期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1974
卷号：71
期号：4
页码：1484-1488
DOI：10.1073/pnas.71.4.1484
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Ion movements associated with the pH rise that is observed upon illumination of thylakoid suspensions at low pH have been studied by a multiparameter technique. Light-dependent, dark-reversible fluxes of H+, Cl-, Na+, K+ and divalent cations were monitored, together with simultaneous changes in the optical density of the suspension. Extensive uptake of Cl- and efflux of Mg2+ accompany the apparent inward movement of H+ in the light. Only minor efflux of K+ is seen and Na+ appears immobile. The Cl- and Mg2+ fluxes together compensate for most of the charge transferred as H+, contributing respectively about 49% and 43% on an equivalent basis. The ratio of Cl- influx to Mg2+ efflux is variable, but usually >1.0. The Mg2+ flux can be supplanted by (1) K+ flux, if the K+/Mg2+ activity ratio in the suspension is high, and (2) Ca2+ flux, if the thylakoids are equilibrated with suspending media containing Ca2+. The affinity of the divalentcation-binding sites, or carrier mechanism, is greater for Ca2+ than for Mg2+. Schemes can be drawn up to account for the observed ion movements on the basis of either a chemical or a chemiosmotic mechanism for energy transduction in chloroplasts. In intact chloroplasts, light-dependent control of Mg2+ distribution between thylakoid and stroma could serve to regulate enzyme activities in the carbon fixation pathway, and hence photosynthesis.
