The Formation of Alkaline and Acid Regions at the Surface of Chara corallina Cells

The magnitude of previously reported pH changes at the surfaceof Chara corallina cells has been measured with specially constructedpH electrodes. An experimental system was designed to reducethe dissipation of pH gradients by convection. When cells areilluminated their surfaces become partitioned into alkalineregions (pH 8.5–9.5) with sharp peaks and acid regions(pH about 5.5) which are more uniform. In the dark these regionsrapidly disappear and the pH of the cell surface becomes uniform(about pH 6.0). With cells initially free of any deposits ofCaCO₃, alkaline regions may appear temporarily, and may migratealong the cell surface. The presence of CaCO₃ stabilizes theregions. It is proposed that alkalinization results from HCO₃^–uptake, CO₂ fixation, and subsequent localized OH- efflux. Alkalinizationis prevented by photosynthetic inhibitors. The nature and magnitude of the HCO₃^–/OH- exchange processis discussed, and the possible role of H⁺ and OH- fluxes incontrolling the ionic and electrical properties of Characeancells is emphasized.