430 



II. GAFFRON 



starting photosynthesis is being superimposed. The sharp kink en- 

 countered in the majority of cases, particularly if followed by long 

 flat compensation periods, forces us to assume a strong direct inter- 

 ference of the photochemical process with the respiratory metabolism. 

 We should not forget that what we see here is related only to the 

 carbon dioxide side of the picture, but there is no reason for assuming 

 that the absorption of oxygen should become blocked in the light, 

 as is the case with certain purple bacteria. Our experimental conditions 

 are similar enough to those maintained in Brackett and Olson's ex- 

 periments and in those of A. Brown to be quite sure that our algae 



Fig. 7. Enlarged part of recording of Fig. 6 at pH 6.8. Dark time between heavy 

 vertical lines 2 minutes. Transients after "light off" last about 1 minute, are prob- 

 ably caused by three superimposed reactions: (i) "Pick up" = Cj -|- C,; (^) "back 

 reaction" = decarboxylation of dicarboxylic acid; (3) normal respiration. 



continue to take up respiratory oxygen in the light. It is the release of 

 respiratory carbon dioxide which is stopped or exactly compensated 

 the moment the light strikes the cells. And occasionally this com- 

 pensation reaction takes precedence over the normal photosynthetic 

 one for times lasting up to a minute or even more. In other words 

 respiratory intermediates are being reduced while the Benson-Calvin 

 cycle is still inactive. 



A corresponding effect is nearly always found when the light is 

 turned off. After the carboxylation reaction — which is known to con- 

 tinue for a few seconds in the dark — has subsided, one sees a flat por- 

 tion in the curve, indicating that respiration is not yet leading to a 

 net release of carbon dioxide; in other words an oxidation of reduced 



