Relative motion inAmoeba proteus in respect to the adhesion sites. I. Behavior of monotactic forms and the mechanism of fountain phenomenon

Summary The unbranched ectoplasmic cylinder of monotacticA. proteus is always retracted toward the cell-substrate attachment sites. The retraction velocity increases from the adhesion sites toward any free distal body end in a linear way, which indicates the uniform contractility of the whole cylinder. Therefore, in the cells frontally attached all the ectoplasm moves forward, and in those adhering by the tail the whole ectoplasmic tube moves backward producing the full fountain phenomenon. With cell attachment at the middle body regions, which is most typical for normal locomotion, the whole ectoplasm is centripetally retracted from both body poles toward the adhesion zone, producing then the tail retraction in the posterior and incomplete fountain in the anterior body part. In unattached amoebae the whole peripheral tube is retracted toward its geometrical centre which coincides with its posterior closed end, producing therefore also a full fountain. It is generalized that the fountain arises always between an unattached front and the nearest attachment point behind its manifestation zone. The photographic records of movement and longitudinal velocity profiles of ectoplasmic retraction are identical on both sides of the attachment points, suggesting the same mechanism for the fountain movement as for the tail withdrawal. It is concluded therefore that not the axial endoplasmic arm of the fountain is active, but its peripheral arm built of the ectoplasm.All elements complicating the cell contour, as the constriction rings and ephemeral lateral pseudopodia, do not change their position in respect to the ectoplasmic material, but move together with it in respect to the substrate, i.e., the cytoskeleton moves as a whole. Loose glass rods attached by adhesion to cell surface also precisely follow the cytoskeleton movements, being transported toward the main locomotory adhesion zone established on the firm substrate, although the cell membrane as such behaves differently. It suggests a direct connection between the adhesion sites and the cytoskeleton.Study supported by Research Project II. 1 of the Polish Academy of Science.I dedicate this paper to the memory of Reginald J. Goldacre, deceased in December 1983, who twenty years ago introduced me to the study of amoebae.