Melatonin is a light signaling molecule in plants

Light is used by plants for photosynthesis and as a signal of their environment. Melatonin (MEL) is one of the indoleamine class of plant growth regulators (PGRs). MEL is a potent antioxidant and has roles in plant growth including root induction and stress mitigation as well as regulating circadian rhythms in mammals and potentially in plants. I hypothesized that MEL is a signaling plant growth regulator induced by specific light spectra to initiate a metabolic(s) cascade. To investigate this hypothesis, my specific objectives were: (a) to develop and validate a UPLC-MS/MS method for detection and quantification of MEL, 5HT, and other analytes in the biosynthetic pathway; (b) to determine the effects of specific light spectra on concentrations of MEL, 5HT, and other prevalent PGRs in a Scutellaria model system; (c) to determine whether the Arabidopsis cryptochrome P450 CYP707A responds to changing light spectra and/or exogenous melatonin application in A. thaliana; and (d) to determine the role(s) and point(s) of interaction of MEL in the karrikin signaling pathway. My data show that blue light resulted in consistent detection of MEL in all species of Scutellaria investigated. In S. racemosa blue light exposure resulted in earlier detection of MEL and higher levels than red light treatment, while white and green light exposure increased levels of stress phytohormones. In A. thaliana CYP707A mutants, MEL decreased germination, root length and secondary root production, red light exposure increased root length and blue light decreased secondary root production. A. thaliana karrikin mutants revealed that MEL decreased germination rate Ler ecotypes and was synergistic with KAR2 to promote secondary root production in both Ler and Col ecotypes. These data indicate that the relative amounts of MEL and 5HT are responsive to light spectra and redirect metabolic resources to enable plant adaptations to changing environments. These physiological responses include germination and root development via interactions including the CYP707A and the karrikin signaling pathway. Together, these data improve our understanding of the role of MEL in plant responses to light and photomorphogenesis.Science, Irving K. Barber Faculty of (Okanagan)Chemistry, Department of (Okanagan)Graduat