Harmonious Operation of PSII Efficiency and Antioxidant Activity is Decisive for Salt Tolerance in Barley Genotypes

In this study, the effect of salt stress (120 mM NaCl for 7 d) on some physiological changes was investigated through chlorophyll a fluorescence technique, JIP test, and some endogenous resistance mechanisms (activity of some antioxidant enzymes and free proline content) in two barley cultivars (Hordeum vulgare L. cvs. Erginel-90 and Tokak 157/37). Chlorophyll fluorescence measurements and the calculated JIP test parameters showed that salt stress did not damage PSII reaction centers in both barley cultivars but reduced the rate of electron transport reactions from reaction centers to the plastoquinone pool in the genotype Erginel-90. Moreover, changes in ΔRo and ФRo confirmed that electron transport in the genotype Erginel-90 was also reduced further than plastoquinone. In the genotype Tokak 157/37, however, photosynthetic electron transport reactions were maintained under salt stress conditions. Contrary to the genotype Tokak 157/37, the impairment in the photosynthetic efficiency led to oxidative stress in the leaf tissues of the genotype Erginel-90 under salt stress. This fact was confirmed by the lower foliar antioxidant activity, accumulation of H₂O₂ and malondialdehyde, and thus photooxidative damages in the photosynthetic pigments. These results allowed us to conclude that the photosynthetic apparatus of the genotype Tokak 157/37 is more tolerant to salt stress than the genotype Erginel-90. In addition, ΔV/Δto, S_M, N, Ψo, Ψo/(1 – Ψo), PI_ABS, ФRo, and ΔRo could be considered decisive and informative JIP test parameters to evaluate salt tolerance in barley plants.