Occurrence and Biosynthesis of Melatonin and Its Exogenous Effect on Plants

Melatonin is an endogenous indolamine found in many plants. It has been shown to generate a wide range of metabolic, physiological, and cellular responses, thus affecting growth and development, particularly under different environmental stresses. In the present review, we focus on its role in germination, growth and development, photosynthesis, senescence, and antioxidant activity in plants. Further, an effort has been made to discuss its occurrence, biosynthesis, and relationship with other phytohormones in plants. Moreover, melatonin-mediated signaling and its mechanisms of action under stress conditions in plants have been comprehensively discussed. Finally, its role under various abiotic stress conditions has also been discussed in this review.