ABSTRACT
ABSTRACT Serotonin and melatonin are two indoleamines widely distributed in plants, well known due to their function as neurotransmitters in mammals. Since they share structural similarity with indole-3-acetic acid (IAA), previous reports suggested a possible auxin activity for these compounds. However, detailed analyses of root architecture have shown that in contrast to serotonin, which represses primary root growth, lateral root formation, and root hair development in high concentrations, melatonin had the opposite effect, promoting lateral and adventitious root formation without affecting primary root growth, and minimally affecting root hair development. These data indicate that indoleamines affect root morphogenesis in a differential and contrasting manner. Accumulating information further suggests a critical role of serotonin and melatonin in abiotic stress tolerance, regulation of senescence, activation of defense responses, plant productivity, and developmental phase transitions, which may be related to antioxidant and growth-promoting properties. In this chapter, we discuss possible mechanisms of serotonin and melatonin sensing in model and crop plants.
