Summary
The suctorian feeding organelles, the tentacles, display a peculiar tube-like microtubule array through which the food is ingested. The basic pattern of this inner tentacle tube consists of an outer cylinder of single microtubules and an inner cylinder of microtubule ribbons. The present observations on number, distribution and arrangement of microtubules in the tentacle arms of Dendrocometes paradoxus strongly suggest that the distal area of the tentacle plays the most important role in the mechanism of food intake and the transport of the ingested material down the tentacle. Near the tip of the tentacle—which in most species bears a knob-like broadening—the highest number of microtubules is observed. Here the single microtubules of the outer cylinder are attached to a fibrillar material, forming a manchette-like structure which keeps the inner microtubule ribbons in position. It is only at this level that each microtubule of these ribbons bears a single projection, which probably represents the morphological link to the ingested material. Based on the observations in Dendrocometes and all data available concerning the fine structure of other Suctoria, a general model of the function of the tentacle is developed, interpreting food intake as a “grasp- and swallow” rather than a suction mechanism. It is suggested that a sliding back and forth of the microtubule ribbons coupled with a cyclic bridging- and release mechanism between the microtubule projections and the membrane (that comes down with the food) is the most likely explanation for the peculiar feeding mechanism. The mechanical properties of the proposed model as well as other microtubule transport systems, e.g. saltatory movement of organelles in the heliozoan axopod, axoplasmic transport, and chromosome movement are discussed to some extent.
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Part of the manuscript was prepared while the author enjoyed the hospitality of the Division of Biology, Kansas State University, Manhattan. In particular, the author wishes to express his gratitude to Dr. L. E. Roth and Dr. Jane Westfall for helpful discussion. He also acknowledges the skillful technical assistance of Mrs. Brigitte Gauss. This investigation was supported by the Deutsche Forschungsgemeinschaft.
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Bardele, C.F. A microtubule model for ingestion and transport in the suctorian tentacle. Z.Zellforsch 126, 116–134 (1972). https://doi.org/10.1007/BF00306784
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DOI: https://doi.org/10.1007/BF00306784