1460 



PHOTOSYNTHESIS IN INTERMITTENT LIGHT 



CHAP. 34 



catalyst, P"'^''- = (/cea/w)Eb, is assumed to be considerably lower than 

 the "ceiling" imposed by the A-C02-supplying capacity of the carboxylase, 

 kE\. In flashing light, the average yield, under the conditions of Eb 

 limitation, is (/cea/w) [Er], where [Eb] designates the average amount of 

 actively engaged catalyst Eb- If the flash intervals are > Iea, this rate can 

 also be expressed as NEb, where N is the number of flashes per second 

 (sixteen in our example). In the poisoned state, on the other hand, the 

 rate Umitation is given by the rate of supply of the substrate by the 

 residual carboxylase, kEl. This applies to continuous light as well as to 

 regular flashes. (Of course, the final products are liberated in the second 

 case in bursts following each flash, as indicated by the peaked curves; 

 but the total volume of these bursts is limited by the intake of carbon di- 

 oxide, which goes on uniformly.) With grouped flashes, however, the 

 EA-liniitation remains practically ineffective even in the inhibited state 

 (since, in this case, the "ceihng" A;Ea = 0.43 mm.Vmin. is considerably 

 higher than the [Eb ]-determined rate, 0.33 mm.Vmin.). The experiments 

 mth flash groups provide the most convincing argument against the hy- 

 pothesis of "substrate limitation" as an alternative to "hmitation by a finish- 

 ing catalyst." 



4. Influence of Temperature, Carbon Dioxide Concentration, Narcotics 



and Ultraviolet Light on Flash Yield 



Emerson and Arnold (1932^ found that decrease in temperature, though 

 increasing required dark time, leaves P"'''" unaffected; fig. 34.14 shows 



I 

 < 



a: 



LU 

 Q. 



Q 



_i 



UJ 



>- 

 llJ 

 > 



I- 

 < 



_l 



a: 



600 



500 



400- 



300 



200 



100 



QI6 



^ Q02 0.04 006 008 QIO 012 014 

 DARK TIME, sec. 



Fig. 34.14. Yield per flash curves for low and high 

 temperature (after Weller and Franck 1941). 



confirmation of this conclusion by Weller and Franck (1941). This result 

 appears natural, since lower temperature leaves unaffected both the quan- 

 tity of the intermediates available after a flash, and the quantity of the 



