Is Phytomelatonin a New Plant Hormone?

Abstract

Melatonin (N-acetyl-5-methoxytryptamine) is of particular importance as a chronobiological hormone in mammals, acting as a signal of darkness that provides information to the brain and peripheral organs. It is an endogenous synchronizer for both endocrine (i.e., via neurotransmitter release) and other physiological rhythms. In this work we will try to add to the series of scientific events and discoveries made in plants that, surprisingly, confirm the great similarity of action of melatonin in animals and plants. The most relevant milestones on the 25 years of phytomelatonin studies are presented, from its discovery in 1995 to the discovery of its receptor in plants in 2018, suggesting it should be regarded as a new plant hormone.

Daily rhythms of phytomelatonin signaling modulate diurnal stomatal closure via regulating reactive oxygen species dynamics in Arabidopsis

“…[20][21][22] Recently, we identified the first phytomelatonin receptor (PMTR1, previously named CAND2) that regulates stomatal closure via NADPH oxidase-dependent ROS signaling pathway in Arabidopsis, 10 suggesting a possibility that this molecule is a new plant hormone. 10,19,23 Although it has been shown that the endogenous concentrations of phytomelatonin peak during darkness in Chenopodium rubrum as in vertebrates, 24,25 these observations were challenged lately as several publications found that the biosynthesis of melatonin is induced by light but decreased under darkness conditions in morning glory, 26 Arabidopsis 27 and rice. 28 Therefore, it remains controversial whether this newly characterized putative phytohormone is involved in regulation of daily rhythms as the endogenous concentrations of phytomelatonin are always affected by plant growth conditions and environmental factors (eg, temperature, UV light, and water status ).…”

Response of Photosynthetic Performance to Drought Duration and Re-Watering in Maize

“…Drought might lead to excessive generation of reactive oxygen species (ROS), which can cause oxidative damage to photosynthetic components [19]. The antioxidant enzymes were crucial for controlling excessive levels of ROS, and some plant growth regulators, such as melatonin, were used to improve the antioxidant enzyme activity and scavenge ROS under drought [20,21].Maize is an important food and feed crop around the world and is also widely used in industrial products. The effects of drought on maize have been extensively investigated.…”

Variation in surface properties, metabolic capping, and antibacterial activity of biosynthesized silver nanoparticles: comparison of bio-fabrication potential in phytohormone-regulated cell cultures and naturally grown plants

“…Arnao et al, (2020) have reviewed extensively the importance of phytomelatonin. 38 To this end, the application of exogenous MLN could potentially trigger these responses. Exogenous MLN upregulates the antioxidant system of plants to protect them against reactive oxygen species.…”