Effects Of Solar UV Radiation On The Photosynthesis Of The Economic Cyanobacteria Arthrospira (Spirulina) Platensis And Its Machanism Study

Arthrospira (Spirulina ) platensis is an important economic cyanobacterium and its biologicalcharacteristics have been well documented. Recently, the increasing solar ultraviolet radiation(UVR) has been received great concern. Enhanced UVR might bring about negative effects on A.plantensis, particularly on its photophysiology, howerver, little is known about this. This studyinvestigated the effects of solar UVR on the photosynthesis of A. platensis as well as itsmechanisms . In addition, the interactive effects of solar UVR and salt on A. platensis were alsoexplored. The main results are as follows:The photochemical activity of PSⅡin A. platensis varied with the changes of daily solarradiation. It decreased graually under high photosynthetically active radiation (PAR) and UVRwith the increase of the solar irradiance level, and reached the minimum value at noon, however,it recovered faster in the presence of UVR when the irradiance level was low in the afternoon.Further investigation showed that high PAR and UVR could also inhibit the electron transportrate and reduce the oxygen evolution. The PSⅡactivity showed wavelengh dependence in therange of UV spectra according to the measurement of biological weighting functions (BWFs),shorter wavelength radiation had higher inhibitory effects on PSⅡactivity. We also found thatthe level of initial fluorescence (F0) correlated well with the production of inactive PSⅡcentersdepleted of D1 protein, and the turn over of D1 protein played an important role in the repair ofphotoinhibition induced by UVR and high PAR.Photoinhibition was mainly caused by PAR under high solar radiation level, however,moderate level of PAR could offset partly the inhibitory effects induded by UVR. Our resultsshowed the repair rate (RPSⅡ) in A. platensis under sole UVR was lower, and the functional targetsize for photoinactivation of PSⅡ(σi) was larger as compared with that when the radiationtreatment was supplemented with PAR. A. platensis strain 439, which kept indoors for decades,was more sensitive to UV radiation than the outdoor strain D-0083.The study also showed that solar UV radiation coupled with salt significantly reduced the photochemical effciency of A. platensis D-0083. No significant recovery was shown in A.platensis under the treatments both with UVR and salt during this experimental period (21 days).The interactive effects also broke the trichomes and changed the morphology of A. platensis.