Figure 2. Summary of chloroplast redox regulation in response to light availability.

Under low irradiance, electrons flow to NADPH, the NTRC is activated and reduces target enzymes. Under high irradiance, reduced ferredoxin (Fd_red) is oxidized by the FTR and Trx reduces target enzymes. In the dark, reduced target enzymes are reoxidized by a cascade involving thioredoxin L2 (TrxL2) and 2 Cys-peroxiredoxins (2CP) and a final transfer of electrons to H₂O₂. PSII, photosystem II; cytb₆f, cytochrome b₆f complex; PSI, photosystem I; Fd_ox, oxidized ferredoxin.