Abstract
In most aquatic habitats, plants use bicarbonate as a carbon source of photosynthesis, and hydoxyl ions are extruded to the cell exterior, resulting in alkalization of the external medium. In characean cells, hydroxyl ions are extruded at fixed positions, forming so-called alkaline bands. Lucas (1976) studied the effect of external potassium on the bicarbonate incorporation. At 10 m M KCl, bicarbonate incorporation was severely inhibited in most cells. However, it was not inhibited in some cells. In the present study, we analyzed the effect of KCl on alkaline band formation. In most cells, the plasma membrane was suddenly depolarized in the presence of 10 mM KCl. In such cells, formation of alkaline band was severely inhibited. In some cells, however, the membrane remained polarized during the measurement. In such cells, alkaline bands were normally formed. It was concluded that the membrane potential is necessary for alkaline band formation
