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

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-Sp d application during drought. Exogenous Spd exhibited higher FJ (fluorescence value at the J-step (2 ms) of OJIP) and FP (maximal recorded fluorescence intensity, at the peak P of OJIP) than non-Sp d application. Moreover, normalised total complementary area (Sm) and the number of QA (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 QB (secondary quinone acceptor of PS II) to PSI acceptors (delta R0), absorption flux per RC (ABS/RC) and trapping flux per RC (TR0/RC) compared to the non-Sp d 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.

Automated summary

The study found that exogenous Spd can significantly enhance the protection of photosynthetic apparatus in tall fescue under drought stress, promoting the functionality of the photosynthetic system. Compared to non-Spd application, Spd application decreased the values of electron transfer efficiency and specific energy flux.