Inhibition of electron flow and energy transduction in isolated spinach chloroplasts by the herbicide dinoseb

Abstract

The mode of action of dinoseb (2-sec-butyl-4-6-dinitrophenol) on chloroplast reactions was studied. Electron flow from water or from an artificial electron donor, diphenylcarbazide (DPC), to dichlorophenol indophenol (DCPIP) was inhibited at low concentrations of the herbicide (5–10 μM) suggesting a site for dinoseb inhibition at the oxidizing side of photosystem II (PS II). Ferricyanide photoreduction was also inhibited by dinoseb. Cyclic and non-cyclic photophosphorylation and Mg 2+-ATPase activity were inhibited by dinoseb, which indicates that this herbicide also acts as an energy transfer inhibitor. Among the above mentioned activities, non-cyclic photophosphorylation was the most sensitive to the inhibition by dinoseb. Ca 2+-ATPase activity of solubilized heat activated chloroplast coupling factor 1 (CF 1) was stimulated by dinoseb. However, the same activity was inhibited in chloroplasts, which perhaps reflect a difference in the mode of interaction of dinoseb with solubilized and membrane bound coupling factor.