Abstract
Ecdysis, the process of extensive cell covering rearrangement, represents a remarkable physiological trait of dinoflagellates. It is involved in the regulation of the population and bloom dynamics of these microorganisms, since it is required for the formation of their thin-walled cysts. This study presents laboratory data on ecdysis in Prorocentrum cordatum, a harmful dinoflagellate species of high environmental significance. We studied external stressors triggering this process and changes in the cell ultrastructure accompanying it. Our experiments showed that mass ecdysis and formation of cysts in P. cordatum could be induced by centrifugation, temperature decrease, changes in salinity, and treatment by 2,6-dichlorobenzonitrile, whereas temperature increase, changes in pH and treatment by tetracycline did not have this effect. Obtained cysts of P. cordatum did not contain the pellicular layer and were formed in the end of the first stage of this process, i.e. removal of the plasma membrane and the outer amphiesmal vesicle membrane, whereas its second stage, removal of theca, represented excystment. Based on our findings, we conclude that such cysts can be attributed to thecate cysts and suggest P. cordatum as a promising model organism for the investigation of cellular and molecular aspects of ecdysis in dinoflagellates.
Highlights
Dinoflagellates are eukaryotic microorganisms widely spread in marine and freshwater environments over the globe
Their thecal plates could be stained by Calcofluor due to the plasma membrane and outer amphiesmal vesicle membrane damage
Ecdysed cells that had not yet finalised the arrangement of the new full amphiesma looked spherical compared to the cells retaining old thecae and cells with new mature thecal plates (Fig. 1b), but otherwise they appeared to be very similar to vegetative cells and were motile stressed by heating during the microscopic observation (Supplementary Video 2)
Summary
Dinoflagellates are eukaryotic microorganisms widely spread in marine and freshwater environments over the globe. Dinoflagellates are remarkable due to many traits of their morphology and physiology One of their fascinating features is a complex cell covering consisting of the plasma membrane underlain by amphiesmal vesicles which may contain significant amount of cellulose forming thecal plates (armoured species) or no/minor amount of cellulose (naked species). An additional non-membrane pellicular layer is present inside amphiesmal v esicles[4,5,6,7,8] Both armoured and naked species are capable of cell covering rearrangement in response to stressful environmental c onditions[7]. Shedding of membranes and thecal plates (if present) is called ecdysis (see[8], and references therein) This process was shown to occur in many dinoflagellate species, e.g. in Heterocapsa niei[9], Kryptoperidinium foliaceum The external factors triggering the formation of thinwalled cysts in different dinoflagellates include changes in temperature[23,24,25,26] and light regime[27], nutrient depletion and culture ageing[28,29], as well as treatment by indoleamines[30]
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