title: Proton equilibration in the chloroplast modulates multiphasic kinetics of nonphotochemical quenching of fluorescence in plants.
abstract: In plants, the major route for dissipating excess light is the nonphotochemical quenching of absorbed light (NPQ), which is associated with thylakoid lumen acidification. Our data offer an interpretation for the complex relationship between changes in luminal pH and the NPQ response. Upon steady-state illumination, fast NPQ relaxation in the dark reflects the equilibration between the electrochemical proton gradient established in the light and the cellular ATP/ADP+Pi ratio. This is followed by a slower phase, which reflects the decay of the proton motive force at equilibrium, due to gradual cellular ATP consumption. In transient conditions, a sustained lag appears in both quenching onset and relaxation, which is modulated by the size of the antenna complexes of photosystem II and by cyclic electron flow around photosystem I. We propose that this phenomenon reflects the signature of protonation of specific domains in the antenna and of slow H(+) diffusion in the different domains of the chloroplast.
authors.affiliation: Institut de Biologie Physico-Chimique, Unité Mixte de Recherche 7141, Centre National de la Recherche Scientifique and Université Pierre et Marie Curie-Université Paris 6, 75005 Paris, France. pierre.joliot@ibpc.fr
authors.forename: Pierre A
authors.initials: PA
authors.lastname: Joliot
authors.forename: Giovanni
authors.initials: G
authors.lastname: Finazzi
mesh_terms: D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism; D005453:Fluorescence; D007700:Kinetics; D008027:Light; D045331:Photosystem I Protein Complex / Q000235:genetics; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism; D010944:Plants / Q000235:genetics / Q000378:metabolism; D018892:Proton-Motive Force / Q000235:genetics; D011522:Protons
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D011522:Protons