In this study, we characterized how lipid peroxidation alters the functionality of spinach thylakoids exposed to peroxyl radicals generated by the azo compound 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH). Incubation of thylakoids in presence of different concentrations (0 to 200 mM) of AAPH inhibited the formation of ΔpH (IC50 ≈ 1.5 mM) estimated by the quenching of 9-aminoacridine fluorescence (Q9-AA). The Q9-AA inhibition was correlated (R2=0.98) to the extent of lipid peroxidation determined by the accumulation of thiobarbituric acid reactive substances (TBARS). Much higher AAPH concentrations were required to inhibit the maximum (Fv/Fm) and effective (ΔF/Fm’) photochemical efficiencies of photosystem II (IC50 ≈ 120 mM and 50 mM respectively), indicating that moderate lipid peroxidation caused the uncoupling of spinach thylakoids. This was confirmed by the 62 % stimulation of the O2 uptake rates measured without the artificial uncoupler NH4Cl when the AAPH concentrations increased from 0 to at 20 mM, reaching similar values to the rates measured in presence of NH4Cl. Above 20 mM AAPH, the O2 uptake rates measured with and without NH4Cl declined similarly to the decrease of ΔF/Fm’. These results suggest that the increased H+-leakiness of thylakoid membranes could be one of the primary effects of oxidative stress.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.