Melatonin: A multi-functional regulator of fruit crop development and abiotic stress response

Melatonin (MEL), which is also known as N-acetyl-5-methoxytryptamine, is an indoleamine that is widely distributed and synthesized from tryptophan. It serves as a fundamental regulator of various physiological processes in plants themselves. These processes include the modulation od cardiac rhythms, immunity, and antioxidation. Additionally, it is a versatile molecule in plants that has been extensively researched for its involvement in stress tolerance, biosynthesis, degradation, and physiological functions. This article summarizes the latest scientific discoveries regarding the effects of melatonin on flowering, fruit maturation, root development, seed germination, and senescence in plants. The article also highlights melatonin multiple pathways of action in alleviating the adverse effects of biotic stresses, including the regulation of the redox state, gene expression and hormone networks. Furthermore, melatonin has been found to alter the contents of secondary metabolites, such as alkaloids, terpenoids, and polyphenols, and to modulate post-harvest fruit ripening by controlling the expression of genes associated with ethylene. Recent finding suggests that melatonin is a crucial player in the plant's reaction to abiotic stress, working in conjunction with various phytohormones, nitric oxide (NO)and reactive oxygen species (ROS). There has been extensive research on the capacity of melatonin to alleviate the impact of different abiotic stresses, such as drought, extreme temperature, salt, and heavy metal stress. Considering its multifaceted functions in in controlling and regulating plant growth and development, we suggest that melatonin is a master regulator in fruit plants.