1462 



PHOTOSYNTHESIS IN INTERMITTENT LIGHT 



CHAP. 34 



dark periods, for two different concentrations of carbon dioxide. The two 

 curves appear to retain an approximately constant ratio at all ta values and 

 not to approach a common limit — as we would expect if the maximum yield 

 per flash were equal (or equivalent) to the available amount of the finishing 

 catalyst, Eb. By using sufficiently intense flashes, it should be possible 

 to produce enough intermediates to put all molecules of Eb to work, even if 

 many of the absorbed quanta were lost because of the scarcity of carbon 

 dioxide-acceptor complexes. The flashes used in the experiments of 

 Emerson and Arnold were just strong enough to achieve flash saturation 

 in the presence of abundant carbon dioxide ; perhaps, no true saturation was 

 obtained in the carbon dioxide-deficient medium (despite the evidence 

 of the last two points on the curve) . With the usual flashing-light technique 

 (involving a long sequence of flashes) it is difficult to obtain flashes much 

 more intense than those used by Emerson and Arnold, to see whether the 

 two curves in figure 34.16 would converge at the higher intensities. 



Fig. 34.17. Induction in oxygen liberation by flashes after anaero- 

 bic incubation (after Franck, Pringsheim, and Lad 1945). 



We mentioned, however, that much higher intensities of single flashes 

 can be produced by exploding flash bulbs, as was done in the phosphores- 

 cence measurements of Franck, Pringsheim and Lad (1945). Two points, 

 however, have to be cleared before this method can be applied to the solu- 

 tion cf our problem. In the first place, the phosphorescence technique re- 

 quires absence of oxygen; under these conditions, the saturation yield in 

 steady light may be only 1% of the normal, aerobic value. Is then the 

 flash yield in the absence of air at all comparable with that obtained aero- 

 bically? The answer is that it is of the same order of magnitude, but may 

 be smaller by a factor of five or even ten (corresponding to Chlo/P = 10,000- 

 20,000, instead of the usual 2000). This shows that the poison that ac- 

 cumulates during anaerobic incubation has much less effect on maximum 

 yield per flash than on maximum yield in continuous light. This is con- 

 firmed by the observation that the maximum flash yield is independent of 

 the density of the algal suspension (which is decisive for the extent of 



