Catechols stimulate ferricyanide reduction in chloroplast Photosystem II

Abstract

In isolated chloroplasts (Spinacia oleracea), where electron transport to Photosystem I is blocked by the plastoquinone antagonist, dibromothymoquinone, lipophilic catechols in concentrations of 50-150 μM 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 of associated 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. © 1979.