Effect of UV-B radiation on photosystem II functions in Antarctic and mesophilic strains of a green alga Chlorella vulgaris and a cyanobacterium Synechocystis salina

Abstract

The green alga Chlorella vulgaris and the cyanobacterium Synechocystis salina cells isolated from Antarctic and mesophilic environments, grown in batch cultures under continuous visible light, were used to assess the effect of the UV-B radiation on the photosystem II (PSII). UV-induced changes in its functional activity were estimated by Pulse Amplitude Modulated chlorophyll fluorescence and oxygen evolution (measured with oxygen rate electrode). The data reveal a relatively stronger UV-B-induced inhibition of oxygen evolution in comparison to that of the primary photochemistry of the PSII in both green algae and cyanobacteria. The inhibition of oxygen evolution was a result of the decrease in the number of functionally active PSII centers. The modification of active reaction centers was also recorded through the relatively more effect on fast operating PSII centers than that of the slow operating PSII centers. On the other hand, the PSII activity of cyanobacteria was more vulnerable to UV-B radiation than that of green algae. Likewise, the mesophilic strain of S. salina was more susceptible to UV-B radiation than the Antarctic isolates.