Abstract: The PtAspATs enzyme activities and their transcripts levels were determined by native gel assay and quantitative real time RT-PCR (qPCR) respectively, in different tissues of Populus trichocarpa exposed to 0 mmol/L, 2 mmol/L and 10 mmol/L nitrogen concentrations. It was found that nitrogen deficiency resulted in the decrease of PtAspAT enzyme (including mitochondria, cytosol and plastid PtAspAT isozymes) activities in young leaves, stem segments and roots, but no significant change in mature leaves; meanwhile, at the transcript level, most of the PtAspAT genes showed a downward expression trend except for PtAspAT1, 2, 6 and 7. Under high nitrogen treatment, the PtAspAT enzyme (including mitochondria, cytosol and plastid PtAspAT isozymes) activities in the stem and root were significantly increased, but which in the leaves were decreased slightly, whereas at the transcript level, most PtAspAT gene transcripts were increased except for PtAspAT4, 5 and 6. Noteworthy, the mitochondria PtAspAT isozyme activities were increased with the increase of nitrogen concentration. However, this change was not coupled with corresponding PtAspATs mRNA, indicating that PtAspATs are subject to a complex regulatory control (e.g. post-transcriptional or post-translational control) in P. trichocarpa. This study would lay an important foundation for further study of the physiological role and regulation mode of aspartate aminotransferase in plants.

Key words: Populus trichocarpa, aspartate aminotransferase, nitrogen treatment, gene expression