The Regulation Effects and Associated Physiological Mechanisms of Exogenous Melatonin on Sorghum Under Drought Stress

Sorghum (Sorghum bicolor L.) is a vital crop for both grain production and forage, playing a critical role in ensuring global food security and sustainable livestock production. Drought stress represents one of the most severe abiotic constraints in sorghum cultivation, adversely affecting plant growth and development, and ultimately leading to significant reductions in yield and quality. Melatonin has emerged as a multifaceted plant growth regulator that enhances plant growth and confers tolerance to various abiotic stresses. It actively participates in regulating key physiological processes, including seed germination, seedling establishment, cellular development, and metabolic homeostasis. This review synthesizes current knowledge on the impacts of drought stress on sorghum growth and physiological metabolism, with a specific focus on the protective role of melatonin under water-deficit conditions. The underlying physiological and molecular mechanisms are comprehensively discussed, encompassing ion homeostasis, nutrient metabolism, reactive oxygen species (ROS) scavenging, photosynthetic efficiency, energy metabolism, phytohormone crosstalk, signal transduction, and associated gene expression. Finally, we outline future research directions to advance our understanding of melatonin-mediated drought tolerance in sorghum, providing insights for breeding drought-resilient varieties and developing high-yielding cultivation strategies.