Journal
JOURNAL OF PINEAL RESEARCH
Volume 52, Issue 2, Pages 211-216Publisher
WILEY
DOI: 10.1111/j.1600-079X.2011.00930.x
Keywords
5-hydroxytryptophan; melatonin; N-acetylserotonin; N-acetyltryptamine; rice; senescence; serotonin; tryptamine; tryptamine 5-hydroxylase
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Funding
- Rural Development Administration [PJ00811201]
- National Research Foundation of Korea (NRF) [2011-0013092]
- National Research Foundation (NRF) by the Ministry of Education, Science and Technology (MEST), Korea Government [2011-0018393]
- Rural Development Administration (RDA), Republic of Korea [PJ009491052013] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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Melatonin biosynthesis was examined in Sekiguchi mutant rice lacking functional tryptamine 5-hydroxylase (T5H) activity, which is the terminal enzyme for serotonin biosynthesis in rice. During senescence process, the leaves of Sekiguchi mutant rice produced more tryptamine and N-acetyltryptamine compared with the wild-type Asahi leaves. Even though T5H activity is absent, Sekiguchi leaves produce low levels of serotonin derived from 5-hydroxytryptophan, which was found to be synthesized during senescence process. Accordingly, both rice cultivars exhibited similar levels of N-acetylserotonin until 6 days of senescence induction; however, only Asahi leaves continued to accumulate N-acetylserotonin after 6 days. In contrast, a large amount of N-acetyltryptamine was accumulated in Sekiguchi leaves, indicating that tryptamine was efficiently utilized as substrate by the rice arylalkylamine N-acetyltransferase enzyme. An increase in N-acetyltryptamine in Sekiguchi had an inhibitory effect on synthesis of melatonin because little melatonin was produced in Sekiguchi leaves at 6 days of senescence induction, even in the presence of equivalent levels of N-acetylserotonin in both cultivars. The exogenous treatment of 0.1 mmN-acetyltryptamine during senescence process completely blocked melatonin synthesis.
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