• Contrasts mepiquat chloride and melatonin across multiple abiotic stress conditions. • Integrates GA–DELLA and melatonin–ROS signaling frameworks for stress tolerance. • Links molecular responses to biomass, yield stability and grain quality under stress. • Identifies key candidate genes and pathways modulated by MC and melatonin. Abiotic stresses such as drought, salinity, extreme temperature, heavy metal toxicity, and ultraviolet (UV) radiation threaten global crop productivity. Two promising exogenous growth regulators, mepiquat chloride (MC), a growth modulating compound, and melatonin (MT), a versatile indolamine were investigated. This review demonstrated that MC enhances stress resilience by inhibiting gibberellin biosynthesis and stabilizing DELLA proteins, promoting root growth, antioxidant activation, and ion homeostasis. In addition, MT acts as both an antioxidant and signaling molecule, scavenging reactive oxygen species (ROS), protecting photosynthesis, and regulating osmotic balance and hormonal crosstalk. These regulators differentially modulate stress-responsive genes, MT upregulates CBF1, RD29A, P5CS, and OsHAK5 , while MC improved antioxidant and ion transport pathways via GA-DELLA interactions. This review synthesizes recent advances in MC and MT applications across crops, examining their physiological effects, molecular regulation, and agronomic impacts on yield and quality. Critical gaps remain in understanding early stress signaling, transcriptional regulators, and their combined effects under field conditions. Integrated molecular-physiological agronomic studies are urgently needed to optimize their synergistic potential for critical development of climate-change-resilient agriculture.
Liu et al. (Sun,) studied this question.