Abstract
Melatonin, a multifunctional signaling molecule, is ubiquitously distributed in different parts of a plant and responsible for stimulating several physiochemical responses against adverse environmental conditions in various plant systems. Melatonin acts as an indoleamine neurotransmitter and is primarily considered as an antioxidant agent that can control reactive oxygen and nitrogen species in plants. Melatonin, being a signaling agent, induces several specific physiological responses in plants that might serve to enhance photosynthesis, growth, carbon fixation, rooting, seed germination and defense against several biotic and abiotic stressors. It also works as an important modulator of gene expression related to plant hormones such as in the metabolism of indole-3-acetic acid, cytokinin, ethylene, gibberellin and auxin carrier proteins. Additionally, the regulation of stress-specific genes and the activation of pathogenesis-related protein and antioxidant enzyme genes under stress conditions make it a more versatile molecule. Because of the diversity of action of melatonin, its role in plant growth, development, behavior and regulation of gene expression it is a plant’s master regulator. This review outlines the main functions of melatonin in the physiology, growth, development and regulation of higher plants. Its role as anti-stressor agent against various abiotic stressors, such as drought, salinity, temperatures, UV radiation and toxic chemicals, is also analyzed critically. Additionally, we have also identified many new aspects where melatonin may have possible roles in plants, for example, its function in improving the storage life and quality of fruits and vegetables, which can be useful in enhancing the environmentally friendly crop production and ensuring food safety.
Highlights
Melatonin (N‐acetyl‐5‐methoxytryptamine), an indoleamine, was first isolated in 1958 from the bovine pineal gland [1] and named according to its role in reversing the darkening effect of the melanocyte‐stimulating hormone [2]
Melatonin is considered as a master plant regulator as it stimulates plant growth and development by acting as signaling molecule associated with defense mechanisms against different biotic and abiotic stresses like cold, drought, salinity and nutritional deficiencies [14,15]
The melatonin role against UV‐B was studied by another scientist, who proposed that damage to DNA was highly diminished in Nicotiana sylvestris plant species when exposed to UV‐B radiation as this transgenic specie expresses a synthesis gene of melatonin [49]
Summary
Melatonin (N‐acetyl‐5‐methoxytryptamine), an indoleamine, was first isolated in 1958 from the bovine pineal gland [1] and named according to its role in reversing the darkening effect of the melanocyte‐stimulating hormone [2]. Melatonin is considered as a master plant regulator as it stimulates plant growth and development by acting as signaling molecule associated with defense mechanisms against different biotic and abiotic stresses like cold, drought, salinity and nutritional deficiencies [14,15]. It is involved in multiple physiological actions such as photosynthesis, seed germination that occurs in plants [16]. We speculate on new potential aspects where melatonin may have possible functions in plants
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