A light-induced decrease in the photochemical reflectance index (PRI) can be used to estimate the energy-dependent component of non-photochemical quenching under heat stress and soil drought in pea, wheat, and pumpkin

The remote sensing of a plant's physiological state is a key problem of precision agriculture. The photochemical reflectance index (PRI), which is based on the intensities of the reflected light at 531 and 570 nm, is an important tool for the remote sensing of photosynthetic processes in plants. In particular, the PRI can be strongly connected with the non-photochemical quenching of chlorophyll fluorescence (NPQ) and the quantum yield of photosystem II (CYRILLIC CAPITAL LETTER EFPSII); however, this connection is dependent on illumination, the intensity of stressor actions, the time scale of measurements, etc. The aim of the present work was to analyze the connection of PRI with the energy-dependent component of NPQ (NPQ(F)) and CYRILLIC CAPITAL LETTER EFPSII under heating and soil drought conditions. Pea, wheat, and pumpkin seedlings, which were grown under controlled conditions, were investigated. A PAM fluorometer Dual-PAM-100 and spectrometer S-100 were used for measurements of photosynthetic parameters and PRI, respectively. It was shown that heat stress increased the NPQ(F) and the magnitude of light-induced changes in PRI (Delta PRI) and decreased CYRILLIC CAPITAL LETTER EFPSII in pea seedlings. The decreased CYRILLIC CAPITAL LETTER EFPSII and increased Delta PRI were observed in wheat after heating, but significant changes in NPQ(F) were absent; the significant decrease in CYRILLIC CAPITAL LETTER EFPSII was observed in pumpkin seedlings, while there were no significant changes in the other parameters. Delta PRI and NPQ(F) after heating were significantly correlated. However, a significant correlation of the absolute values of PRI with photosynthetic parameters was absent. The soil drought increased NPQ(F) and the magnitude of Delta PRI and decreased CYRILLIC CAPITAL LETTER EFPSII in peas. Delta PRI was strongly correlated with photosynthetic parameters, but this correlation was absent for the absolute value of PRI. Thus, Delta PRI is strongly connected with the magnitude of NPQ(F) and can be used as an estimator of this parameter.