Inhibition by Tetranitromethane of Photosynthetic Electron Transport from W ater to Photosystem II in Chloroplasts

Tetranitromethane, Inhibition of Photosynthesis, Oxygen Evolution, Photosystem II Low concentrations (10 /xM) of tetranitromethane inhibit noncyclic electron transport in spinach chloroplasts. A study of different partial electron transport reactions shows that tetranitromethane primarily interferes with the electron flow from water to PS II. At higher concentrations the oxida­ tion of plastohydroquinone is also inhibited. Because diphenyl carbazide but not Mn2+ ions can donate electrons efficiently to PS II in the presence of tetranitromethane it is suggested that it blocks the donor side of PS II prior to donation of electrons by diphenyl carbazide. The pH de­ pendence of the inhibition by this protein modifying reagent may indicate that a functional-SH group is essential for a protein, which mediates electron transport between the water splitting complex and the reaction center of PS II.