Survival Strategy of the Diatom Pseudo-nitzschia pungens (Grunow ex Cleve) Hasle, 1993 under Long-term Dark Conditions

The physiological response of the marine diatom Pseudo-nitzschia pungens to dark exposure for 45 and 90 days and subsequent acclimation under re-illumination was studied. We have shown that the alga remains metabolically active between 0 and 45 days of dark exposure. This stage is characterized by the stabilization of cell culture density, activation of respiratory metabolism and synthetic processes, and a low rate of intracellular carbon (C) and nitrogen (N) consumption. Between 45 and 90 days of dark exposure, P. pungens cells enter a rest state accompanied by the cessation of cell division, suppression of synthetic processes, preservation of the light-harvesting complex, and almost complete suppression of photosynthesis. The viability of cells is provided by maintaining high respiratory activity and elevated level of intracellular C reserves. We have also shown that the step-by-step reorganization of the structure and function of the photosynthetic apparatus in P. pungens under long-term dark conditions contributes to the maintenance of cell’s photosynthetic competence and the subsequent recovery of the density of P. pungens population when re-exposed to light. The duration of the algae population recovery period, as well as the regeneration of the structure of their light-harvesting complex, is determined by the duration of exposure to darkness.