Hydrogen Peroxide Inhibits Photosynthetic Electron Transport in Cells of Cyanobacteria

V. D. Samuilov^*, D. B. Bezryadnov, M. V. Gusev, A. V. Kitashov, and T. A. Fedorenko

Department of Cell Physiology and Immunology, School of Biology, Lomonosov Moscow State University, Moscow, 119899 Russia; fax: (095) 939-3807; E-mail: vds@8.cellimm.bio.msu.ru

^* To whom correspondence should be addressed.

Received October 9, 2000

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The effect of H₂O₂ on photosynthetic O₂ evolution and photosynthetic electron transfer in cells of cyanobacteria Anabaena variabilis and Anacystis nidulans was studied. The following experiments were performed: 1) directly testing the effect of exogenous H₂O₂; 2) testing the effect of intracellular H₂O₂ generated with the use of methyl viologen (MV); 3) testing the effect of inhibiting intracellular H₂O₂ decomposition by salicylic acid (SA) and 3-amino-1,2,4-triazole (AT). H₂O₂ inhibited photosynthetic O₂ evolution and light-induced reduction of p-benzoquinone (BQ) + ferricyanide (FeCy) in the Hill reaction. The I₅₀ value for H₂O₂ was ~0.75 mM. Photosynthetic electron transfer in the cells treated with H₂O₂ was not maintained by H₂O₂, NH₂OH, 1,5-diphenylcarbazide, tetraphenylboron, or butylated hydroxytoluene added as artificial electron donors for Photosystem (PS) II. The H₂O --> CO₂, H₂O --> MV (involving PSII and PSI) and H₂O --> BQ + FeCy (chiefly dependent on PSII) electron transfer reactions were inhibited upon incubation of the cells with MV, SA, or AT. The N,N,N´,N´-tetramethyl-p-phenylenediamine --> MV (chiefly dependent on PSI) electron transfer was inhibited by SA and AT but was resistant to MV. The results show that H₂O₂ inhibits photosynthetic electron transfer. It is unlikely that H₂O₂ could be a physiological electron donor in oxygenic photosynthesis.

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KEY WORDS: photosynthesis, photosynthetic oxygen, water-oxidizing complex, Photosystem II, Photosystem I, hydrogen peroxide, cyanobacteria, Anabaena variabilis, Anacystis nidulans

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