Ultra-weak photon emission as a physiological indicator of stress: a study of mechanical injury response in Arabidopsis using bandpass filters

Abstract Ultra-weak photon emission (UPE) offers a non-invasive window into plant physiological states, particularly in response to adverse conditions. This study refines the spectral analysis of UPE in 7-week-old Arabidopsis thaliana plants subjected to mechanical injury, directly addressing well-documented detection challenges in the longer-wavelength regions and enhancing the utility of UPE as a biomarker for oxidative damage. Previous investigations utilized cut-on absorption filters and CCD imaging, which suffered from imprecise spectral resolution due to poor filter characteristics and reliance on subtraction methods for band emission computation. In contrast, our current study employs bandpass optical filters covering the 400–750 nm range in 50 nm increments, significantly improving the accuracy of UPE spectral data. We measured UPE kinetics after applying a standardized mechanical injury by sharp leaf incision. The study evaluates the suitability of these bandpass filters for discerning UPE spectral patterns in both spontaneous and induced emission scenarios in Arabidopsis leaves. It optimizes detection of crucial longer-wavelength emissions often indicative of reactive oxygen species (ROS) formation. Given that UPE intensity directly correlates with the rate and extent of ROS formation, monitoring these changes provides a robust, non-invasive means to assess oxidative metabolic states and internal responses. Our findings reveal that a significant increase in total UPE following mechanical injury occurs in the 700–750 nm spectral range (band B7), emerging as the dominant contributor to total UPE. Furthermore, our analysis indicates that UPE also includes a significant emission from the 750–870 band and presence in ultraviolet (UV) region. This research demonstrates that bandpass filters offer a accurate and reliable method for characterizing UPE photobiological responses of plants to mechanical injuries.