The onset of photophosphorylation correlates with the rise in transmembrane electrochemical proton gradients.

The onset of photophosphorylation was determined by exposing chloroplast thylakoids to either single or multiple light flashes of varying duration. In aggreement with the results of Ort et al. (Ort, D.R., Dilley, R.A. and Good, N.E. (1976) Biochim. Biophys. Acta 449, 108--124), the permeant buffer imidazole in the presence of valinomycin and K+ did not greatly delay the onset of phosphorylation driven by multiple activation. In single flashes, however, the lag in the development of phosphorylation was much longer and imidazole caused a further delay. A significant delta pH was generated by the multiple flash regime. The onset of photophosphorylation is, therefore, consistent with the rise in transmembrane delta pH.