| Microalgae plays an important role as a primary producer in Arctic hydrology system.Two representative algae species were collected in summer of 2006 from Yellow River Station locating in the Arctic and employed in present research.The results are as follow.1.Effects of UV-B on the growth of Chlorella sp.was investigated under 0(CK), 22μw/cm2,45μw/cm2 and 70μw/cm2 UV-B intensities.UV-B inhibited growth of Chlorella sp.significantly,the higher intensity of UV-B applied the stonger inhibition of algae growth.2.The ultrastructure of Chlorella sp.was investigated by TEM.Chloroplast,Golgi, mitochondria of Chlorella sp.were damaged seriously under 95μw/cm2 UV-B irradiation.3.Growth of Chlorella sp.was monitored under 0(CK),22μw/cm2,45μw/cm2 and 70μw/cm2 UV-B.The results showed that,compared with the control,with increase in UV-B intensity content of chlorophyll a(Chla) corresponsively decreased by 12%,22% and 31%,and content of carotenoid(Car) declined by 8.67%,44.57%and 71.67%, respectively.In contrast,MDA increased by 4.10,9.93 and 29.43 nmol/g(FW).Under UV-B intensity of 45μw/cm2 and 70μw/cm2,superoxide(SOD) dismutase activity increased by 21.3%and 74.6%,respectively.4.Biology effects of UV-B radiation on microalgae were further investigated.Treated with 76μw/cm2 UV-B for 12d,SOD,Catalase(CAT) and active oxygen ingredient of Chlorella sp.cells increased with a peak on 4d while the control maintaind nearly constant.Meanwhile,content of Chlorella sp.fat acid raised by 124%and the soluble protein droped to 80%of the control.Treated Chlorella sp.with 45μw/cm2 UV-B for 12h, contents of Chla and Car reached the maximum level at 4h with 12.8×10-12 and 4.5×10-12mg/cell,respectively.Their contents droped hereafter.Under UV-B intensity of 76μw/cm2,contents of Chla and Car showed a significantly downward trend,whereas malondialdehyde(MDA) and superoxide anion radical(O2-) elevated obviously with prolonging the UV-B radiation and H2O2 was promoted to reach a peak at 12h,but no soignificant changes detected in control.However,the response of Fragilaria sp.to the UV-B treatments was not such obvious.Our results also demonstrated that UV-B (76μw/cm2) treated for 12h changed the fatty acid composition of Chlorella sp..The ratio of total polyunsaturated fatty acids decreased while the ratio of saturated fatty acids increased.The fatty acids of C16:0 and C18:3 increased as well.In conclusion,the response of Arctic microalgae in morphology,ultrastructure and biochemical compositions is a reflection of the acclimation to strong UV-B environment of the Arctic.
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