Lag Phase of CO₂-Dependent O₂ Evolution by Illuminated Anabaena variabilis Cells

V. D. Samuilov^* and T. A. Fedorenko

Department of Cell Physiology and Immunology, School of Biology, Lomonosov Moscow State University, Moscow, 119899 Russia; fax: (095) 939-3807

^* To whom correspondence should be addressed.

Received December 19, 1998

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The steady-state rate of CO₂-dependent O₂ evolution by Anabaena variabilis cells in response to illumination was established after a lag phase. The lag phase was shortened (1) in cells incubated with glucose as an oxidizable substrate and (2) upon an increase in light intensity. The lag phase was absent during electron transfer from H₂O to p-benzoquinone (in combination with ferricyanide) involving Photosystem II. A lag was observed during electron transfer from H₂O to methyl viologen involving Photosystems II and I, but not for electron transfer from N,N,N',N'-tetramethyl-p-phenylenediamine (in combination with ascorbate) to methyl viologen involving only Photosystem I. The lag phases of the light-induced H₂O --> CO₂ and H₂O --> methyl viologen electron transfer reactions showed the same temperature dependences at 10-30°C. The lag was prevented by 3-(3,4-dichlorophenyl)-1,1-dimethylurea at concentrations that caused partial inhibition of photosynthetic O₂ evolution. Retardation of cell respiration by a combination of CN^- and benzylhydroxamate shortened the lag phase of the H₂O --> methyl viologen electron transfer. It is concluded that the lag phase is associated with the electron transfer step between Photosystem II and Photosystem I common for the photosynthetic and respiratory chains and is due to the stimulation of cell respiration during the initial period of illumination as a consequence of an increase in the reduced plastoquinone pool and to subsequent retardation of respiration resulting from the transition of the electron transfer chain to the competitive pathway involving Photosystem I.

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KEY WORDS: photosynthesis and respiration, O₂ evolution, lag phase, b₆f complex, plastocyanin, Photosystem I, cyanobacteria, Anabaena variabilis

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