Figure 1. Efficiency of electrons extraction for three quinone derivatives in the ΔpetA strain lacking the cytochrome b₆f complex.

The steady-state fluorescence yield (F_S) was measured after ∼2.6 s of illumination at 26 μmol photons m⁻² s⁻¹, while the maximum fluorescence (F_M) was measured after a saturating light pulse (250 ms). Variations in (F_M−F_S)/F_M values, related to the PSII photochemical efficiency, were used to estimate the efficiency of electrons extraction (mean±s.d.; n=3). The restoration of PSII photochemical efficiency in the ΔpetA strain by the exogenous quinones indicates their ability to act as electron acceptors. The empty circle and the dashed line show the (F_M−F_S)/F_M value in the WT reference strain in the absence of exogenous quinones under the same light condition (mean±s.d.; n=10).