Proton-Motive Force and H+/Amino-Acid Antiport at the Tonoplast of Riccia Fluitans Rhizoid Cells, Revealed by Direct Probing with the pH-Sensitive Microelectrode
The electrical properties of H+-amino-acid symport located at the plasmalemma of the freshwater liverwort Riccia fluitans has already been well characterized and described (Felle, 1981, 1983 and 1984; Johannes and Felle, 1985). Tracer compartment analysis proved fast and high accumulation of all amino-acids tested so far, including the nonmetabolizable amino-isobutyric acid (Aib) within the vacuole. It was desirable therefore, to carry out crucial tests, in order to clear up the mode of action of amino-acid transport across the tonoplast of this plant. It is generally assumed that a small electrical potential difference (positive inside the vacuole) and a large pH-gradient exist across tonoplast membranes. The recently developed turgor-resistent pH microelectrodes (Bertl and Felle, 1985; Felle and Bertl, 1986) seemed most promising (a) to measure the proton-motive force directly, and (b) to find out, whether amino-acids are transported along the proton-motive force or possibly in an electrically silent manner.
KeywordsTonoplast Membrane Membrane Potential Difference Difference Trace Rhizoid Cell Electrogenic Proton Pump
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