This review summarizes the advances that have been made in terms of the identified functions of
melatonin in plants.
Melatonin is an endogenously-produced molecule in all plant species that have been investigated. Its concentration in plant organs varies in different tissues, e.g., roots versus leaves, and with their developmental stage. As in animals, the pathway of
melatonin synthesis in plants utilizes
tryptophan as an essential precursor molecule.
Melatonin synthesis is inducible in plants when they are exposed to abiotic stresses (extremes of temperature, toxins, increased soil salinity, drought, etc.) as well as to biotic stresses (
fungal infection).
Melatonin aids plants in terms of root growth, leaf morphology,
chlorophyll preservation and fruit development. There is also evidence that exogenously-applied
melatonin improves seed germination, plant growth and crop yield and its application to plant products post-harvest shows that
melatonin advances fruit ripening and may improve food quality. Since
melatonin was only discovered in plants two decades ago, there is still a great deal to learn about the functional significance of
melatonin in plants. It is the hope of the authors that the current review will serve as a stimulus for scientists to join the endeavor of clarifying the function of this phylogenetically-ancient molecule in plants and particularly in reference to the mechanisms by which
melatonin mediates its multiple actions.