Experimental evidence suggesting that H2O2 is produced within the thylakoid membrane in a reaction between plastoquinol and singlet oxygen

•Singlet oxygen oxidizes plastoquinol to plastoquinone.•Oxidation of plastoquinol by singlet oxygen produces hydrogen peroxide.•Hydrogen peroxide formation is stoichiometric with oxidation of plastoquinol.•Plastohydroquinone enhances the chemiluminescence of the luminol-peroxidase system. Plastoquinol (PQH2-9) and plastoquinone (PQ-9) mediate photosynthetic electron transfer. We isolated PQH2-9 from thylakoid membranes, purified it with HPLC, subjected the purified PQH2-9 to singlet oxygen (1O2) and analyzed the products. The main reaction of 1O2 with PQH2-9 in methanol was found to result in formation of PQ-9 and H2O2, and the amount of H2O2 produced was essentially the same as the amount of oxidized PQH2-9. Formation of H2O2 in the reaction between 1O2 and PQH2-9 may be an important source of H2O2 within the lipophilic thylakoid membrane.