title: Characterization of tryptamine 5-hydroxylase and serotonin synthesis in rice plants.
abstract: 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.
authors.affiliation: Department of Molecular Biotechnology, College of Agriculture and Life Sciences, Agricultural Plant Stress Research Center, Biotechnology Research Institute, Chonnam National University, Gwangju 500-757, South Korea.
authors.forename: S
authors.initials: S
authors.lastname: Kang
authors.forename: K
authors.initials: K
authors.lastname: Kang
authors.forename: K
authors.initials: K
authors.lastname: Lee
authors.forename: K
authors.initials: K
authors.lastname: Back
mesh_terms: D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004298:Dopamine / Q000494:pharmacology; D004789:Enzyme Activation; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D009655:Octopamine / Q000494:pharmacology; D012275:Oryza / Q000187:drug effects / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism*; D012701:Serotonin / Q000096:biosynthesis*; D014363:Tryptamines / Q000494:pharmacology; D014364:Tryptophan / Q000031:analogs & derivatives / Q000494:pharmacology; D014439:Tyramine / Q000494:pharmacology
chemical_list: D014363:Tryptamines; D009655:Octopamine; D012701:Serotonin; C030820:tryptamine; D014364:Tryptophan; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; C407366:tryptamine 5-hydroxylase; D004298:Dopamine; D014439:Tyramine