Effects of copper chloride on photosynthetic electron transport and chlorophyll-protein complexes of Spinacia oleracea

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Incubation of class II spinach chloroplasts with Cu(II) caused inhibition of the rate of photosynthetic electron transport. The Cu(II) inhibition of the 2,6-dichlorophenol indophenol (DPIP)-Hill reaction (photosystem II) was restored by Mn(II) when phosphate buffer (pH 7.8) was used, but Mn(II) had no effect when N-2-hydroxyethylpipera-zine-N-2-ethanesulfonic acid buffer (pH 7.8) was used. The action of Mn(II) was to restore the oxygen evolving capacity, rather than to donate electrons to photosystem II. Cu(II) at a low concentration slightly stimulated the rate of overall electron transport from water to NADP, but the pattern of inhibition of higher Cu(II) concentrations was similar to the inhibition of DPIP reduction. The Cu(II) stimulation of whole chain electron transport was probably due to Cu(II) functioning as an uncoupler of photophosphorylation at low concentrations. In the presence of ascorbate (ASC) the addition of Cu(II) caused very rapid inactivation of the photosystem I reaction from Asc/DPIP to NADP. At the same time we also observed the rapid destruction of chlorophyll and chlorophyll-protein complexes both in light and in the dark. The underlying mechanism for the Cu (II) inhibition of photosystem I and the destruction of the chlorophyll-protein complexes, may be caused by the formation of H_2O_2 in a Cu(II) catalyzed autooxidation of ascorbate.
日本植物生理学会の論文