title: Catechols stimulate ferricyanide reduction in chloroplast photosystem II.
abstract: In isolated chloroplasts (Spinacia olearacea), where electron transport to Photosystem I is blocked by the plastoquinone antagonist, dibromothymoquinone, lipophilic catechols in concentrations of 50--150 microM stimulate ferricyanide reduction in Photosystem II and associated O2 evolution. Non-permeating catechols, such as Tiron, are unable to stimulate this reaction. Those quinones, such as 2,5-dimethylbenzoquinone, which act as class III electron acceptors, do not lead to stimulation of ferricyanide reduction in Photosystem II or stimulation fo associatied O2 evolution, when electron transport to Photosystem I is blocked by dibromoquinone. Stimulation of ferricyanide reduction is not observed in Tris-treated chloroplasts, implying that electron donation to Photosystem II by catechols is not responsible for the stimulation. Various mechanisms for this stimulation in class II chloroplasts are discussed.
mesh_terms: D002396:Catechols / Q000494:pharmacology*; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism*; D003374:Coumarins / Q000494:pharmacology; D005292:Ferricyanides / Q000378:metabolism*; D007700:Kinetics; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000187:drug effects*; D010944:Plants; D011794:Quercetin / Q000494:pharmacology; D013329:Structure-Activity Relationship
chemical_list: D002396:Catechols; D003374:Coumarins; D005292:Ferricyanides; D011794:Quercetin