Introduction:
Climate change is intensifying abiotic and biotic stresses such as drought, salinity, heat waves, and emerging pathogens, threatening global food security. Reactive oxygen species (ROS) have emerged as central regulators of plant adaptation to these stresses. While uncontrolled ROS accumulation induces oxidative damage, controlled ROS signaling modulates growth, defense, and survival under adverse conditions. Deciphering ROS homeostasis is, therefore, crucial for developing climate-smart crop improvement strategies.

Methods:
A comprehensive synthesis of experimental evidence was undertaken, covering ROS generation sites (chloroplasts, mitochondria, peroxisomes, and plasma membrane NADPH oxidases), their quantification under stress, and their interplay with enzymatic (SOD, CAT, APX, and GPX) and non-enzymatic (ascorbate, glutathione, and phenolics) antioxidants. Recent omics-based studies, mutant analyses, and transgenic approaches were reviewed to highlight advances in understanding ROS-mediated stress regulation.

Results:
Evidence indicates that moderate ROS bursts act as critical secondary messengers, activating MAPK cascades, transcription factors (NAC, WRKY, and MYB), and stress-responsive genes. ROS interact synergistically with phytohormones (ABA, ethylene, and salicylic acid) and redox regulators to orchestrate adaptive responses, including stomatal regulation, osmolyte accumulation, and improved water-use efficiency. Climate-resilient genotypes and genetically engineered lines with enhanced antioxidant capacity show superior tolerance to combined stresses, validating ROS management as a breeding target.

Conclusions:
ROS act as pivotal modulators of plant stress responses, mediating a fine balance between oxidative damage and adaptive signaling. Precise regulation of ROS production and scavenging is essential for sustaining cellular homeostasis under drought, salinity, and temperature extremes. Advances in CRISPR/Cas-mediated editing of ROS-related genes, overexpression of antioxidant enzymes (e.g., SOD, APX, and CAT), and application of redox-active biostimulants have demonstrated significant improvements in plant resilience and yield stability under combined stresses. Future climate-smart breeding programs should integrate ROS-signaling markers, antioxidant enzyme profiles, and redox transcriptomic data to accelerate the development of stress-tolerant cultivars tailored for variable environments.