In thylakoids system II water-splitting proton generation is mainly localized in grana stacks, whereas system I plastoquinol reoxidation, is essentially restricted to non-appressed regions, such as stromal lamellae; the same is true for the coupling factor. For a given mean proton gradient, a system II chain was found to be less able to drive phosphorylation than a system I or a system I + II chain. These results support our microchemiosmotic hypothesis, based on the existence of lateral resistances to H+ movements. They confirm that the proton gradients at the redox chain and at the coupling factor are unequal and that both are different from their mean experimentally measured value.
