科研之友
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摘要
Heterosigma akashiwo (Hada) Hada ex Y. Hara et Chihara is a bloom-forming alga that has been associated with fish kills in coastal regions worldwide. Dense blooms of this species occur annually in Delaware's inland bays, USA. Under static laboratory conditions, however, H. akashiwo is a poor competitor compared to other algal species. Instead, Heterosigma may proliferate under dynamic conditions due to its ability to respond quickly to nutrient input. The objectives of this investigation were to examine changes in transcriptional expression of nitrate reductase (NR) as a proxy for nitrate assimilation in Heterosigma. Here, the gene sequence for H. akashiwo nitrate reductase (NR1) was amplified by PCR, and the full-length gene sequence was obtained and characterized. Using quantitative reverse transcriptase real-time PCR (QRT-PCR), changes in NR1 expression were evaluated in relation to temperature and nitrogen status. Expression of NR1 was not significantly different for cultures acclimated to temperatures ranging from 18 degrees C to 28 degrees C. Results also demonstrated that NR1 was expressed constitutively, even in the absence of nitrate and in the presence of ammonium. An apparent biphasic expression of NR1 was observed upon addition of nitrate to N-starved cultures, with significant increases at 15 and 60 min after addition. In contrast, addition of nitrate to nitrate-replete cultures resulted in a significant decrease in NR1 transcript abundance, likely due to repression by downstream products of nitrate assimilation. These results suggest that Heterosigma responds rapidly to changes in the environment by up- or down-regulating the NR transcript pool in relation to the nitrogen status of the cell.
- 出版日期2010-2
