Paraquat Affects Light-Induced Proton Transport Through Chloroplast Membranes in Spinach

Abstract

Listen

Translate article

In both oxidative phosphorylation and photo-phosphorylation, electron flow through a carrier is linked to the generation of ATP. The energy released by electron transport is converted to potential energy forming a proton gradient across the membranes in chloroplasts and that is coupled to ADP phosphorylation. In this report, a method is used to study effects of paraquat on proton movement across the chloroplast membranes. Paraquat is a bipyridyl herbicide and its salt is used as a biological oxidation-reduction indicator. Light-induced proton transport through chloroplast thylakoids is affected by the presence of paraquat. The proton uptake upon illumination and proton leakage in the dark were enhanced at a low paraquat concentration (< 20 nM). The rate of proton uptake by the illuminated thylakoids followed the first order of kinetics. However, paraquat gradually reduces proton transport with the increase of the herbicide concentration. The pH at the steady state in the illuminated thylakoid membranes becomes more acidic with the elevation of the herbicide concentration. The method is useful in the study of the toxic effect of herbicides on the fundamental process of photosynthesis.