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  • 1
    Electronic Resource
    Electronic Resource
    New approach of monitoring changes in chlorophyll a fluorescence of single guard cells and protoplasts in response to physiological stimuli (1999)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 22 (1999), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A new type of microfluorometer was applied to assess photosynthesis at the single-cell level by chlorophyll fluorescence using the saturation pulse method. A microscopy–pulse amplitude modulation (PAM) chlorophyll fluorometer was combined with a Zeiss Axiovert 25 inverted epifluorescence microscope for high-resolution measurements on single mesophyll and guard cells and the respective protoplasts. Available information includes effective quantum yield of photosystem II, relative electron transport rate and energization of the thylakoid membrane due to the transthylakoidal proton gradient. Dark–light induction curves of guard cell (GCPs) and mesophyll cell protoplasts (MCPs) displayed very similar characteristics, indicating similar functional organization of thylakoid membranes in both types of chloroplasts. Light response curves, however, revealed much earlier saturation of photosynthetic electron flow in GCPs than in MCPs. Under anaerobiosis, photosynthetic electron flow and membrane energization were severely suppressed. A similar effect was observed in guard cells when epidermal peels were incubated with the fungal toxin fusicoccin which activates the plasma membrane H+-ATPase and causes irreversible opening of stomata. The drop in electron transport rate was prevented by blocking ATP consumption of the H+ pump or by glucose addition. These results show that chlorophyll fluorescence quenching analysis allows profound insights into stomatal physiology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1999.00475.x
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  • 2
    Electronic Resource
    Electronic Resource
    Book reviews (1995)
    Springer
    Journal for general philosophy of science 26 (1995), S. 345-363 
    Details
    ISSN: 1572-8587
    Source: Springer Online Journal Archives 1860-2000
    Topics: Philosophy , Nature of Science, Research, Systems of Higher Education, Museum Science
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00766734
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of chlorine and other halogens by activation with photons and neutrons (1998)
    Springer
    Fresenius' journal of analytical chemistry 362 (1998), S. 382-386 
    Details
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The analysis of halogens in various matrices is described. Activation analysis with mainly high energy bremsstrahlung (PAA) and pile neutrons (NAA) was applied. In the case of chlorine, fast procedures were worked out requiring not more than 100 min for one determination. The particular problems of fluorine analysis are discussed. The described techniques were applied for the following cases: Determination of total chlorine resp. bromine in oil samples; determination of chlorine in wood, glasses and TiN powders; determination of iodine in ZnSe single crystals using instrumental photoactivation.The limits of detection are: (interference-free in μg/g) F: 0.03/–; Cl: 0.1/0.05; Br: 0.04/0.003 and I: 0.1/0.01 using PAA/NAA. Activation analysis, being independent upon the chemical status of the analyte and usually less affected by blank problems has been found to be a useful complement to conventional chemical analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002160051089
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  • 4
    Electronic Resource
    Electronic Resource
    Limited polymorphism in the first domain of the rat MHC class II RT1-D molecule (1998)
    Springer
    Immunogenetics 48 (1998), S. 344-349 
    Details
    ISSN: 1432-1211
    Keywords: Key words Genes ; MHC class II ; Histocompatibility antigens ; Polymorphism (genetics) ; Rats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002510050442
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  • 5
    Electronic Resource
    Electronic Resource
    Anions modify the response of guard-cell anion channels to auxin (1995)
    Springer
    Planta 197 (1995), S. 546-552 
    Details
    ISSN: 1432-2048
    Keywords: Auxin ; Anion channel (GCAC1) ; Guard cell ; Malate ; Vicia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The anion channel in the guard-cell plasma membrane of Vicia faba, GCAC1, possesses recognition sites for the plant growth hormone auxin at the extracellular mouth of the channel (Marten et al. 1991, Nature 353:759-762). Using the patch-clamp technique we could demonstrate that auxins induced a shift of the voltage dependence of the anion channel to hyperpolarized potentials; the shift was attenuated during an increase in the extracellular chloride concentration, indicating that chloride shields the hormone-binding site. The auxin-induced shift was concentration-dependent, characterized by a Michaelis-Menten type of behaviour with a half saturation constant (K m) of about 10 μM naphthalene-1-acetic acid (1-NAA) in the presence of 2 mM Cl− and 12 μM in 80 mM Cl−. In the presence of malate, another gating modulator of GCAC1, auxins were less effective, indicating that both ligands compete for common sites. Inactive auxins with respect to stomatal opening or stimulation of the plasma membrane H+-ATPase, such as 2-NAA, modulated the activation threshold and kinetics of GCAC1 similar to the active form 1-NAA. At a concentration of 100 μM 2-NAA the peak-current potential shifted by about 30 mV more negative.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00196677
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  • 6
    Electronic Resource
    Electronic Resource
    Inward rectifier potassium channels in plants differ from their animal counterparts in response to voltage and channel modulators (1995)
    Springer
    European biophysics journal 24 (1995), S. 107-115 
    Details
    ISSN: 1432-1017
    Keywords: Potassium channel ; KAT1 ; Voltage dependence ; Cesium block ; pH dependence ; Kinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract We have investigated the electrophysiological basis of potassium inward rectification of the KAT1 gene product from Arabidopsis thaliana expressed in Xenopus oocytes and of functionally related K+ channels in the plasma membrane of guard and root cells from Vicia faba and Zea mays. The whole-cell currents passed by these channels activate, following steps to membrane potentials more negative than −100 mV, with half activation times of tens of milliseconds. This voltage dependence was unaffected by the removal of cytoplasmic magnesium. Consequently, unlike inward rectifier channels of animals, inward rectification of plant potassium channels is an intrinsic property of the channel protein itself. We also found that the activation kinetics of KAT1 were modulated by external pH. Decreasing the pH in the range 8.5 to 4.5 hastened activation and shifted the steady state activation curve by 19 mV per pH unit. This indicates that the activity of these K+ channels and the activity of the plasma membrane H+-ATPase may not only be coordinated by membrane potential but also by pH. The instantaneous current-voltage relationship, on the other hand, did not depend on pH, indicating that H+ do not block the channel. In addition to sensitivity towards protons, the channels showed a high affinity voltage dependent block in the presence of cesium, but were less sensitive to barium. Recordings from membrane patches of KAT1 injected oocytes in symmetric, Mg2+-free, 100 mM-K+, solutions allowed measurements of the current-voltage relation of single open KAT1 channels with a unitary conductance of 5 pS. We conclude that the inward rectification of the currents mediated by the KAT1 gene product, or the related endogenous channels of plant cells, results from voltage-modulated structural changes within the channel proteins. The voltage-sensing or the gating-structures appear to interact with a titratable acidic residue exposed to the extracellular medium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00211406
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  • 7
    Electronic Resource
    Electronic Resource
    Mapping of H2-M homolog and MOG genes in the rat MHC (1995)
    Springer
    Immunogenetics 42 (1995), S. 418-421 
    Details
    ISSN: 1432-1211
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00179405
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  • 8
    Electronic Resource
    Electronic Resource
    Pronounced differences between the native K+ channels and KAT1 and KST1 α-subunit homomers of guard cells (1999)
    Springer
    Planta 207 (1999), S. 370-376 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Arabidopsis ; Guard cell ; Heterologous expression (K+-channel subunits) ; K+channel ; (KAT1 ; KST1 subunits) ; Solanum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Stomatal opening is the result of K+-salt accumulation in guard cells. Potassium uptake in these motor cells is mediated by voltage-dependent, K+-selective ion channels. Here we compare the in-vitro properties of two guard-cell K+-channel α-subunits from Arabidopsis thaliana (L.) Heynh. (KAT1) and Solanum tuberosum L. (KST1) after heterologous expression with the respective K+-transport characteristics in their mother cell. The KAT1 and KST1 subunits when expressed in Xenopus oocytes shared the basic features of the K+-uptake channels in the corresponding guard cells, including voltage dependence and single-channel conductance. Besides these similarities, the electrophysiological comparison of K+ channels in the homologous and the heterologous expression systems revealed pronounced differences with respect to modulation and block by extracellular cations. In the presence of 1 mM Cs+, 50% of the guard-cell K+-uptake channels (GCKC1in) in A. thaliana and S. tuberosum, were inhibited upon hyperpolarization to −90 mV. For a similar effect on KAT1 and KST1 in oocytes, voltages as negative as −155 mV were required. In contrast, compared to the K+ channels in vivo the functional α-subunit homomers almost lacked a voltage-dependent block by extracellular Ca2+. Similar to the block by Cs+ and Ca2+, the acid activation of the α-homomers was less pronounced in oocytes. Upon acidification the voltage-dependence shifted by 82 and 90 mV for GCKCLin in A. thaliana and S. tuberosum, respectively, but only by 25 mV for KAT1 and KST1. From the differences in K+-channel modulation in vivo and after heterologous expression we conclude that the properties of functional guard-cell K+-uptake channels result either from the heterometric assembly of different α-subunits or evolve from cell-type-specific posttranslational modification.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050494
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  • 9
    Electronic Resource
    Electronic Resource
    Cation sensitivity and kinetics of guard-cell potassium channels differ among species (1998)
    Springer
    Planta 205 (1998), S. 277-287 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Cation sensitivity ; Guard cell ; K+ channel ; Nicotiana ; Solanum ; Vicia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. in ward rectifying g uard c ell K + c hannel, GCKC1in, from three major crop plants Solanum tuberosum L., Nicotiana tabacum L., and Vicia faba L. Selecting guard cells for our analyses we aimed to test whether K+ channels of the same cell type differ among species. The channels shared basic features including voltage-dependence, selectivity and single-channel conductance. They activated at hyperpolarization (V 1/2 ≈ −164 mV) with single channels of 7 pS underlying the whole-cell current. The channel density in S. tuberosum was higher than in V. faba and N. tabacum while the activation and deactivation kinetics were faster in the latter two species. Among different monovalent cations the K+ channels discriminated strongly against Na+, Li+, and Cs+. The sensitivity to Cs+ was similar for the three species. Extracellular Ca2+ blocked the V.␣faba K+ channel at concentrations ≥1 mM but only affected its functional homologs in S. tuberosum and N.␣tabacum at higher concentrations and more-negative membrane potentials. Like the differences in Ca2+-sensitivity, protoplasts from the three species differed remarkably in their response towards extracellular pH changes. Whereas protons neither altered the open probability nor the kinetic parameters of the V. faba GCKC1in, in S. tuberosum and N. tabacum this cation affected the voltage-dependent properties strongly. An increase in proton concentration from pH 8.5 to 4.5 shifted the potential of half-maximal open probability to less-negative values with a maximum effect around pH 6.2. The pH modulation of the K+ channels could be described assuming a two-state model where the open and closed channel can be protonated. The observed differences in cation-sensitivity and voltage-dependent kinetics between K+ channels reflect the diversification of guard-cell channels that may contribute to species-specific variations in the control of stomatal aperture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050322
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  • 10
    Electronic Resource
    Electronic Resource
    Susceptibility of the guard-cell K+-uptake channel KST1 to Zn2+ requires histidine residues in the S3-S4 linker and in the channel pore (1999)
    Springer
    Planta 209 (1999), S. 543-546 
    Details
    ISSN: 1432-2048
    Keywords: Key words: KST1 ; Mutagenesis ; Potassium channel ; Solanum ; Stomata ; Zn2+
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract.  Potassium channels are inhibited by several mono- and divalent cations. To identify sites involved in the interaction between K+ channels and cationic effectors, we expressed the potato (Solanum tuberosum L.) guard-cell K+-uptake channel KST1 in Xenopus oocytes. This channel was reversibly blocked by extracellular Zn2+ in the micromolar range. In the presence of this heavy metal, steady-state currents were reduced in a pH-dependent but voltage-independent manner. Since Zn2+-inhibition was less effective at elevated external proton concentrations, we generated alanine mutants with respect to both extracellular histidines in KST1. Whereas substitution of the pore histidine H271 resulted in a reduced blockade by Zn2+, the channel mutant KST1-H160A in the S3-S4 linker lost most of its Zn2+ sensitivity. Since both histidines alter the susceptibility of KST1 to Zn2+, the block may predominantly result from these two sites. We thus conclude that the S3-S4 linker is involved in the formation of the outer pore.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050759
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