Inhibition of Photosystem II in the Green Alga <i>Ankistrodesmus falcatus</i> by Copper

Abstract

Abstract Copper strongly inhibited 2,6‐dichloroindophenol (DCIP) photoreduction in the broken cells of the green alga Ankistrodesmus falcatus (C303), and the activity lost could not be restored by adding 1,5‐diphenylearbazide (DPC). Inactivation of the DCIP Hill reaction reached 45% after incubation with 10 μ M cupric sulfate for 20 min. In the same time, copper (13 μg/mg chlorophyll) was bound to the broken cells. Addition of 10 m M KCl reduced copper binding by about 53%. Fluorescence intensity at room temperature decreased upon addition of cupric sulfate and was partially restored by adding 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), These results suggest that copper inactivates electron transport between the oxidizing side of the reaction center of photosystem II and the electron‐donating site of DPC. Further, the effect of light intensity shows that copper mostly affected the reaction rate of the dark step and had less inhibitory effect on the quantum efficiency of the primary reaction of electron transport in photosystem II.