Disequilibrium between chloroplast proton motive force and ATP levels in Arabidopsis

Current dogma holds that CO2 fixation by photosynthesis requires additional ATP production via PGR5-dependent cyclic electron transfer (PGR5-CET) to augment the NADPH and ATP produced by linear electron transfer (LET). Here we use the MgATP2- fluorescent biosensor ATeam1.03-nD/nA and find that while proton motive force (pmf) in the Arabidopsis pgr5CAS mutant is only 50-75% of that of the wild-type, MgATP2- levels are unchanged. These data demonstrate that disequilibrium exists between pmf and MgATP2- concentration in vivo, indicating that PGR5-CET is not required for ATP augmentation.