [32P]phosphate influx and by measurements of the electrical membrane potential in duckweed (Lemna gibba L.). Phosphate-induced membrane depolarization (ΔE m ) was controlled by the intracellular phosphate content, thus maximal ΔE m by 1 mM H2PO 4 - was up to 133 mV after 15d of phosphate starvation. The ΔE m was strongly dependent on the extracellular pH, with a sharp optimum at pH 5.7. It is suggested that phosphate uptake is energized by the electrochemical proton gradient, proceeding by a 2H+/H2PO 4 - contransport mechanism. This is supported also by the fusicoccin stimulation of phosphate influx. Kinetics of phosphate influx and of ΔE m , which represent mere plasmalemma transport, are best described by two Michaelis-Menten terms without any linear components.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00951459
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  • 6
    Electronic Resource
    Electronic Resource
    Evidence for proton/sulfate cotransport and its kinetics inLemna gibba G1 (1984)
    Springer
    Planta 161 (1984), S. 53-60 
    Details
    ISSN: 1432-2048
    Keywords: Lemna (sulfate uptake) ; Membrane potential ; Proton/sulfate cotransport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Sulfate uptake into duckweed (Lemna gibba G1) was studied by means of [35S]sulfate influx and measurements of electrical membrane potential. Uptake was strongly regulated by the intracellular content of soluble sulfate. At the onset of sulfate uptake the membrane potential was transiently depolarized. Fusicoccin stimulated uptake up to 165% of the control even at pH 8. It is suggested that sulfate uptake is energized in the whole pH range by a 3H+/sulfate cotransport mechanism. Kinetics of sulfate uptake and sulfate-induced membrane depolarization in the concentration range of 5 μM to 1 mM sulfate at pH 5.7 was best described by two Michaelis-Menten terms without any linear component. The second system had a lower affinity for sulfate and was fully active only at sufficiently high proton concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00951460
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  • 7
    Electronic Resource
    Electronic Resource
    Der Einfluß von Natrium- und Kaliumionen auf die Phosphataufnahme bei Ankistrodesmus braunii (1970)
    Springer
    Planta 93 (1970), S. 214-226 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The uptake of phosphate as influenced by sodium and potassium ions was investigated in the light and in the dark. It was found to be a function of the external phosphate concentration. At a low concentration (up to 10−5 mol/l) in the presence of Na+ phosphate is quickly absorbed and hence phosphate is the limiting factor for further labelling. In the presence of K+ phosphate uptake is constant over a long period. The enhancement of phosphate uptake by Na+ is also found when the external concentration of P is raised up to 10−4 mol/l. Then the gross uptake proceeds over six hours, with the greatest Na+-dependent increase occurring in the label of the TCA-insoluble phosphate fraction (Pu). The phosphate uptake is strongly dependent on the pH of the reaction mixture. In the presence of Na+ it is highest between pH 5.6 and 7. As the uptake in the presence of K+ parallels the dissociation curve of the dihydrogen form H2PO 4 − , the Na+-enhancement is optimal in the alkaline pH range (pH 8). On the basis of a comparison between the pH-dependence of phosphate uptake and the dependence of the uptake on the external phosphate concentration analysed by a method of enzyme kinetics, it is suggested that Ankistrodesmus metabolically transports H2PO 4 − but not HPO 4 = . Moreover, it is concluded from the absence of light stimulation and the weak inhibition of the uptake by DCMU or CCCP in the presence of K+ that at low P-concentrations the diffusion is limiting the uptake. Only at higher concentrations is an active phosphate uptake measured. Furthermore it is concluded that the observed Na+-stimulation of the 32P-labelling of the TCA-soluble and insoluble compounds inside the cell is indirect and depends only on the action of Na+ and K+ ions at the first transport site in the plasmalemma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00387642
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  • 8
    Electronic Resource
    Electronic Resource
    Phosphate uptake and its pH-dependence in halophytic and glycophytic algae and higher plants (1974)
    Springer
    Oecologia 17 (1974), S. 17-26 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Phosphate uptake in various organs of higher plants, i.e. Hordeum roots Avena coleoptiles, leaves of Elodea, and seedlings of the halophytes Cakile maritima, Cochlearia anglica, and Plantago maritima is optimal in the acidic pH range and is not stimulated by Na+ when tested in comparison to K+. In certain algae, i.e. the thermophilic blue-green alga Anacystis nidulans, the freshwater red alga Porphyridium aerugineum and the marine red alga Porphyridium cruentum, phosphate uptake is optimal in the alkaline pH range. In the red algae phosphate uptake is enhanced by Na+; in the marine species the increase is up to 100 times the rate in the presence of K+. It is suggested that the Na+-stimulated phosphate uptake has some phylogenetic and ecological significance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00345092
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  • 9
    Electronic Resource
    Electronic Resource
    Der Einfluß von Natrium- und Kalium-Ionen auf die Photophosphorylierung bei Ankistrodesmus braunii (1970)
    Springer
    Planta 92 (1970), S. 358-373 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary During short-time experiments (30 sec to 60 min) sodium ions stimulate the phosphate uptake and especially the 32P-labelling of the organic TCA-soluble phosphate compounds up to 1,500% (K+=100%). The labelling is maximally stimulated in the light and in the dark at concentrations of about 5×10-3 mol/l Na+ and at pH 8. Lithium ions stimulate 32P-labelling in a similar but less effective way. In comparison, in the presence of potassium ions the 32P-label decreases. It was investigated whether sodium ions specifically stimulate the ATP-synthesis or some reaction of the photosynthetic carbon reduction cycle or whether they only enhance the 32P-labelling of phosphorylated compounds. Separation by thin-layer chromatography of the MCF-soluble phosphate fraction showed that labelling of all compounds investigated was stimulated by Na+ to a similar extent. Experiments performed in red and far-red light (683 and 712 nm) under nitrogen and in the presence of various DCMU-concentrations, as well as in the presence of antimycin A and CCCP showed that Na+ exerts no specific influence either on the cyclic or on the non-cyclic photophosphorylation in vivo. ATP-dependent reactions such as 14CO2-fixation or glucose uptake are not influenced by Na+. Since Na+ does not change the size of phosphate pools in a different way from K+, there is no evidence for the assumption that the Na+-dependent increase in the 32P-labelling is due to its action on the chloroplast membrane in increasing its permeability to orthophosphate ions. This is supported by the lack of any effect of sodium plus phosphate ions on the CO2-fixation. Therefore the results give no evidence that sodium acts directly on phosphorus metabolism inside the cell. It is suggested that its action is localised at the phosphate-transporting site of the plasmalemma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385102
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  • 10
    Electronic Resource
    Electronic Resource
    Die pH-Abhängigkeit der Aufnahme von H2PO 4 - , SO 4 = , Na+ und K+ und ihre gegenseitige Beeinflussung bei Ankistrodesmus braunii (1973)
    Springer
    Planta 109 (1973), S. 161-176 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Ion uptake was studied using 32P, 35S, 22Na and 42K as tracers in synchronized cells of Ankistrodesmus, which were slightly starved with respect to the ions to be investigated. In the light and in the dark, phosphate uptake is maximal between pH 5.5 and 6.5. Whereas Na+ in comparison to K+ enhances phosphate uptake in the light (8 to 9-fold) and in the dark, Ca++ exerts only a slightly stimulatory effect. The stimulation of phosphate binding by Na+ occurs rapidly, even after less than 5 sec of incubation, and also in the presence of an equimolar concentration of K+. The pH-dependence of Na+-uptake in the light and in the dark is comparable to a dissociation curve: Na+-uptake increases with decreasing extracellular H+-concentration and is inversely proportional to phosphate uptake in the absence of Na+. The light:dark ratio of Na+-uptake at pH 8 amounts to 7:1. Mere adsorption of Na+ is similarly dependent on the pH. K+ strongly competes with Na+-uptake, even at pH 8. K+-uptake proceeds in a quite different manner from Na+-uptake and has an optimum at pH 7. Sulfate is taken up linearly in a biphasic process as a function of time; the pH-optimum lies between pH 7.5 and 8. K+ but not Na+ slightly enhances sulfate uptake. The Na+-enhancement of phosphate uptake can be related neither to a sodium-potassium exchange pump nor to a photosynthesis-dependent ion-exchange reaction. The results suggest that the uptake of phosphate, Na+ and K+, and the influence of alkali cations on phosphate uptake, but not sulfate uptake, are strongly dependent on fixed charges of the plasmalemma or even of the cell wall. These fixed charges may even prevent an active ion uptake.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00386124
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