Diel changes in pyrenoid and starch reserves in dinoflagellates

Abstract

The ultrastructure and lectin-labelling characteristics of dinoflagellate starch and pyrenoids were compared between day-and night-phase cells of two marine and three freshwater dinoflagellates (Clenodinium sp., Lingulodinium polyedrum, Peridinium inconspicuum, P. volzii and Pyrocystis lunula), using electron microscopy and fluorescent lectins. During the day, all cells possessed large starch granules adjacent to their plastids, with the pyrenoid regions located towards the cell centre. In all species, pyrenoids, plastids and starch granules showed a radial distribution emanating from the cell centre. During the night, pyrenoid regions were absent from both marine and freshwater species; starch granules were absent from the marine forms but remained present in the freshwater forms. The results demonstrate that pyrenoids show a diurnal rhythm in occurrence in both freshwater and marine dinoflagellates and that starch reserves are consumed differently in marine and freshwater forms.