Effects of exogenous 24-epibrassinolide on the photosynthetic membranes under non-stress conditions

• EBR enhances the photosystem II photochemistry and electron-transport rate in pea thylakoid membranes.
• EBR changes the kinetics of oxygen evolution and decreases the ratio of functionally active PSIIα to PSIIβ centers.
• EBR induces alterations in the thermodynamic parameters of photosynthetic membranes.
• EBR causes reorganization of the main pigment–protein complexes and partial unstacking of thylakoid membranes.

In the present work the effects of exogenous 24-epibrassinolide (EBR) on functional and structural characteristics of the thylakoid membranes under non-stress conditions were evaluated 48 h after spraying of pea plants with different concentrations of EBR (0.01, 0.1 and 1.0 mg.L−1). The results show that the application of 0.1 mg.L−1 EBR has the most pronounced effect on the studied characteristics of the photosynthetic membranes. The observed changes in 540 nm light scattering and in the calorimetric transitions suggest alterations in the structural organization of the thylakoid membranes after EBR treatment, which in turn influence the kinetics of oxygen evolution, accelerate the electron transport rate, increase the effective quantum yield of photosystem II and the photochemical quenching. The EBR-induced changes in the photosynthetic membranes are most probably involved in the stress tolerance of plants.