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

Abstract

The present study shows the effect of salinity on the functions of thylakoid membranes from two hybrid lines of <i>Paulownia</i>: <i>Paulownia tomentosa</i> x <i>fortunei</i> and <i>Paulownia elongate</i> x <i>elongata</i>, 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 (DCPIH₂ → MV) and photosystem II (H₂O → 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 F₇₃₅/F₆₈₅ and F_695/F₆₈₅), the kinetic parameters of the oxygen-evolving reactions (initial S₀-S₁ state distribution, misses (α), double hits (β) and blocked centers (S_B)). Moreover, the experimental results showed that after prolonged treatment with NaCl <i>Paulownia tomentosa</i> x <i>fortunei</i> adapted to the higher concentration of NaCl (150 mM), while this concentration is lethal for <i>Paulownia elongata</i> x <i>elongata</i>. 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.