Fig. 2

ECS, de-epoxidation index, NPQ and chlorophylls bleaching of S4 strain compared to WT. a Proton motive force (pmf) obtained by electrochromic shift measurement (ECS) on whole cells at 1000 µmol photons m⁻² s⁻¹ and normalized to chlorophylls content. b De-epoxidation index of WT and S4 strains upon exposure to high light (2500 µmol photons m⁻² s⁻¹) for 1 h. Pigment composition was evaluated at different time points by HPLC analysis and de-epoxidation index was calculated as (zeaxanthin + antheraxanthin/2) /(antheraxanthin + violaxanthin + zeaxanthin). c Non-photochemical quenching (NPQ) induction of WT and S4 mutant strain at actinic light of 1500 µmol photons m⁻² s⁻¹. After 10 min of illumination actinic light was turned off to induce NPQ relaxation. d Chlorophylls bleaching kinetics: absorption of chlorophylls was measured for about 14 h upon exposure of cells to 2500 µmol photons m⁻² s⁻¹. Experimental data were fitted with linear function. Error bars are reported as standard deviation (n = 3). Significant different values are marked with ** as determined by unpaired two-sample t-test (n = 3, p < 0.01)