Light-dependent inhibitory action of p-nitrothiophenol on Photosystem II in relation to the redox state of electron carriers

Abstract

The photosystem-II activity of chloroplasts was inhibited by the treatment with p-nitrothiophenol (NphSH) in the light, and the inhibition was accompanied by a change of the fluorescence spectrum. Aromatic mercaptans examined were active in causing this inhibition and fluorescence change. These effects of p-nitrothiophenol were highly accelerated by blocking the electron transport on the oxidation side of photosystem II by carbonyl cyanide- m-chlorophenylhydrazone (CCCP) or Tris · HCl or heat pre-treatment, whereas these were suppressed by blocking the transport on the reduction side by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). It was deduced that the site of NphSH action in the electron transport chain is closer to the reaction center of photosystem II that the blocking site of CCCP or Tris · HCl or heat, and that such a site in photosystem II is exposed to be modified with NphSH when electron carriers on the oxidation side of photosystem II are oxidized by illumination.