Figure 1.

(A) Membrane potential changes induced by a saturating continuous illumination (ki_PSII ∼ 500 s⁻¹, ki_PSI ∼ 2000 s⁻¹). The leaf is submitted to cycles of 1.7 s of light and 6 min of dark. The amplitude of the absorption changes associated with the transfer of one charge across the membrane (one PSI turnover) is ΔI/I = 2.74 × 10⁻³ (arrow). This measurement has been performed under conditions where PSII is inactive (20 μM DCMU + 1 mM hydroxylamine). (B) Enlarged view of the kinetics of membrane potential changes at the time the light is switched off. Dashed lines S_L and S_D, slopes before and after switching off the light. (S_L − S_D) ∼0.32 s⁻¹, expressed in ΔI/I units/s.