Spectral and functional characterization of the green alga Dunaliella salina under increase of NaCl content

Abstract

Spectral and functional characteristics of the photosynthetic apparatus in D. salina cells under increase of NaCl content were investigated. Cells were grown in the medium containing 2 M NaCl at 25°C under continuous light at 200 µmol photons m-2s-1 and in the linear logarithmic phase of grows were transferred to the high salt concentration (4 M NaCl). We have determined that cell division continues, albeit at a slower rate and the rate of chlorophyll biosynthesis is lowered upon transfer to high salt conditions. To compare capacities of photosynthetic activity in the cells grown under various salt concentrations the photosynthetic O2 evolution and respiration intensity were measured. The results show that with the increase of NaCl concentration from 2 to 4 M, photosynthesis intensity falls and intensity of respiration is unchangeable. It is supposed that D. salina cell response to salinity of the medium by reconstruction of their photosynthetic metabolism. The remarkable differences were observed between 77 K fluorescence spectra of D. salina cells from low and high salt media. In D. salina cells cultivated at low salt concentration the maximum emission peak was observed at 686 nm, whereas in high salt media the maximum emission peak shifted to 715 nm. The peak at 686 nm results from emission of chlorophyll a associated with photosystem (PS) II, whereas the emission peak at 710 nm associated with PSI. When the D. salina cells grown at low salt media were transferred to high salt media, the intensity of emission peak at 686 nm decreased with the increase of emission peak at 710 nm. These data suggest the activation of PS I mediated electron flow under high salt conditions.