Light-induced changes of bioelectric potential in Chara

Experiments were performed on light-induced changes of the resting potential in Chara under various conditions. In the dark-adapted cells, a slow increase in resting potential, by about 60 mv, appeared in a solution containing 0.5 mM KCl, 0.2 mM NaCl and 0.5 mM CaCl2. On the contrary, a rapid decrease preceded by a small, sharp rise in potential was produced when the cells became adapted to light. On the first illumination, the cell membrane resistance decreased in dark-adapted cells, but a slight increase was observed every time on subsequent illuminations. No parallel relation was found between the time course of the changes of resistance and the potential difference. During several illuminations, as well as during the short dark periods between them, cells lost their sensitivity to change in a potassium concentration. The time courses of photosynthetic oxygen evolution were not in accordance with those of changes in the potential. However, 10μM 3-(3,4-dichlorophenyl)-l, l-dimethylurea reversibly abolished both the oxygen evolution and the changes in potential. An enhancement of the photoelectric response was observed when bicarbonate ions were added in the external solution. On the other hand, the oxygen evolution was not affected by the bicarbonate ions. On the basis of these observations it was assumed that some assimilation products of photosynthesis were responsible for the photoelectric response.