Non-Photochemical Quenching of Chlorophyll a Fluorescence as an Indicator of the State of a Plant Photosynthetic Apparatus Under Abiotic Stress

The parameters of chlorophyll a (Chl a) fluorescence of the primary leaves of 7-day-old barley sprouts under the impact of elevated temperature (40°C, 3 h) and water deficit (45 h in 3% PEG 6000) were studied. The potential and effective quantum yields of photochemical reactions of photosystem II and the photochemical (qP) and non-photochemical quenching (qN) of Chl a fluorescence were shown not to change significantly under these stress factors. High stress sensitivity was found for the coefficient of energy-dependent quenching of Chl a fluorescence (qE) related linearly with the magnitude of the H+ gradient across the thylakoid membrane. Because the qE value is an integral indicator dependent on the light and dark photosynthetic reactions, it was proposed to use this parameter as a marker of the stress state in the photosynthetic apparatus.