Exogenously spermidine alleviates damage from drought stress in the photosystem II of tall fescue

Abstract

Drought stress is one of the major limiting factors to crop productivity around the globe. It has been well documented that spermidine (Spd) plays an important key role in plant growth and development, especially in the defense response to stress. The objective of this study was to explore the effect of Spd on protecting photosynthetic apparatus in tall fescue under drought stress. Spd application significantly improved the OJIP (fluorescence rise kinetics O-J-I-P) curve compared to non-Spd application during drought. Exogenous Spd exhibited higher F<sub>J</sub> (fluorescence value at the J-step (2 ms) of OJIP) and F<sub>P</sub> (maximal recorded fluorescence intensity, at the peak P of OJIP) than non-Spd application. Moreover, normalised total complementary area (S<sub>m</sub>) and the number of Q<sub>A</sub> (primary quinone acceptor of PS II) reduction events (N) significantly reduced after the application of Spd in tall fescue under drought stress. In terms of quantum yields and efficiencies and specific energy fluxes, exogenous Spd notably decreased the values of efficiency of electron transfer from Q<sub>B</sub> (secondary quinone acceptor of PS II) to PSI acceptors (δR<sub>0</sub>), absorption flux per RC (ABS/RC) and trapping flux per RC (TR<sub>0</sub>/RC) compared to the non-Spd application without watering. All the above suggested that exogenous Spd facilitated the photosynthetic system of tall fescue in drought. These observations involved in the electron transport capacity of photosystem II assist in understanding better the protective role of exogenous Spd in tall fescue under drought stress.