Plant Cell Reports

, Volume 26, Issue 11, pp 2009–2015 | Cite as

Characterization of tryptamine 5-hydroxylase and serotonin synthesis in rice plants

  • S. Kang
  • K. Kang
  • K. Lee
  • K. BackEmail author
Physiology and Biochemistry


Serotonin is a well-known pineal hormone that in mammals plays a key role in mood. In plants, serotonin is implicated in several physiological roles such as flowering, morphogenesis, and adaptation to environmental changes. However, its biosynthetic enzyme in plants has not been characterized. Therefore, we measured the serotonin content and enzyme activity responsible for serotonin biosynthesis in rice seedlings. Tryptamine 5-hydroxylase (T5H), which converts tryptamine into serotonin, was found as a soluble enzyme that had maximal activity in the roots. The maximal activity of T5H was closely associated with the enriched synthesis of serotonin in roots. Tetrahydropterine-dependent T5H activity was inhibited by tyramine, tryptophan, 5-OH-tryptophan, and octopamine, but remained unaltered by dopamine in vitro. The tissues of rice seedlings grown in the presence of tryptamine exhibited a dose-dependent increase in serotonin in parallel with enhanced T5H enzyme activity. However, no significant increase in serotonin was observed in rice tissues grown in the presence of tryptophan, suggesting that tryptamine is a bottleneck intermediate substrate for serotonin synthesis.


5-OH-tryptophan Octopamine Serotonin Tryptamine Tryptamine 5-hydroxylase 



Aromatic l-amino acid decarboxylase


Fresh weight


Tryptamine 5-hydroxylase


Tryptophan decarboxylase


Tryptophan hydroxylase





This study was supported by the SRC program from the Korea Science and Engineering Foundation (KOSEF) through the Agricultural Plant Stress Research Center Program grant no. R11-2001-09203001-0.


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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  1. 1.Department of Molecular Biotechnology, College of Agriculture and Life Sciences, Agricultural Plant Stress Research CenterBiotechnology Research Institute, Chonnam National UniversityGwangjuSouth Korea

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