Impact of Salinity on the Energy Transfer between Pigment–Protein Complexes in Photosynthetic Apparatus, Functions of the Oxygen-Evolving Complex and Photochemical Activities of Photosystem II and Photosystem I in Two Paulownia Lines

The present study shows the effect of salinity on the functions of thylakoid membranes from two hybrid lines of Paulownia: Paulownia tomentosa x fortunei and Paulownia elongate x elongata, grown in a Hoagland solution with two NaCl concentrations (100 and 150 mM) and different exposure times (10 and 25 days). We observed inhibition of the photochemical activities of photosystem I (DCPIH(2) → MV) and photosystem II (H(2)O → BQ) only after the short treatment (10 days) with the higher NaCl concentration. Data also revealed alterations in the energy transfer between pigment–protein complexes (fluorescence emission ratios F(735)/F(685) and F(695/)F(685)), the kinetic parameters of the oxygen-evolving reactions (initial S(0)-S(1) state distribution, misses (α), double hits (β) and blocked centers (S(B))). Moreover, the experimental results showed that after prolonged treatment with NaCl Paulownia tomentosa x fortunei adapted to the higher concentration of NaCl (150 mM), while this concentration is lethal for Paulownia elongata x elongata. This study demonstrated the relationship between the salt-induced inhibition of the photochemistry of both photosystems and the salt-induced changes in the energy transfer between the pigment–protein complexes and the alterations in the Mn cluster of the oxygen-evolving complex under salt stress.