Measurements of Photochemical Reflectance Index as a Tool for Remote Monitoring of Photosynthetic Parameters of Plants

Developing remote and proximal sensing techniques to detect the early photosynthetic responses in stress conditions is of importance for agriculture and ecology. The photochemical reflectance index (PRI), which is typically calculated from the reflected light intensities at 531 and 570 nm, is potentially sensitive to rapid changes in photosynthesis under unfavorable conditions. Mechanisms of changes in PRI are thought to include chloroplast shrinkage, aggregation of light-harvesting complexes, transitions in the xanthophyll cycle, and changes in chlorophyll and carotenoid concentrations. This renders it difficult to employ PRI difficult in monitoring plant health. Use of pulsed light for measurements, study of the light-induced changes in PRI, and analysis of modified PRIs provide means to improve the efficiency of PRI applications. Other means (e.g., developing methods to estimate PRI on the basis of RGB imaging) are also impossible to exclude. Improving techniques to measure and analyze PRI holds significant promise for monitoring the photosynthetic responses of plants to environmental stress factors.