Light-induced changes of cytosolic pH in Eremosphaera viridis: recordings and kinetic analysis

Abstract

Short-term light-induced pH changes were measured by means of pH-selective microelectrodes in the unicellular green alga Eremosphaera viridis. Cytosolic pH changes were always transient and reversible within 1–3 min. Taking into account the low-pass filtering by the experimental set-up, the light-dependent cytosolic pH changes could be described by a sum of two exponential functions. By mathematical analysis it is demonstrated that the transient nature of light-dependent pH changes was due to a consecutive pH-stat regulation and not to a parallel light-triggered reaction. The short-term pH regulation depended linearly on the pH-deviation with no indication of a feedback control loop. Vacuolar light-dependent pH changes were measured to investigate further which pH-stat mechanisms are responsible for the back regulation of the light-dependent cytosolic pH changes. Vacuolar pH changes were too small to explain the recovery of the cytosolic pH after darkening or illumination by H+ fluxes across the tonoplast.