Short-term effects of solar ultraviolet radiation on the photochemical efficiency of Spirulina platensis in non-aerated and aerated cultures

Continuous depletion of the stratospheric ozone layer results in increasing solar ultraviolet radiation(UVR) reaching the earth's surface. Which has been considered to affect living organisms. Solar UVR may also affect a variety of physiological and biochemical processes in the economic cyanobacterium, Spirulina platensis. However, little has been documented on the aspect. The present study evaluated the short-term effects of UVR on photochemical efficiency of S. platensis in aerated and non-aerated cultures while exposing it to full-spectrum solar radiation(PAB), solar radiation depleted of UVB(PA) and solar radiation deprived of total UV(P:PAR).It was found that both UVR and PAR inhibited the photochemical efficiency during noontime(11:00-13:00), however, UVR+PAR(PAB) resulted in higher inhibition. In aerated cultures, PAR resulted in 11%similar to 20% compared to the initial value in the morning (07:00), UVR(PAB-P) brought about 9%similar to 31% extra photoinhibition. While in non-aerated cultures, the photochemical effciency could not be detected when exposed to UVR. The greatest inhibition was observed at noontime, and the recovery was achieved in late afternoon (17:00) in both the aerated and non-aerated cultures. UVR increased the ratio of carotenoids or phycocyanin to chlorophylla. Compared with PAB and P treatments, cells exposed to PA showed higher values of the pigment ratios, indicating a possibility that UVA may enhance the synthesis of carotenoids and phyocyanin. Although S. platensis was negatively affected by UVR, it tended to develop mechanisms counteracting the damaging effects of UVR during this short-term exposure period, such as down-regulation of the photosynthetic activity of accumulation of the carotenoids