H+Transport across the Plasmalemma and Tonoplast ofNitellopsis obtusaduring Excitation

Abstract

Measurements of intra- and extracellular pH during the excitation of Nitellopsis obtusa were carried out with antimony microelectrodes at conditions of dark adaptation and of continuous illumination. The pH of the vacuolar sap of both dark-adapted and illuminated cells increased during cell excitation by 0-1-0-15 units. H+ ions which had entered the cytoplasm during excitation in dark-adapted cells were extruded back into the vacuole across the tonoplast. After cell excitation in the light H+ ions were extruded from the cytoplasm also into the external medium probably across the light-stimulated active H+-channels. Protoplasmic streaming ceased during excitation in the dark for 1-3 min, and during excitation in the light—for 5-20 s.