222 H. TAMIYA, S. MIYACHI, T. HIROKAWA 



and the oxygen does not compete with quinone in their action as the 

 Hill reagent (6) (because R reacts with quinone preferably to oxy- 

 gen, and, therefore, there is little chance for the formation of H2O2). 



6. In normal photosynthesis (occurring under the condition of 

 light and CO2 saturation), existence of O2 does not lead to the forma- 

 tion of H2O2 detectable by the trapping method using catalase and 

 ethanol (because, under the said condition, not only is catalase 

 actively functioning, but also R has a stronger reactivity toward 

 CO2 than toward O2) . 



7. When oxygen acts as a Hill reagent, intermediate formation of 

 H2O2 is detected by the trapping method, and on trapping of H2O2 

 there occurs a positive O2 uptake, which does not occur — irrespective 

 of the presence or absence of cyanide— when H2O2 is not trapped 

 (c/. reactions (I), (II), (HI), and (VI)). Along the line of our reason- 

 ing mentioned under (e), it is deduced that both the stationary level 

 of R in the light and the process of its decay in the dark will vary in a 

 wide range according as the kind of reactant existing in the medium. 

 The state of affairs may give us a clue to the understanding of the 

 following facts : 



8. Whereas the induction period in the formation of R (in the 

 absence of CO2 and exogenous O2) lasts as long as 20 to 30 minutes 

 (see Fig. 1), the induction period occurring in normal photosynthesis 

 (in the presence of sufficient quantity of CO2) is of much shorter 

 duration (2 or 3 minutes) . 



9. In the absence of CO2 and of exogenous O2, the decay of R in 

 the dark occurs with a half-life of about 2 minutes, whereas the dark 

 C^* incorporation after a period of steady-state photosynthesis in 

 the presence of CO2 decays much faster (with a half-life of only 3 

 seconds; Gaffrone^aZ. (5)). 



10. In the Hill reaction occurring in the presence of quinone, 

 practically no induction period is observable. 



The role of catalase in the mechanism of photosynthesis has 

 long been a point of dispute among investigators of photosynthesis. 

 As we have sho^\Ti, cyanide not only inhibits the reaction between R 

 and CO2 but also accelerates the decay of R. The latter effect we 

 attribute to the reaction of R with H2O2 which we assume to derive 

 from the reaction between R and O2 (endogenous or exogenous) and 

 is left undecomposed if catalase is inhibited by cyanide. Since the re- 



