Adaptation involved in nitrogen metabolism in sea ice alga Chlamydomonas sp. ICE-L to Antarctic extreme environments
2015
Wang, Dong S. | Xu, Dong | Wang, Yi T. | Fan, Xiao | Ye, Nai H. | Wang, Wen Q. | Zhang, Xiao W. | Mou, Shan L. | Guan, Zheng
There are several well-described acclimation mechanisms in sea ice-based algae, but little is known about their primary nitrogen metabolism. This study examined nitrogen uptake, nitrate reductase gene (nr) expression, and nitrate reductase activity (NRA) in an Antarctic microalga Chlamydomonas sp. ICE-L relative to altered photoperiod, nitrogen source, and salinity. Both nr expression and NRA varied diurnally over two 24-h light/dark cycles. nr expression reached maximum levels at the end of the light cycle and decreased during the dark period, and the peak in NRA occurred 12 h later than the peak in nr expression. After transfer to continuous light (LL) or continuous dark (DD), this periodicity was abolished, and both parameters were regulated by light availability. Chlamydomonas sp. ICE-L could assimilate both NO₃–N and NH₄–N as nitrogen sources, but the alga preferred NH₄–N when both were present in culture media at the same concentration. The presence of NH₄⁺suppressed nr expression and NRA. Consistent with the regulation of nr expression, the highest NRA was also observed in cells grown in media supplemented with KNO₃. Salinity significantly (P <0.05) affected nr expression and NRA. Both of these parameters were down-regulated with an increase in salinity from 32 to 160 ‰.
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