Effects of Prolonged UV-B Enhanced Fluorescent Radiation on Some Marine Microalgae

The eukaryotic unicellular microalgae Chlorella salina, Dicrateria inornata, and Isochrysis galbana were grown under control (fluorescent 20 W m^–2) and UV-B enhanced (UV-B^E, 0.5 W m^–2) fluorescent radiation. The growth rate showed marginal increase under UV-B^E. Decrease in protein content was observed in Dicrateria cells but in Chlorella an initial increase up to 4 d and in Isochrysis an increase at days 4 and 5 was noted. The chlorophyll a content showed marked increase in Chlorella and Isochrysis but in Dicrateria a decline was found. UV-B^E reduced the photosynthetic activity in all three species, but the reduction was larger in Chlorella and Dicrateria. Fluorescence excitation spectra for F₆₈₂ in Chlorella cells grown for 5 d under UV-B^E showed reduction in all peaks. In contrast to this, in Dicrateria and Isochrysis cells, the 530 and 590 nm excitation peaks increased with an appreciable decrease in the 466 nm peak. SDS-PAGE analysis revealed significant decrease in the contents of 47, 33, and 23 kDa polypeptides in Chlorella cells. In Dicrateria cells, significant loss in the content of 55, 38, and 18 kDa polypeptides was observed. The content of low molecular mass polypeptides (15 kDa) remained unaffected. Isochrysis cells were more stable in preserving the content of thylakoid polypeptides.