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  • 1
    ISSN: 1432-1939
    Schlagwort(e): CAM-epiphyte ; Light acclimation ; Photoinhibition ; Growth
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Kalanchoë uniflora was grown in the glasshouse with and without shading. Chlorophyll content, area/FW ratio and specific leaf area were higher in leaves of shaded as compared to unshaded plants. Light saturation curves and continuous gas exchange measurements showed that the apparent quantum yield and the light-saturated photosynthetic rate were higher in shaded plants. Shaded plants had lower “mesophyll resistances” than unshaded plants, indicating that the different photosynthetic capacities reflected different contents of ribulose biphosphate carboxylase-oxygenase. Highlight treatment of plants grown in the shade resulted in a decreased photosynthetic efficiency, showing that these plants were sensitive to photoinhibition. However, dry matter production was higher in unshaded than in shaded plants. Obviously the difference in irradiance between the two growth regimes did more than offset the differences in photosynthetic efficiency. Applying additional nutrients did not alter the effects of high PFDs. The results are discussed in respect to photosynthetic performence and plant distribution in the epiphytic habitat.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    ISSN: 1432-2048
    Schlagwort(e): ATP ; Citrate transport ; Hevea ; Proton pump ; Vacuole
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The relationship between the electrochemical proton gradient, Δ μH+ − , and citrate transport has been studied in tonoplast vesicles from Hevea brasiliensis (the rubber tree). Vesicles were generated from lyophilized samples of fresh vacuoles obtained from the latex sap. Methylamine was used to measure intravesicular pH and lipophilic ions to determine the electrical potential difference (ΔΨ) across the tonoplast. When incubated at pH 7.5 in the absence of ATP, the tonoplast vesicles showed a ΔpH of 0.6 units (interior acid) and a ΔΨ of about-100 mV (interior negative). This potential is thought to be made up of contributions from an H+ diffusion potential, diffusion potentials from other cations and a Donnan potential arising from the presence of internal citrate. In the presence of 5 mol m-3 MgATP the ΔpH was increased to about 1.0 unit and the ΔΨ to about-10 mV. Under these conditions the proton-motive force (Δ p Δ μH+ − /F) became positive and reached +50 mV. These effects were specific to MgATP (ADP and Mg2+ having no significant effect) and were prevented by the protonophore p-trifluoromethoxycarbonylcyanidephenylhydrazone (FCCP). Citrate uptake by the vesicles was markedly stimulated by MgATP; ADP and Mg2+ again had no effect. Nigericin greatly increased ΔpH and this was associated with a large increase in citrate accumulation. The results indicate that the vesicle membrane possesses a functional H+-translocating ATPase. The Δ μH+ − generated by this ATPase can be used to drive citrate uptake into the vesicles. The properties of the tonoplast vesicles are compared with those of the fresh latex vacuoles.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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