Prediction of respective contribution of linear electron flow and PGR5-dependent cyclic electron flow to non-photochemical quenching induction

In chloroplasts, regulated formation of the proton gradient across the thylakoid membrane (Delta pH) is important for controlling non-photochemical quenching (NPQ), which is crucial for plants to perform photosynthesis under fluctuating light conditions. The Delta pH is generated by two electron flows: the linear electron flow (LEF) and the cyclic electron flow (CEF). The Arabidopsis CEF mutant, pgr5, showed significantly lower NPQ values than those observed in WT, indicating that Delta pH, generated by the PGR5-dependent CEF, has a crucial role in controlling NPQ. However, the respective significance of LEF and CEF for Delta pH formation is largely unknown. Here we applied computer simulation to reproduce NPQ induction kinetics and estimate the respective contribution of LEF and PGR5-dependent CEF to the dynamics of Delta pH formation. The results indicate that the contribution of CEF to total Delta pH formation for induction of NPQ varies from 60-80%. The simulation also suggested a role of the PGR5-dependent CEF in accelerating electron transfer in the cytochrome bar complex. (C) 2014 Elsevier Masson SAS. All rights reserved.