Abstract
Light quality is a key environmental signal that integrates plant immune pathways, yet how specific wavelengths regulate the execution, timing, and efficiency of the hypersensitive response (HR) remains incompletely resolved. This study investigated how light spectral composition modulates HR dynamics and resistance outcomes during a non-host interaction. Tobacco leaves were inoculated with Pseudomonas syringae pv. tomato DC3000 (PstDC3000) and incubated under red (RL), green (GL), blue (BL), white light (WL), or darkness. Monochromatic light treatments distinctly reshaped HR progression. BL and WL induced rapid HR characterized by early accumulation of reactive oxygen species (ROS), accelerated electrolyte leakage, and pronounced callose deposition. RL and GL delayed visible HR while effectively restricting bacterial proliferation by moderating ROS production, delaying membrane disruption, and sustaining cell wall reinforcement. In darkness, ROS accumulation was dysregulated, tissue collapse was uncontrolled, and pathogen growth was not effectively constrained. These results demonstrate that light wavelength fine-tunes HR kinetics and qualitatively distinct defense outcomes, with RL and GL favoring controlled immune responses over rapid cell death. By identifying GL as a key modulator of regulated immunity, this study provides a conceptual framework for managing light environments to optimize plant disease resistance.