Andrzej Grebecki

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Behaviour of the membrane and contractile system was directly recorded in the advancing and retracting frontal zones of spontaneously locomoting or stimulated amoebae. The advancing pseudopodial tips alternately slow down and accelerate. In the slowing phase the frontal hyaline caps are flat and compressed by countercontraction of the cortical actin network(More)
The uroids, the posterior, middle and anterior segments of the intermediate body regions, and the frontal zones of Amoeba proteus were exposed, separately or in different combinations, to local increases or decreases of light intensity. In general, an increase of luminosity promotes contraction, and its decrease induces relaxation in any body region of(More)
Amoeba proteus cells, strains A and C t , with well pronounced motor polarity (the polytactic and orthotactic forms) develop dense coats of discrete minipodia which anchor them to the glass substratum. The scanning electron microscopy demonstrates that minipodia are surface microprotrusions about 0.5 μm thick and up to 8 μm long, covering mainly the(More)
The heat-pretreated amoebae (hyalospheres) are well suited cell models to study several manifestations of endocytosis: invagination of initial funnels, formation of pinocytotic channels, their activity and disintegration, production of microand macroendosomes directly from the surface membrane. All these phenomena are rhythmically reproduced (with periods(More)
Floating heterotactic cells ofAmoeba proteus were sedimented on untreated glass surfaces and on modified substrata, differing in their wettability and surface potential. About 95% of the amoebae readhere to the glass within 12 min and recover locomotive (polytactic) morphology within 13 min. The rate of locomotion resumption does not change significantly on(More)
Polytactic cells of Amoeba proteus were exposed to localized photic stimulation. When a pseudopodium is stimulated to advance, by shading it, other pseudopodia are retracted. Activation of the shaded front is the primary response, and contraction of other fronts the secondary one. When a pseudopodium is inhibited by illuminating its frontal segment, or when(More)
Before the furrow formation the non-polar general contraction resulting in cell de-adhesion and spherulation, and the following relaxation leading to re-adhesion, flattening and spreading, are both necessary prerequisites of a successful cytokinesis in A. proteus. The bipartition begins by sudden generation of two divergent cytoplasmic streamings at the(More)
The enucleated specimens of Amoeba proteus, the anucleate fragments, and the polynucleate individuals which all are capable of cortical contraction but not of locomotion, may be reactivated by the light-shade difference established across their body. Individual cells or fragments migrate toward the shade. The motory polarity and coordinated movement(More)
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(More)