Application of chlorophyll fluorescence in the assessment of environmental stresses in crops.

Introduction: Plants in the environment are affected by various stresses, depending on the duration, intensity and growth stage of the plant, these stresses can reduce the process of photosynthesis and affect their growth and performance. However, traditional methods, even technically advanced ones such as the measurements of photosynthetic rates through the gas exchange (CO₂, H₂O, and O₂), are timeconsuming and provide incomplete information on overall photosynthetic function. The development of knowledge in the field of chlorophyll fluorescence shows that this indicator has a high ability to study the photochemical efficiency of plant photosynthesis. Methods: For measuring the chlorophyll fluorescence in plants, leaves were dark-adapted for 30 minutes using leaf clips provided by the producer of handy-PEA. Measurements were performed on the middle of plant leaves following the standard protocol with illumination with continuous red light (peak in 650 nm wavelength; the spectral line half-width of 22 nm) provided by an array of three light-emitting diodes. The light pulse intensity used was 3500 μmol(photon).m^-2s^-1 and the duration of the light pulse was 1 s. The measured data were used for the calculation of the photosynthetic parameters using Biolyzer v. 3.06 HP software (a software provided with handy-PEA). Some of the parameters we discussed in this article due to their significance are F_O = minimum fluorescence, F_M = maximum fluorescence, F_O/F_M = The maximum quantum yield of basal non-photochemical energy losses, F_V/F_M = the maximum quantum efficiency of PSII, VJ = the relative variable fluorescence in step J after 2 ms, VI = the relative variable fluorescence in step I after 30 ms, N = the number of QA redox turnovers until FM, SM = the pool size of the electron acceptors on the reducing side of PSII, PIABS = performance index. Main Findings: The study of chlorophyll fluorescence can analyze with high detail the function and state of PSII reaction centres, and light-harvesting complexes. This index has a high correlation with other physiological parameters under different environmental stresses. In this article, an overview of the results of chlorophyll fluorescence analysis of crops underenvironmental stressesis given, and the key steps to stresses are presented. Under drought stress the ratio of active reaction centers in chlorophyll, primary photochemical reactions, and electron transfer are affected. By salinity stress in crops, the values of variable and, maximum fluorescence, the energy required to close the reaction centers, and the photosynthetic efficiency index decrease, while the time required to reach the maximum fluorescence increases. Under cold stress conditions, electron transfer flow per reactive centers, the quantum performance of photosystem II, and the efficiency of the water splitting complex in photosystem II decrease. Potassium affects light-dependent steps such as the size of receiving antennae and the electron connection of photosystem II reaction centers. The electron acceptor part of photosystem II is the main site of inhibition of photosynthetic electron transfer under the application of herbicides. Conclusion and Implications: This article has provided an overview of the information about the wide opportunities of using the chlorophyll fluorescence technique in plant science, agriculture and ecological research. The measured parameters of chlorophyll fluorescence are called the JIP-test and its analysis can be used to evaluate the effects of environmental stresses on plants. This technique requires more practical studies in biotic and even non-biotic stress conditions to provide reliable information to investigate the growth and development of plants, and this leads to an increase in our knowledge of the physiological basis of crop photosynthesis under stress conditions. [ABSTRACT FROM AUTHOR]