Features of the Structural and Functional Characteristics of the Diatom Alga Pseudosolenia calcar-avis.

The structural and functional characteristics of the large-celled diatom alga Pseudosolenia calcar-avis isolated from the Black Sea plankton have been studied. The main reasons for its intensive development and dominance in the Black Sea phytoplankton under conditions of different nutrient content in water have been determined. The high values of the photosystem II efficiency (0.67–0.69), relative chlorophyll a content (~1% of the organic carbon), and the ratio of the cell surface area to cytoplasm volume (~0.80–0.90 μm^–1), as well as the presence of a large intracellular vacuole, allowed this species to grow at a high rate (1.40 day^–1) under optimal environmental conditions. The transfer of P. calcar-avis cells having the maximum intracellular pool of nutrients to seawater depleted in nutrients causes a rapid decrease in photosystem II efficiency, relative content of chlorophyll a, and specific growth rate. Due to the intracellular pool of nutrients, this algal species provides 4.5 cell divisions within 4 days. After the depletion of intracellular nutrient reserves, the cell abundance and the culture viability remains almost unchanged for the next 5–7 days. The complete restoration of the functional activity and the further growth of this species require access to the external source of nutrients able to maintain cell functioning at a high level. The possible mechanisms of the replenishment of P. calcar-avis cells with nutrients under conditions of their deficiency in the seawater are discussed. [ABSTRACT FROM AUTHOR]