Evidence for an action of fusicoccin on the vacuolar pH of acer pseudoplatanus cells in suspension culture

Regulation of Cytoplasmic and Vacuolar pH in Maize Root Tips under Different Experimental Conditions

“…Although Kurkdjian et al (10) recently reported evidence that vacuolar pH in sycamore cells increases after more than I h of fusicoccin-induced H+ extrusion, present results confirm our earlier findings (19) that, at least for the first 2 h, neither vacuolar nor cytoplasmic pH increases significantly during rapid H+ extrusion by maize root tip cells. As previously noted (19), this seems to rule out the conventional 'biochemical pH-stat' explanation of pH regulation (22) according to which H+ extrusion should cause an increase in cytoplasmic pH which would stimulate organic acid production, compensating for the H+ efflux and preventing further increase in intracellular pH.…”

“…As previously noted (19), this seems to rule out the conventional 'biochemical pH-stat' explanation of pH regulation (22) according to which H+ extrusion should cause an increase in cytoplasmic pH which would stimulate organic acid production, compensating for the H+ efflux and preventing further increase in intracellular pH. The cytoplasmic pH does not increase even transiently, as indicated by NMR spectra recorded during the first 10 (Fig. 2).…”

“…The most widely used method, using the weik acid ['4C]5,5,dimethyloxazolidine-2,4-dione (7,15,16,24), is indirect and fraught with complications (e.g. Kurkdjian et al [7][8][9][10]). Other methods of intracellular pH measurement, such as those using dyes, microelectrodes (22), and methylamine (9), have not been successfully applied to the cytoplasm of higher plant cells.…”

“…Here, we extend these studies by an improved technique involving perfusion of the tissue within the NMR spectrometer, permitting us to obtain adequate NMR spectra within 10 min and to monitor the intracellular pH of maize root tips over periods of more than 12 h, during a sequence of treatments.…”

Stimulation of Weak Acid Uptake and Increase in Cell Sap pH as Evidence for Fusicoccin- and K+-Induced Cytosol Alkalinization

“…The segments were then incubated in 10 ml of solution containing 0.5 mm CaSO4, 5 31) and can also be applied to the evaluation of the pH of 'bulk cytoplasm' (cytoplasmic organelles included) provided it is assumed that: (a) the pK of the weak acid is known, and is the same in all compartments; (b) only the uncharged acid form can passively diffuse across the cell membranes, so that at equilibration the concentration of the uncharged form of the acid is the same in all compartments, while that of the ionized form in each compartment is determined by the local pH; and (c) the metabolization of the weak acid is negligible. Then, 'bulk cytoplasmic' pH (pHc,,) can be calculated by the following equation, derived from that of Henderson-Hasselbalch (14,31):…”