Acclimation Strategies for the Black Sea Diatom Algae Ditylum brightwellii to High Intensity of Light

Abstract

In cells of a culture of the large diatom Ditylum brightwellii (T. West) Grunow acclimated to faint light (17 μmol photons/(m² s)), numerous chloroplasts are evenly distributed throughout the cell cytoplasm. After 10 min of exposure of algae to extremely high illumination (1100 μmol photons/(m² s)), their aggregates gradually form in the center of the cell, and their formation continues until the end of the 2-h exposure period. At light intensities of 510–935 µmol photons/(m² s) during short-term photoacclimation, the aggregation of chloroplasts is recorded for 20–60 min, after which their reverse movement and uniform distribution in the cytoplasm are revealed by the end of the second hour. Under conditions of a longer culture stay at a light intensity of 1100 μmol photons/(m² s), the algae retains viability for only 6 h. Long-term photoacclimation of this species, which stops by the end of the second day, is detected when the light becomes half as weak. This is manifested in an increase in cell volume and in the C/Chl a ratio, in the increased aggregation of chloroplasts in the center of the cell, and in a decrease in a number of fluorescent parameters of the efficiency of photosystem II and of culture viability.