Relative motion inAmoeba proteus in respect to the adhesion sites

Summary

The whole ectoplasmic layer of polytactic and heterotactic forms ofA. proteus behaves as self-contractile structure. Depending on the configuration of cell body and on the cell-to-substrate attachment conditions it continuously retracts from each distal cell projection toward its centre and/or from each free body end toward the actual adhesion sites. As in the monotactic forms, it leads to the withdrawal of the tail region behind the retraction center and may result in the fountain movement in front of it. In the long unattached pseudopodia of heterotactic forms the ectoplasm is retracted in the fountain form, with the velocity linearly increasing from the basis of pseudopodium up to its tip. In polytactic cells the fountain is often absent, if the advancing fronts immediately adhere to the substrate. When they develop in unattached condition, or are experimentally obliged to detach, the ectoplasmic cylinders of frontal pseudopodia are retracted backwards. On the substrates which do not offer firm points of support the cell periphery moves back as a whole,i.e., the principal ectoplasmic cylinder retracts together with the cylinders of lateral pseudopodia, and the direction and speed of movement in any spot is the resultant of forces produced by all other segments. The retraction of ectoplasmic gel layer is independent of the endoplasmic flow in such extent that a pseudopodium may be withdrawn as a whole in spite of the endoplasm streaming directed forwards in its interior. On the cell surface the particles attached by adhesion (glass rods) strictly follow the movements of the internal ectoplasmic structures, whereas the unattached particles flow forward in the direction of endoplasm streaming.