Effects Of Enhanced UV-B Radiation On Growth, Biochemical Characteristics And Ultrastructure Of Marine Microalgae

In this paper, several species of marine microalgae were selected to serve as experimental materialsand the effects of enhanced UV-B radiation on the growth, physiological and biochemical characteristicsand ultrastructure were studied by using experimental ecology method, biochemical method andtransmission electron microscopy. The results could supply experimental basis to answer the effects ofenhanced UV-B radiation on marine ecosystem, while provide theoretical evidences to biologicalmonitoring technology of UV-B radiation. The results were shown as following:1. UV-B radiation showed an inhibitory effect on the growth of marine microalgae. The sensitivityorder of five species of marine microalgae to UV-B radiation was Isochrysis galbana> Phaeodactylumtricornutum> Chaetoceros minutissimus> Chlorella vulgar> Dunaliella salina. Short-term and UV-Bradiation had an apparent inhibition the growth of I. galbana, and low dose of UV-B radiation showedhormesis effect on the growth of P. tricornutum. The growth of marine microalgae were inhibited underhigh dose （U₂and U₃） of long-term UV-B radiation, and low dose （U₁） of long-term UV-B radiationshowed hormesis effect on the growth of marine microalgae.2. The protein synthesis of I. galbana and C. minutissimus were inhibited under short-term UV-Bradiation, soluble protein content of I. galbana was presented more obvious inhibitory effect under thesame dose of UV-B radiation and decreased with dose of UV-B radiation increasing. There was differentactivity change of antioxidant enzyme in three microalgae species to enhanced UV-B radiation, suggestedthey play different role to resist UV-B radiation. Chl-a was presented more obvious inhibitory effect thanCAR under the same dose of UV-B radiation. UV-B radiation showed an inhibitory effect on the growth ofmarine microalgae. The contents of MDA in three microalgae species increased with enhanced UV-Bradiation.3. Chl-a was presented more obvious inhibitory effect than CAR under the same dose of long-termUV-B radiation. Interspecific differences emerged in the activity of antioxidant enzyme to UV-B radiationstress. C. minutissimus showed high activity of antioxidant enzyme, and for I. galbana was relativily low.The contents of MDA in three microalgae species increased with with extending time of UV-B radiation.4. The results indicate that different inoculation densities led to a growth difference of microalgal cells.When the growth of these two algal species was compared,similar effects were observed. With increased,four microalgae species entered the exponential growth phase and retreated to the plateau phase faster, butthe maximum cell density achieved on the growth reduced. Different inoculums and sensitivity differenceto UV-B radiation result in the change of interspecific competition between marine microalgae.5. Transmission electron microscope was selected to examine the effect of enhanced UV-B irradiationon the ultrastructure of C. vulgar. After exposure to2.25J.m^-2 UV-B irradiation, dramatic ultrastructurechange occurred in C. vulgar were observed: thylakoid lost and lamellae disintegration, and thearrangement of thylakoid was confusion. Cell wall were thickened and slight plasmolysis was found insome C. vulgar cells. After exposure to4.5J.m^-2 UV-B irradiation, the arrangement of thylakoid wasconfusion and disintegration, cytoplasm bacame dense, and plasmolysis was found in most C. vulgar cells.The number of mitochondrion and vacuole increased and some cristae of mitochondria were dissolved.