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SYNERESIS IN AMEBOID MOVEMENT: ITS LOCALIZATION BY INTERFERENCE MICROSCOPY AND ITS SIGNIFICANCE

R. Allen,R. R. Cowden

Published 1962 in Journal of Cell Biology

ABSTRACT

The periodic appearance of a hyaline cap at the front of advancing pseudopodia is an almost universal accompaniment of movement in ameboid cells. The fluid of the hyaline cap cannot be a simple filtrate of the ground substance pressed through the "plasmagel sheet" as Mast (11, 12) believed, because the dry mass of this fluid is less than half that of the ground substance of the rest of the cell (5). Neither can this fluid be derived from the environment, for the turnover rate of water is orders of magnitude too slow (10). The low dry mass of the hyaline cap fluid, therefore , indicates that it is produced by syneresis accompanying the contraction of a gelated region somewhere within the cell. The site of the contraction which serves as the motive force for ameboid movement has never been clearly established. The ectoplasmic contraction theory (or tail contraction theory) (7, 8, 11, 14) would lead one to predict that the origin of the hyaline cap fluid would be the contracting tail ectoplasm (7). This possibility seemed to receive strong support from the gradient of optical path difference in flattened amebae demonstrated by Allen and Roslansky (5). These data, in fact, suggested that contraction of the tail ectoplasm released a "tide" of syncretic fluid which was pressed forward, its anterior margin visible as the hyaline cap. However, Allen and Roslansky pointed out several aspects of ameboid movement which were not in good agreement with the theory. Recently, one of us (2, 3) has proposed a new theory which is compatible with the various be-havioral aspects of ameboid movement and with the limited amount of experimental data available. The new theory postulates a contraction at the front of each advancing pseudopod as the motive force for movement. This front contraction theory rests on the same two basic assumptions as the tail contraction theory: first, that the cytoplasm of ameboid cells can exist in at least two states, contracted and extended, and, second, that the driving contraction is propagated along the cytoplasm, as it is in muscle. According to the new theory, the contraction occurs in the endo-plasm as the latter splits and becomes everted to form the ectoplasmic tube. The region just posterior to the hyaline cap where this is postulated to occur has been called the "fountain zone" (2, 3). The front contraction theory (or fountain zone contraction theory) demands that …

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