External pH Modifies the Intracellular pH and the Mode of Photosynthetic CO2-Assimilation in Photoautotrophic Cell Suspension Cultures of Chenopodium rubrum L. |
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Authors: | W. Hü semann,R. Callies,D. Leibfritz |
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Abstract: | Photoautotrophic cell supension cultures of C. rubrum exhibit a C3-type of photosynthesis. Yet, up to 20% of total CO2-fixation is directly incorporated into malate and aspartate during short-term photosynthesis. The rate of 14C-labeling of malate and aspartate was doubled if the pH of the medium of the cells was increased from the normal value of 4.5 to 6.0 or 7.0. In vivo 31P-NMR spectroscopy demonstrated that an increase in the external pH from 4.5 to 6.3 increased the cytosolic pH by 0.3 units and the vacuolar pH by about 1.3 units. Possible mechanisms for the effect of extracellular pH on intracellular pH and PEP-carboxylase-dependent carboxylation reactions are discussed. |
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Keywords: | Photoautotrophic cell cultures external pH intracellular pH 31P-NMR spectroscopy CO2-assimilation malate formation |
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