Effects Of Salt Stress On The Photosynthesis Of The Economic Cyanobacteria Arthrospira (Spirulina) Platensis And Its Mechanism Study

Arthrospira (Spirulina) platensis, as an important economic cyanobacteria, optimizing its growing conditions and improving its production efficency are general concern. Salt stress is a very important environmental factor affecting its growth during the outdoor mass cultivation of A. platensis. This study we investigated the effects of salt stress on the photosynthesis of A. platensis. The main results are as follows:A. platensis cultured at different NaCl concentrations (0,0.4,0.8M) were exposed to full spectrum solar radiation PAB (PAR+UVA+UVB, 280–700nm), solar radiation depleted of UV-B, PA(PAR+UVA , 320-700 nm) or solar radiation filtered out of total UVR, P (PAR, 400–700 nm) in order to investigate the combined effects of solar UVR and salt stress on the photosynthesis and morphology of A. platensis. It showed that the photochemical efficiency of A. platensis was significantly decreased under these two environmental factors. The greatest inhibition was observed at noontime when the solar irradiance level was higher, and this inhibitory effect was accelerated with the increase of salt concentration. Both high level of PAR and UV radiation reduced the D1 protein content. However, no significant changes were observed in the D1 protein content for the cells cultured at low salt concentration on cloudy day, though the photochemical efficiency of A. platensis was seriously inhibited. In contrast, under high concentration of NaCl, solar radiation caused signifincant loss of D1 protein regardless of the weather conditions. In addition, the combined effects of solar UV radiation and salt stress led to serious breakage of the spiral structure of A. platensis. Chlorophyll a and carotenoid content showed no significant changes in A. platensis cultured under 0 and 0.4M NaCl regardless of the weather conditions. 0.8M NaCl resulted in significant decrease of Chlorophyll a content on sunny day.Salt stress inhibited PSII activity whereas stimulated electron transport activity of PSI to about 20%, however, the whole chain electron transport activity was inhibited. The maximum electron transfer rate(rETR max ), light saturation index for photosynthesis( Ik ) and apparent photosynthetic efficiency(α) decreased significantly under salt stress.