Complementary Roles of Chloroplast Cyclic Electron Transport and Mitochondrial Alternative Oxidase to Ensure Photosynthetic Performance

(A) The photosynthetic electron transport chain in chloroplast thylakoid membrane. Linear electron transport (LET) involves both photosystems while cyclic electron transport (CET) involves only photosystem I (PSI). Both modes of electron transport contribute to the proton motive force used by chloroplast ATP synthase (cATP synthase) to generate ATP, while only LET contributes to NADPH production. ATP and NADPH support carbon fixation by the Calvin-Benson (CB) cycle. One pathway of CET involves the proton-pumping NADH dehydrogenase-like (NDH) complex, while the other pathway involves the proteins PROTON GRADIENT REGULATION5 (PGR5) and PGR5-LIKE PHOTOSYNTHETIC PHENOTYPE1 (PGRL1). The malate valve can transfer NADPH equivalents from the stroma to cytosol. (B) The respiratory electron transport chain in inner mitochondrial membrane (IMM). Complex I, a family of other internal and external alternative dehydrogenases (NDin and NDex, respectively), and Complex II oxidize reducing equivalents. Electrons partition between the cytochrome (cyt) pathway [involving Complex III, cyt c, and Complex IV (cyt c oxidase)] and alternative oxidase (AOX). The proton motive force generated by electron transport is used by the mitochondrial ATP synthase (Complex V) to generate ATP. The proton gradient can also be dissipated by uncoupling proteins (UCP). Electron flow from reducing equivalents to cyt c oxidase is more tightly coupled to the generation of proton motive force (2–3 sites of proton translocation) than is electron flow from reducing equivalents to AOX (0–1 sites of proton translocation). Fd, ferredoxin; IMS, intermembrane space; and PC, plastocyanin.

Publication

The Complementary Roles of Chloroplast Cyclic Electron Transport and Mitochondrial Alternative Oxidase to Ensure Photosynthetic Performance. (2021) Avesh Chadee, et al. Front Plant Sci. 2021;12:748204. Figure: F1. All organisms Drosophila melanogaster Homo sapiens

Disease mentions