Patch Clamp Studies on the Transport of Ions Across the Membrane of Barley Vacuoles
In photosynthesis of C3 plants such as wheat, spinach and barley, the main part of the fixed carbon is converted to sucrose (Giersch et al., 1980; Stitt et al., 1980). However, significant amounts of the assimilated carbon are also found in malate, which exhibits pronounced diurnal concentration (Gerhardt et al., 1986). In assimilating barley mesophyll protoplasts it could be shown that malate is rapidly transported in the vacuoles (Kaiser et al., 1982). In spinach leaves, the vacuolar malate concentration at the end of the day can increase up to 50 mM whereas the cytosolic malate concentration remains at about 5 mM (Gerhardt et al., 1986). This suggested that the malate transport into the vacuoles is an energy driven process. During the following night period malate is released into the cytosol where it presumably serves as a substrate for the mitochondrial respiration. In addition to malate, H+ and K+ ions also cross the vacuolar membrane in order to maintain electroneutrality and isoosmolarity between the cytosol and the vacuole. Using vacuoles isolated from barley mesophyll protoplasts we have recently shown that malate can be transported into the vacuoles against its concentration gradient (Martinoia et al., 1985). The driving force of the active transport is provided by an H+-translocating ATPase located in the vacuolar membrane (Martinoia et al., 1985). Like other H+-translocating ATPases, this ATPase can be inhibited by vanadate, olygomycin and azide but it is stimulated in the presence of anions (in particular chloride) and inhibited by nitrate.
KeywordsVacuolar Membrane Pump Current Single Channel Current Leaf Protoplast Patch Clamp Study
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- Gerhardt, R., Stitt, M., and Heldt, H. W., 1986, Plant Physiol. in press.Google Scholar
- Giersch, C. Heber, U., Kaiser, G., Walker, D. A., and Robinson, S. P., 1980, Intracellular metabolite gradients and flow of carbon during photosynthesis of leaf protoplasts, Arch. Biochem. Biophys., 205:246.Google Scholar
- Hamill, O. P., Marty, A., Neher, E., Sakmann, B., and Sigworth, F. J., 1981, Pfiigers Arch. Ges. Physiol. 39J: 85–100.Google Scholar
- Kaiser, G., Martinoia, E., and Wiemken, A., 1982, Rapid appearence of photosynthetic products in the vacuoles isolated from barley mesophyll protoplasts by a new fast method, Z. Pflanzenphysiol. 107: 103.Google Scholar
- Martinoia, E., Flügge, U. I., Kaiser, G., Heber, U., and Heldt, H. W., 1985, Energy-dependent uptake of malate into vacuoles isolated from barley mesophyll protoplasts, Biochim. Biophys. Acta 806:311.Google Scholar
- Stitt, M., McLilley, R. and Heldt, H. W., 1982, Adenine nucleotide levels in the cytosol, chloroplasts and mitochondria of wheat leaf protoplasts, Plant Physiol., 70: 971–977.Google Scholar
- Stitt, M., Wirtz, W., and Heldt, H. W., 1980, Metabolite levels during induction in the chloroplast and extra-chloroplast compartments of spinach protoplasts, Biochim. Biophys. Acta, 593:85–102.Google Scholar