The development of cell coverings in armored dinoflagellates by electron microscopy

Abstract

Motile dinoflagellates are bound by a complex cell covering, termed amphiesma. The cell covering consists of the plasma membrane, amphiesmal vesicles, and microtubules arrays lying under the amphiesmal vesicles. Armored dinoflagellates have amphiesmal vesicles containing thecal plates. Thecal plate pattern defined by the number, shape and arrangement of thecal plates is one of the most important characters to classify these armored dinoflagellate species. The present study demonstrated how amphiesmal vesicles develop after ecdysis in the armored dinoflagellate Scrippsiella hexapraecingula. In this report, we show the three-dimensional aspects of cortical membrane systems including the developing amphiesmal vesicles, which were visualized by both freeze-fracture and thin sectioning methods. Furthermore, the possible role of cortical microtubules in dinoflagellates was studied using high-pressure treatments. During the nonmotile phase, one or two daughter cells are produced inside the pellicle, and they develop new amphiesmal vesicles. The amphiesmal vesicles are empty, but are arranged in the same pattern as the developing thecal plates. Thecal plates are produced in the amphiesmal vesicles of motile cells, and therefore thecal plate pattern is determined at the time of development of amphiesmal vesicles in nonmotile cells. After nonmotile cells were exposed to high-pressure treatments sufficient to disorganize the cortical microtubules, they produced new motile cells with thecal plate patterns that differed considerably from the pattern known for this species.