Abstract
Plants are affected by numerous environmental factors that influence their physiological processes and productivity. Early revealing of their action based on measuring spectra of reflected light and calculating reflectance indices is an important stage in the protection of agricultural plants. Photochemical reflectance index (PRI) is a widely used parameter related to photosynthetic changes in plants under action of stressors. We developed a new system for proximal imaging of PRI based on using short pulses of measuring light detected simultaneously in green (530 nm) and yellow (570 nm) spectral bands. The system has several advances compared to those reported in literature. Active light illumination and subtraction of the ambient light allow for PRI measurements without periodic calibrations. Short duration of measuring pulses (18 ms) minimizes their influence on plants. Measurements in two spectral bands operated by separate cameras with aligned fields of visualization allow one to exclude mechanically switchable parts like filter wheels thus minimizing acquisition time and increasing durability of the setup. Absolute values of PRI and light-induced changes in PRI (ΔPRI) in pea leaves and changes of these parameters under action of light with different intensities, water shortage, and heating have been investigated using the developed setup. Changes in ΔPRI are shown to be more robust than the changes in the absolute value of PRI which is in a good agreement with our previous studies. Values of PRI and, especially, ΔPRI are strongly linearly related to the energy-dependent component of the non-photochemical quenching and can be potentially used for estimation of this component. Additionally, we demonstrate that the developed system can also measure fast changes in PRI (hundreds of milliseconds and seconds) under leaf illumination by the pulsed green-yellow measuring light. Thus, the developed system of proximal PRI imaging can be used for PRI measurements (including fast changes in PRI) and estimation of stressors-induced photosynthetic changes.
Highlights
Multi- and hyperspectral imaging is the widely-used basis of the sensing [1] allowing for quick measurements of changes in spectra of reflected light without physical contact with the object which are strongly related to numerous physiological processes including photosynthesis [2,3,4,5], water exchange [6,7], changes in contents of pigments [8,9,10,11,12,13], emission of plant volatiles, electrical signaling [16,17,18], responses on damages by phytopathogens [19,20,21], primary production [22], etc
Absolute value of Photochemical reflectance index (PRI) decreased with the AL intensity increase, but significant changes in PRI were only observed under light intensities equal to 210 and 280 μmol m−2 s−1 (Figure 4b)
Its efficiency was primarily evaluated with using pea seedlings in laboratory experiments
Summary
Multi- and hyperspectral imaging is the widely-used basis of the sensing [1] allowing for quick measurements of changes in spectra of reflected light without physical contact with the object which are strongly related to numerous physiological processes including photosynthesis [2,3,4,5], water exchange [6,7], changes in contents of pigments [8,9,10,11,12,13], emission of plant volatiles (e.g., isoprene emission [14,15]), electrical signaling [16,17,18], responses on damages by phytopathogens [19,20,21], primary production [22], etc. Calculation of reflectance indices based on measurements of the intensities of reflected light at specific wavelengths is a conventional way of analysis of multi- and hyperspectral data. The analysis can be based on complex investigation of all possible reflectance indices [15,26,27,28,29,30,31] which opens ways to search for new reflectance indices in plants
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