Figure 3. Kinetics of proton motive force and photosynthetic acclimation on transition from dark to light.

(a) Kinetics of ECS_t (total electrochromic shift, a measure of total proton motive force size, PMF) in wild-type plants (wt), vccn1-1 knockout mutant and mutant overexpressing AtVCCN1 (oeVCCN1) were recorded at 650 μmol photons per m² per s after 30 min dark adaptation. (b) Fraction of PMF contributed by transmembrane electric-potential gradient (ΔΨ) and H⁺ concentration gradient (ΔpH) at two time points in the light. (c) H⁺ conductivity through ATP synthase (g_H⁺) was determined from ECS decay kinetics. (d) Kinetics for induction of non-photochemical quenching (NPQ) as a measure of photoprotective mechanisms were recorded during 10 min of illumination at 650 μmol photons per m² per s. (e) Photosystem II quantum yield (Φ_II) as a measure of linear electron transport was calculated from the same experiment as NPQ. Data are the means ±s.e.m. (n=5). Where not visible, error bars are smaller than the symbols. Asterisks denote a statistically significant difference between wt and mutants (Student's t-test, P<0.05).