The Fabrication of H+-Selective Liquid-Membrane Micro-electrodes for Use in Plant Cells

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Abstract
The hydrogen ion-sensitive liquid-membrane micro-electrode, as described by Amman, Lanter, Steiner, Schulthess, Shijo, and Simon (1981) has been developed further and made applicable for turgescent plant cells even with tough cell walls, by treatment with polyvinylchloride (PVC). Such an electrode is slower (t½=5–10 s) than the untreated electrode (t½=2–6 s), but displays 55–59 mV/pH-unit between pH 4·3 and 9·0, and is almost insensitive towards different buffers and K+. The electrodes are usable on more than one cell and have still good recalibration properties. Testing the electrodes on 11 different cell types of Riccia fluitans, Sinapis alba, Zea mays, Avena sativa, Kalanchöe daigremontiana, Lemna gibba and Chara corallina, we find the internal pH slightly alkaline (7·1–7·6) in ten cases (exception: old rhizoids of Riccia, pH1=4·8). From that we conclude that the pH-electrode measures in the cytosol. According to the different plant material, several procedures for internal pH-measurements are presented and supported by data: Application of cyanide and acetic acid causes internal acidification. Light-off transiently alkalinazes, light-on transiently acidifies the internal pH. The advantages and limitations of the method are critically discussed, and it is concluded that this electrode is a powerful tool in plant physiology.