Abiotic stress causes plants to create and store ROS in subcellular compartments. Oxidative stress from high ROS levels damages cells, disrupts membranes, and kills them. Cellular activity depends on antioxidant enzymes and detoxification processes to balance ROS generation and removal. By increasing antioxidant defenses and lowering oxidative damage, plant growth-promoting rhizobacteria (PGPRs) strengthen crops under stress. Their regulation of enzymatic and non-enzymatic antioxidants, including catalase, superoxide dismutase, ascorbate peroxidase, glutathione reductase, α-tocopherol, flavonoids, and phenolics, protects plants even under normal circumstances. Recent research on microorganisms in antioxidant defense and plant responses to drought, salt, temperature changes, and heavy metal exposure is discussed in this chapter.