Some observations on the structure and function of the dinoflagellate pusule

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Abstract
The pusules of an armoured dinoflagellate (Prorocentrum micans) and an unarmoured species (Amphidinium carterae) were examined for effects of certain physicochemical factors, physiological inhibitors, and cytological markers. Fluxes in both salinity and temperature caused pusular size changes, while colchicine, cytochalasin B, and pH changes (in the range 6.0–8.0) had little or no effect. The treatment with solutions of horseradish peroxidase, cationized ferritin, and lectins indicated uptake of these macromolecules via the flagellar canal into the pusules of both dinoflagellates. A three-dimensional model is proposed for the A. carterae pusule based on sequential sections examined by TEM. It is suggested that a fibrillar collar system, in conjunction with the flagellar beating, plays a crucial role in regulating the flow of materials in and out of the pusule. The overall results suggest a multiple function for the dinoflagellate pusule, including osmoregulation, macromolecule uptake, and probably, secretion.