Figure 1.

Electron transport pathways operating during oxygenic photosynthesis and their role in ATP generation. LEF (blue solid arrow) operates from PSII to PSI and reduces NADP⁺ to NADPH using electrons from water. It also generates a pmf across the thylakoid membrane composed of a proton gradient (ΔpH) and electrical gradient (ΔΨ); the pmf is used by the ATPase to generate ATP (proton translocation is shown in red dashed lines; ATP fluxes are shown in red plain lines). CEF (light pink solid arrow) and PCEF (magenta solid arrow) both contribute to the generation of the pmf but do not produce reducing equivalents since the e⁻ used for PCEF reduces O₂ to water. CMEF (pink solid arrow) encompasses multiple metabolic pathways by which reductants generated in the chloroplast are shuttled to the mitochondria and converted into ATP by the mitochondrial electron transport chain. NADPH and ATP generated by these different pathways are eventually used for transforming CO₂ into biomass, which reflects net photosynthesis. AOX, alternative oxidase; CBB, Calvin–Benson–Bassham; FDX, ferredoxin; FLVs, flavodiiron proteins; FNR, ferredoxin-NADP⁺ reductase; Myxo, myxothiazol; PS, photosystem; PGR5/L1, PROTON GRADIENT REGULATION 5/like-1; SHAM, salicylhydroxamic acid; I, III, IV, respiratory complexes I, III, and IV.