Biosynthesis and multifaceted roles of reactive species in plant defense mechanisms during environmental cues

• Elucidates ROS and RNS biosynthesis and their spatiotemporal signaling dynamics. • Reveals ROS-RNS crosstalk modulating plant immunity and abiotic stress adaptation. • Highlights advanced imaging for in vivo visualization of reactive species in plants. • Identifies gaps in molecular specificity of ROS/RNS signaling and gene regulation. • Integrates ROS/RNS roles with hormonal and epigenetic networks in stress resilience. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are key components of plant metabolism, acting as cellular damage agents and essential signalling molecules. They play crucial roles in plant growth, development, and responses to environmental cues. This review clarifies their distinct and overlapping functions within plant signalling pathways. ROS and RNS are produced in organelles such as chloroplasts, mitochondria, and peroxisomes, where their concentrations are tightly regulated to balance signalling functions and prevent cellular damage. We explore their signalling roles, mechanisms underlying signal transduction, interactions across plant systems, and influence on plant stress responses. Evidence shows that ROS and RNS regulate adaptation to drought, salinity, pathogens, and herbivores. Advanced imaging techniques have enhanced our understanding of their cellular dynamics in redox signalling pathways, highlighting the need to balance their production and scavenging for optimal plant health. Understanding their biosynthesis, signalling, and interactions is crucial for unravelling their contributions to plant growth and resilience.