A shift in chloroplast energy coupling by KCl from localized to bulk phase delocalized proton gradients

Spinach thylakoids were resuspended in a buffer including either 200 mM sucrose or 100 mM KCl. singleturnover flash excitation and the luciferin‐luciferase system were used to energize and follow ATP formation. The effect of the permeable buffer pyridine was measured on the ATP formation onset lag and on the post‐illumination ATP yield. Consistent with a bulk phase delocalized proton gradient coupling model, thylakoids stored in 100 mM KCl exhibited an increase in these two parameters in the presence of pyridine. Thylakoids isolated in the absence of KCl showed no effect of pyridine on the two parameters indicating a localized energy coupling mode.