Inactivation of photosynthetic oxygen evolution by o-phenanthroline and LiClO4 in Photosystem 2 of the pea

We examined the effects of o-phenanthroline and LiClO₄ on oxygen evolution and electron transport in the Photosystem 2 complex of the pea. Treatment of Photosystem 2 particles with a combination of 3.0 mM o-phenanthroline and 1.0 M LiClO₄ for 30–40 min at 0°C decreased the oxygen-evolving activity with the electron acceptor (either phenyl-p-benzoquinone or 2,6-dichlorophenol indophenol) to less than 5% of the original level. However with the same treatment, the electron-transport activity from an artificial electron donor, 1,5-diphenylcarbohydrazide, to 2,6-dichlorophenol indophenol remained at 60% of the original activity. The amount of manganese in the Photosystem 2 complex decreased in parallel with the loss of oxygen evolution following treatment. These observations suggest that the treatment of the Photosystem 2 complex with o-phenanthroline and LiClO₄ inhibits electron transport on the oxygen-evolving side much more significantly than on the electron-acceptor side.Abbreviations Chl chlorophyll - DCPIP 2,6-dichlorophenol indophenol - DPC 1,5-diphenylcarbo hydrazide - EDTA ethylenediaminetetraacetic acid - Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - Mes 4-morpholineethanesulfonic acid - PBQ phenyl-p-benzoquinone - PS 2 Photosystem 2