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

In cells of a culture of the large diatom Ditylum brightwellii (T. West) Grunow acclimated to weak light (17 μmol photons/(m2 × s)), numerous chloroplasts were 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 formed in the center of the cell, which continued until the end of the two-hour exposure period. At light intensities of 510–935 µmol/(photons/(m2 × s) during short-term photoacclimation, chloroplast aggregation was noted for 20–60 min, after which their reverse movement and uniform distribution in the cytoplasm were 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 retained their viability for only six hours. Long-term photoacclimation of this species, which ended by the end of the second day, was detected when the light weakened by about 2 times. It was expressed as an increase in cell volume and C/Chl a ratio, increased aggregation of chloroplasts in the center of the cell, and a decrease in a number of fluorescent parameters reflecting the efficiency of photosystem II and culture viability.