Motive force of the migrating pseudoplasmodium of the cellular slime mould Dictyostelium discoideum.

Motive forces of migrating pseudoplasmodia (slugs) of Dictyostelium discoideum were determined by application of a double-chamber method. The motive force of a whole slug was proportional to its volume, the value per unit volume being 5.85 x 10(-6) dyne/cm3 (58.5 N cm-3). The motive force was independent of temperature (13.5--26 degrees C) and decreased during prolonged migration. Motive force per unit volume of an anterior isolate of a slug was much larger than that of a posterior isolate, their weighted mean being approximately equal to that of a whole slug. These results agree well with the predictions previously made using a model based on analyses of migrating velocities of slugs. The motive force per unit volume of either isolate was soon regulated to reach the normal value of an intact slug after several hours of isolation, concurrently with conversion of cell types between prestalk and prespore cells. The possibility that motive force of each cell is determined by its cell type is discussed in relation to cell sorting.