[Inhibition of electron transport and photophosphorylation in chloroplasts by quercetin].

The influence of quercetin on electron transport and photophosphorylation of pea isolated chloroplasts with methylviologen and NADP+ has been studied. Quercetin inhibits ATP synthesis and phosphorylating electron transport but does not affect the basal electron transport in the presence of methylviologen. In view of these data and because of the increase of the proton uptake by chloroplasts in the presence of quercetin we consider it as an inhibitor of energy transfer. Under conditions of NADP+ photoreduction quercetin acts also as an inhibitor of electron transfer, interacting with ferredoxin, though a complete inhibition of electron transfer has not been observed. This last phenomenon may be of importance for the understanding of the detailed mechanism of NADP+ reduction by chloroplasts.