Development of the pellicle and thecal plates following ecdysis in the dinoflagellateGlenodinium foliaceum

Summary

The ultrastructure and development of the amphiesma of the dinoflagellateGlenodinium foliaceum was studied using conventional electron microscopy and immunocytochemistry. Ecdysis (shedding of the flagella, the outer two membranes of the cell, and the thecal plates) was induced by centrifugation. The cells were resuspended and the thickening of the pellicle and the development of the new thecal vesicles and plates was studied over a 9 h period. After ecdysis, the thin pellicle which underlay the thecal plates in the motile cells thickens to form a complex structure of four distinct layers: an outer layer of randomly oriented fibrils, a 50 nm layer of fibrils oriented perpendicular to the dense layer, the dense layer which has a trilaminate structure, and a wide inner homogeneous layer. The new thecal vesicles form in these pelliculate cells by the migration of electron translucent amphisomal vesicles over the layer of peripheral microtubules to a position directly under the plasmalemma. The thecal vesicles then flatten and elongate. A discontinuous pellicular layer appears within them. Subsequently, the thecal vesicles widen and are filled with a fibrillogranular substance overlying the pelliculate layer. The thecal plates form on top of this fibrillogranular material. By this time, most cells have escaped from the pellicle and are motile. At first, the outer thecal vesicle membrane is continuous with the inner thecal vesicle membrane at the sutures, but when this connection is broken, the dense pelliculate layers become continuous across the suture as does the inner thecal vesicle membrane. At ecdysis, this membrane becomes the new plasmalemma of the cell. Cells at each stage of pellicle thickening and thecal development were labelled with a polydonal antiserum raised against the 70 kDa epiplasmic protein ofEuglena acus. This antiserum labelled both the thecal plates of the motile cells and the inner homogeneous layer of the pellicle of ecdysed non-motile cells. No other amphiesmal structure was labelled, nor was any intracellular compartment.