A simple and rapid scanning electron microscope preparative technique for delicate "gymnodinioid" dinoflagellates

Light microscopy (LM) is routinely used to investigate delicate (unarmoured and lightly armoured) "gymnodinioid" dinoflagellate species but at this level of resolution, morphological features such as apical grooves, apical pores, thin thecal plates, and scales are often difficult to observe, thereby necessitating the use of scanning electron microscopy (SEM). Good results were obtained when harvested cells were fixed with osmium tetroxide (OsO4) as the primary fixative, adhered with poly-L-lysine to round glass coverslips, dehydrated in an ethanol series, and dried with hexamethyldisilazane (HMDS). Poly-L-lysine has in the past effectively been used to adhere biological material such as human red blood cells, mouse leukemic cells, and marine dinoflagellates to glass coverslips. HMDS has been used to substitute critical point drying (CPD) to dry soft insect tissues, rat hepatic endothelial cells, and the cilia of rat trachea. By combining and fine-tuning these two protocols in SEM studies of delicate "gymnodinioid" dinoflagellates, it is possible to overcome cell distortion such as shrinking and collapsing that result from centrifuging, filtering, and CPD. The combination of poly-L-lysine and HMDS not only produces good results but also requires limited expertise and equipment, is inexpensive, and is less time-consuming.