The Influence of Soil Salt Stress on Modified Photochemical Reflectance Indices in Pea Plants

Abstract

Salinization is a significant adverse factor that suppresses productivity of agricultural plants. Multispectral imaging and calculation of reflectance indices, including the typical photochemical reflectance index (PRI), can be used for early revealing of changes in plants under salinization. However, the direction of change in typical PRI is dependent on the type of stressor and the experimental conditions. Earlier, we proposed modified PRIs with shifted measuring wavelengths and analyzed their changes under excess light, water deficit, and heating. In the current work, we investigated the sensitivity of these indices to changes in pea plants under salinization (100, 200, and 400 mM NaCl treatment). It was shown that short-wavelength PRIs were increased under this treatment; in contrast, long-wavelength PRIs were decreased. Most of the modified PRIs were strongly related to the maximal yield of photosystem II and the normalized difference vegetation index. Long-wavelength PRIs were more sensitive to plant changes than short-wavelength PRIs, typical PRI, and the normalized difference vegetation index because their stable decrease under moderate salinization (the 200 mM NaCl treatment) was initiated earlier. Our results show that long-wavelength PRIs, which also decreased under the action of the excess light, water deficit, and heating, can be potentially used as a universal tool for early revealing of stress changes in plants.