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ESTABLISHMENT OF MINIMAL AND MAXIMAL TRANSCRIPT LEVELS FOR NITRATE TRANSPORTER GENES FOR DETECTING NITROGEN DEFICIENCY IN THE MARINE PHYTOPLANKTON ISOCHRYSIS GALBANA (PRYMNESIOPHYCEAE) AND THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE)1
Article first published online: 28 JUL 2009
© 2009 Phycological Society of America
Journal of Phycology
Volume 45, Issue 4, pages 864–872, August 2009
How to Cite
Kang, L.-K., Hwang, S.-P. L., Lin, H.-J., Chen, P.-C. and Chang, J. (2009), ESTABLISHMENT OF MINIMAL AND MAXIMAL TRANSCRIPT LEVELS FOR NITRATE TRANSPORTER GENES FOR DETECTING NITROGEN DEFICIENCY IN THE MARINE PHYTOPLANKTON ISOCHRYSIS GALBANA (PRYMNESIOPHYCEAE) AND THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE). Journal of Phycology, 45: 864–872. doi: 10.1111/j.1529-8817.2009.00698.x
Received 14 November 2007. Accepted 16 March 2009.
- Issue published online: 26 AUG 2009
- Article first published online: 28 JUL 2009
- high-affinity nitrate transporter genes;
- Isochrysis galbana;
- nitrogen deficiency;
- relative expression assay;
- Thalassiosira pseudonana
Nitrate transporter genes (Nrt2) encode high-affinity nitrate transporters in marine phytoplankton, and their transcript levels are potential markers of nitrogen deficiency in eukaryotic phytoplankton. For the proper interpretation of measured Nrt2 transcript abundances, a relative expression assay was proposed and tested in Isochrysis galbana Parke (Prymnesiophyceae) and Thalassiosira pseudonana (Hust.) Hasle et Heimdal (Bacillariophyceae). The minimal transcript levels of Nrt2 genes were achieved by the addition of 100 μM ammonium, which led to a rapid decline in Nrt2 transcripts in 10–30 min. Experiments using a concentration series revealed that the effective dosage of ammonium to create a minimal transcript level of ∼1 μmol · mol−1 18S rRNA was ≥25 μM in both species. On the other hand, the addition of l-methionine sulfoximine (MSX), an inhibitor of glutamine synthetase, enhanced the Nrt2 transcript level in I. galbana but did not affect that in T. pseudonana. Nitrogen deprivation was used as an alternative means to create maximal Nrt2 transcript levels. By transferring cells into N-free medium for 24 h, Nrt2 transcript levels increased to ∼90 μmol · mol−1 18S rRNA in I. galbana, and to ∼800 μmol · mol−1 18S rRNA in T. pseudonana. The degree of nitrogen deficiency thus can be determined by comparing original Nrt2 transcript levels with the minimal and maximal levels.