365 



'W/M 



Kouchkovsky et al. 



v///////////////^w////w//77r 



Fig. 2. Schematic representation of typical curves obtainedwith 

 the "oxygen membrane electrode" (chloroplasts without Hill 

 reagent). 



: light; ////// : dark. Abscissa : time; 



ordinate : oxygen concentration. See text for explanation of symbols . 



A number of parameters defined in Fig. 2 serve to describe our experi- 

 mental curves. The following parameters, or functions thereof, were useful 

 in further analysis of our findings: 



A/tA = rate of the endoabsorption; 



B/tg = initial rate of the burst; 



C/tQ = steady-state rate of the photoabsorption; 



D = amount of oxygen evolved during the burst, as sunning photo- 



absorption starts only after the end of the burst; 



E = annount of oxygen evolved during the burst, assuming photo- 



absorption starts with the beginning of illumination (although this 

 assumption may not be strictly correct, E is a better measure 

 than is D; E was hence used for the quantitative estimations); 



F/tp = initial rate of the extra-absorption, calculated w^ith the endo- 

 absorption as reference; 



G/tQ = initial rate of the extra-absorption, calculated with the photo- 

 absorption as reference. 



According to Mehler and Brown' ', both evolution and consumption of 

 oxygen occur during photoabsorption. Then F/tp will measure the rate of 

 oxygen uptake and G/tQ the rate of oxygen evolution in the steady-state. 



