Light-induced changes of bioelectric potential in Chara

Experiments were performed on light-induced changes of the restingpotential in Chara under various conditions. In the dark-adaptedcells, a slow increase in resting potential, by about 60 mv,appeared in a solution containing 0.5 mM KCl, 0.2 mM NaCl and0.5 mM CaCl₂. On the contrary, a rapid decrease preceded bya small, sharp rise in potential was produced when the cellsbecame adapted to light. On the first illumination, the cellmembrane resistance decreased in dark-adapted cells, but a slightincrease was observed every time on subsequent illuminations.No parallel relation was found between the time course of thechanges of resistance and the potential difference. During severalilluminations, as well as during the short dark periods betweenthem, cells lost their sensitivity to change in a potassiumconcentration. The time courses of photosynthetic oxygen evolutionwere not in accordance with those of changes in the potential.However, 10µM 3-(3,4-dichlorophenyl)-l, l-dimethylureareversibly abolished both the oxygen evolution and the changesin potential. An enhancement of the photoelectric response wasobserved when bicarbonate ions were added in the external solution.On the other hand, the oxygen evolution was not affected bythe bicarbonate ions. On the basis of these observations itwas assumed that some assimilation products of photosynthesiswere responsible for the photoelectric response. (Received February 13, 1968; )