Summary
The digestion of food in the heliozoonActinophrys sol is characterized by several distinct membrane events. Initially, extrusomes expand and fuse with each other and with the plasma membrane providing the membrane for the nascent food vacuole. During this process a—presumably lytic—material is secreted. After complete forming of the food vacuole a second type of vesicles fuses with it, whereupon usually lysis of the prey occurs. After denaturation and coagulation of the food, fluid is removed from the food vacuole. This process is accompanied by a high cytotic activity around the periphery of the food vacuole. Following this step, the perinuclear Golgi region shows an active appearance and numerous lysosomes fuse with the food vacuole. In consequence of this the food is degradated. The food vacuole shrinks continuously. Simultaneously vesicles filled with the digested material pinch off from the food vacuole, the content of which shows a more and more condensed mass of undigestible material. The undigestible residues are defecated eventually.
The process of digestion is accompanied by an increase in volume and number of electron lucent cytoplasmic vacuoles. These vacuoles gradually become filled with a filamentous material starting with the vacuoles in the cell periphery. As the digestion continues, the vacuolar contents become condensed successively. Synchroneously the vacuoles move towards the cell center. After completion of the digestion, the cytoplasmic vacuoles decrease in volume and number and do not show any longer electron dense contents.
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Linnenbach, M., Hausmann, K. & Patterson, D.J. Ultrastructural studies on the food vacuole cycle of a heliozoon (Feeding byActinophrys, III). Protoplasma 115, 43–51 (1983). https://doi.org/10.1007/BF01293579
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DOI: https://doi.org/10.1007/BF01293579