Multifaceted Roles of Serotonin in Plants

Abstract

Serotonin (5-hydroxytryptamine) is one of the well studied indoleamine neurotransmitters in vertebrates. This molecule has also been reported from a wide range of plant species in almost all plant families, proving that serotonin is a ubiquitous molecule. Serotonin accumulation has been detected in different parts of the plants like roots, stems, leaves, fruits and seeds; however, the quantity varies in these different tissues. Serotonin in plants is synthesized via two-step process, where tryptophan is first catalyzed into tryptamine by tryptophan decarboxylase, followed by the catalysis of tryptamine by tryptamine 5-hydroxylase to serotonin. Serotonin is an ancient indoleamine that was presumably part of the life cycle of the first prokaryotic life forms on Earth, millions of years ago, where it functioned as a powerful antioxidant to combat the increasingly oxygen-rich atmosphere. Such antioxidative potential of serotonin has been largely exploited in the development of stress tolerance and resistance in plants. Serotonin plays diverse roles in plants including growth and development, energy acquisition, seasonal cycles, modulation of reproductive development, control of root and shoot organogenesis, delay of senescence, and responses to abiotic and biotic stresses. The present article provides an overview of the occurrence and metabolism of serotonin and its multifaceted roles in regulating plant morphogenesis and multiple physiological functions in plants.