Lag phase of CO2-dependent O-2 evolution by illuminated Anabaena variabilis cells

The steady-state rate of CO2-dependent O-2 evolution by Anabaena variabilis cells in response to illumination was established after a lag phase. The l ag 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 a bsent during electron transfer from H2O to p-benzoquinone (in combination w ith ferricyanide) involving Photosystem II. A lag was observed during elect ron transfer from H2O to methyl viologen involving Photosystems II and I, b ut not for electron transfer from N,N,N:N'-tetramethyl-p-phenylenediamine ( in combination with ascorbate) to methyl viologen involving only Photosyste m I. The lag phases of the light-induced H2O -> CO2 and H2O -> methyl violo gen electron transfer reactions showed the same temperature dependences at 10-30 degrees C. The lag was prevented by 3-(3,4-dichlorophenyl)-1,1-dimeth ylurea at concentrations that caused partial inhibition of photosynthetic O -2 evolution. Retardation of cell respiration by a combination of CN- and b enzylhydroxamate shortened the lag phase of the H2O -> methyl viologen elec tron transfer. It is concluded that the lag phase is associated with the el ectron transfer step between Photosystem II and Photosystem I common for th e photosynthetic and respiratory chains and is due to the stimulation of ce ll respiration during the initial period of illumination as a consequence o f an increase in the reduced plastoquinone pool and to subsequent retardati on of respiration resulting from the transition of the electron transfer ch ain to the competitive pathway involving Photosystem I.