INFLUENCE OF OXYGEN ON INDUCTION 



1369 



reached a constant level in about 2 minutes. This type of induction curve 

 is correlated with the occurrence of sigmoid hght curves of steady photo- 

 synthesis; they occur more often in hydrogen than in nitrogen, and are 

 favored by carbon dioxide deficiency. 



With Chlorella, an even more pronounced second inhibition wave was 

 observed (fig. 33.18A) ; it led to a minimum of oxygen production between 

 0.5 and 1 minute after the beginning of illumination. The "secondary 

 induction loss" increases with the length of the dark period, although it 

 was noticeable after only 1 minute in darkness (subsequent to a previous 

 3 hour incubation). It is enhanced by low temperature — at 0° C. a deep 

 depression at 0.5 minute extended over as much as 4 minutes before the 



O 



O 



Q 

 O 

 CC 

 Q- 



O 



Secondary 

 wave 



Inverse 

 induction 



^Sfeody 

 level 



12 3 4 



■ TIME, min. 



Fig. 33.18B. Inverse induction in Scenedesmus in absence 

 of added CO2 after 3 hours in pure streaming N2 (after Shiau and 

 Franck 1947). 0° C, 12.5 X 10 -^ g. algae in 2.5 cc. 



oxygen production finally picked up. Poisoning by cyanide or extreme 

 carbon dioxide deficiency acts in a similar way. 



These experiments first showed that the "second wave" of induction 

 can affect also oxygen liberation. (It was previously observed only in 

 carbon dioxide consumption, and in fluorescence.) Franck, French and 

 Puck (1941) previously had suggested that the second wave may be caused 

 by a "blockade" of the chlorophyll surface by accumulated intermediate 

 oxidation products ("photoperoxides") not removed rapidly enough by the 

 inhibited "deoxygenase." Such a blockade could increase fluorescence 

 and prevent the uptake of carbon dioxide, but could not be expected to 

 cause a decline in the rate of oxygen production. An alternative explana- 

 tion of the second depression was therefore suggested by Shiau and Franck 

 (1947) (part B, section 2). 



When carbon dioxide was absent or, more exactly, when only the small 

 amount of carbon dioxide produced by fermentation was present, "inverse 



