The motive force of the migrating pseudoplasmodium of Dictyostelium discoideum under dark and light conditions.

As a contribution to the understanding of the mechanism of the collective motion of the cell mass in the migrating pseudoplasmodium its motive force has been determined. The measurements in the present paper were made by an original method using centrifugal force. The maximum value of the motive force of a migrating pseudoplasmodium in the dark was estimated as 0.6-1.6 dyn. This value is comparable to the motive force of protoplasmic streaming in Physarum polycephalum. In addition, the motive force in phototactic migration, which has not previously been estimated, was measured. Illumination from the front increased the motive force, whereas illumination from the back produced the opposite results. That is to say, illumination could directly influence the motive force. Furthermore, some interesting results were obtained by measuring the changes in the velocity of the pseudoplasmodia placed under four conditions (combinations of illuminated or non-illuminated, and parallel or antiparallel to the direction of the external force). These results suggest the necessity of taking into consideration the direct effect of light upon the motility of the cells in the migrating pseudoplasmodium.