Disequilibrium between chloroplast proton motive force and ATP levels in Arabidopsis.

Current dogma holds that CO2 fixation by photosynthesis requires additional ATP production via cyclic electron transfer, mediated by two distinct pathways involving the NADH dehydrogenase-like complex (NDH) and proton gradient regulation 5 protein (PGR5), to augment the ATP relative to NADPH produced by linear electron transfer. Here we use the MgATP2- fluorescent biosensor ATeam1.03-nD/nA and find that, while proton motive force in the Arabidopsis pgr5CAS and pgr5 ndho mutants is only 50-75% that of the wild type, chloroplast MgATP2- levels are unchanged. These data demonstrate that disequilibrium exists between the proton motive force and MgATP2- concentration in vivo, indicating that cyclic electron transfer is not required for ATP augmentation.