Light-induced electrical potential changes and motility in desmids.

Motility of the desmid Cosmarium cucumis depends on light: switching the light on induces a large fraction of previously immotile cells to start moving, and switching it off causes many motile cells to stop. Turning light on or off causes light-induced electrical potential changes which can be measured with internal microelectrodes. The electrical gradient within the cell is not correlated with the light gradient. Consequently, the cell cannot obtain information concerning the spatial distribution of the incident light, e.g. for phototactic orientation. However, light-induced potential changes could serve as signals for photokinesis, since switching the light on causes a transient increase and switching the light off a transient decrease in the electrical potential of the front half as compared to the rear half or the extracellular space.