DOI: 10.5176/2251-2489_BioTech32
Authors: Yeong Byeon, Sangkyu Park, Young Soon Kim and Kyoungwhan Back
Abstract: Melatonin is a naturally occurring compound found in animals, plants and microbes. In animals, circulating levels of melatonin vary in a daily cycle, allowing the entrainment of the circadian rhythms of biological functions. In this experiment, detached rice leaves were incubated in either continuous light or dark condition to examine the light-responsive regulation of melatonin biosynthesis and its precursors, such as tryptophan, tryptamine, serotonin, and N-acetylserotonin. In the continuous light, there was 55-fold increase in serotonin content in the rice leaves at 10 d compared to the continuous dark, which resulted in the accumulation of melatonin only in the light condition. The increase of serotonin contents in the continuous light was accompanied by the induced tryptophan decarboxylase1 (TDC1) and tryptamine 5-hydroxylase (T5H) transcripts, but the induced transcript levels were also observed in the continuous dark although their levels were slightly lower than those found in the continuous light. No difference in N-acetylserotonin methyltransferase (AMT15) mRNA expression was observed between the continuous light and continuous dark periods. Contrary to the transcript levels, significant difference was observed in T5H protein levels where a huge induction of T5H protein was detected in the continuous light whereas a low level of T5H protein was found in the continuous dark, suggesting that T5H protein level was responsible for the induced melatonin biosynthesis in the senesced leaves of rice under the continuous light condition.
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