INTERACTION OF THE ELECTRON-DONOR DIPHENYLCARBAZIDE WITH THE HERBICIDE-BINDING NICHE OF PHOTOSYSTEM-II

In experiments using thylakoid membranes, it was found that the inhibitory action of atrazine and 3-(3,4-dichlorophenyl)-1, 1-dimethylurea is weaker in the presence of the Photosystem II electron donor sym-diphenylcarbazide. The concentration dependences of sym-diphenylcarbazide for electron donation and the relief of inhibition by the herbicides were different, higher concentrations being required for the latter. These data could not be explained by the electron donation properties of sym-diphenylcarbazide. Instead, the donor was shown to displace [C-14]atrazine from its binding site. The photoreduction of 2,5-dichlorobenzoquinone, monitored using oxygen evolution experiments, was also strongly reduced in the presence of sym-diphenylcarbazide. A direct interaction of sym-diphenyl-carbazide with the herbicide-binding niche is demonstrated.