Karyology of a Marine Non-Motile Dinoflagellate, Pyrocystis lunula

Dinoflagellates have a unique and interesting intracellular architecture such as permanently condensed chromosomes throughout the cell cycle. However the study of dinoflagellate chromosomes is not amendable because of the unusually higher number of chromosomes and problems in sample preparation. The species of Pyrocystis spend most of their life cycle as vegetative cyst forms and have been used as experimental organisms for bioluminescence and circadian rhythms. Here, we documented the content of DNA in different life stages and the chromosome karyology in a marine non-motile dinoflagellate Pyrocystis lunula, through light and fluorescent microscopy, serial ultra-thin sectioning, and three dimension (3D) modeling. The DNA content doubles during DNA synthesis and in the end of the cell division two separate daughter cells have the approximately same fluorescent values for the mother cells. Using serial ultra-thin sectioning and 3D modeling, we report the first ultrastructural karyogram. The cells chosen were at the end of karyokinesis. A total of 98 chromosomes were counted and assigned to 49 pairs. In this species, DNA synthesis appears to occur before, or during asexual division and P. lunula lives a diplontic life cycle.