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

The hydrogen ion-sensitive liquid-membrane micro-electrode,as described by Amman, Lanter, Steiner, Schulthess, Shijo, andSimon (1981) has been developed further and made applicablefor turgescent plant cells even with tough cell walls, by treatmentwith polyvinylchloride (PVC). Such an electrode is slower (t=5–10s) than the untreated electrode (t=2–6 s), but displays55–59 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 stillgood recalibration properties. Testing the electrodes on 11different cell types of Riccia fluitans, Sinapis alba, Zea mays,Avena sativa, Kalanchöe daigremontiana, Lemna gibba andChara 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 thecytosol. According to the different plant material, severalprocedures for internal pH-measurements are presented and supportedby data: Application of cyanide and acetic acid causes internalacidification. Light-off transiently alkalinazes, light-on transientlyacidifies the internal pH. The advantages and limitations ofthe method are critically discussed, and it is concluded thatthis electrode is a powerful tool in plant physiology. Key words: Internal pH, pH-sensitive micro-electrode     

Cytoplasmic pH of Root Hair Cells of Sinapis alba Recorded by a pH-sensitive Micro-electrode. Does Fusicoccin Stimulate the Proton Pump by Cytoplasmic Acidification?

Bertl, A. and Felle, H. 1985. Cytoplasmic pH of root hair cellsof Sinapsis alba recorded by a pH-sensitive micro-electrode.Does fusicoccin stimulate the proton pump by cytoplasmic acidification?—J. exp. Bot. 36: 1142–1149. pH-sensitive micro-electrodes, filled with ion-exchanger resinhave been fabricated with a turgorinsensitive tip and have beenapplied to test the intracellular pH and changes thereof inroot hair cells of Sinapis alba. (1) The cytoplasmic pH of Sinapisroot hairs was determined to be 7.3 ±0.2 (at neutralexternal pH). (2) 10 mol m^–3 sodium azide depolarizesthe membrane potential by about 100 mV and acidifies the cytoplasmby 0.8 pH-units. (3) The change from 1.0 mol m^–3 to 10mol m^–3 external potassium causes a depolarization ofabout 45 mV, but no change in internal pH. (4) At an externalpH of 5.0, sodium acetate hyperpolarizes the plasmalemma byabout 60 mV and acidifies the cytoplasmic pH by 0.2 to 0.3 units.(5) 2.0 mmol m^–3 fusicoccin (FC) hyperpolarizes the plasmalemmaby 20–25 mV, acidifies the cytoplasm by 0.1 to 0.2 pH-units,and acidifies the external medium by about 0–3 pH-units.It is concluded that cytoplasmic acidification stimulates theelectrogenic proton pump in Sinapis root hairs, and it is suggestedthat the FC-induced effects, viz. hyperpolarization and externalacidification, can also be interpreted in this way. Key words: —Cytoplasmic pH, pH-sensitive micro-electrode, fusicoccin