Photo-Oxidative Stress in Plants: Molecular Mechanisms, Damage, and Adaptive Strategies for Resilience

Photo-oxidative stress results from an imbalance between light absorption and photosynthetic carbon utilization, posing a major threat to plant productivity and resilience under climate change. This review synthesizes recent advances in the molecular mechanisms of photo-oxidation, focusing on the dual role of reactive oxygen species (ROS) as both toxic byproducts and key signaling molecules. We outline the specific sites of ROS generation in chloroplasts, particularly singlet oxygen (¹O₂) at Photosystem II (PSII) and hydrogen peroxide (H₂O₂) at Photosystem I (PSI), and describe their distinct retrograde signaling pathways that regulate nuclear gene expression for acclimation. A systems perspective reveals how photo-oxidative damage propagates through interconnected cycles of impaired photosystem repair, lipid peroxidation, and protein oxidation, ultimately risking cellular collapse. To cope, plants employ a multi-layered photoprotective arsenal, including non-photochemical quenching (NPQ), alternative electron sinks, and integrated antioxidant networks. These mechanisms are further examined within an ecological and evolutionary context, highlighting natural variation and trade-offs between growth and defense. Finally, we discuss future directions for translating this knowledge into strategies for engineering climate-resilient crops, emphasizing the role of synthetic biology, multi-omics integration, and genomics-assisted breeding in supporting global food security.