ROLE OF RESPIRATION IN INDUCTION PHENOMENA 



1423 



tion substrate is high, and, after a few minutes of illumination, drops to a 

 steady value (curve a in fig. 33.50A), the fluorescence (which depends on 

 the ratio [narcotic]/ [reducible substance]), represented by curve c, will first 

 follow curve a and then go over to curve b (fig. 33.50B), the transition 

 being as indicated by the dotted curve. 



Whether this "second wave" of narcotization of chlorophyll will cause, 

 in addition to a fluorescence wave, simultaneous inhibition waves in the 

 uptake of carbon dioxide and the liberation of oxygen, may depend on 



TIME, min. 



Fig. 33.50. Explanation of the second wave by competition of reducible substances 

 and inhibitor for chlorophyll (after Shiau and Franck 1947): (A) concentration vari- 

 ation of narcotics (b), of photosynthetically reducible substances (a) and of their ratio; 

 (B) theoretical fluorescence-time curves at two concentrations of photosensitive re- 

 ducible substance, with transition curve shown as broken hne. 



whether these rates, at the moment when the narcotization wave appears, 

 are limited by the amount of photochemically active chlorophyll, or the 

 amount of active catalyst Eb- This may explain why during the second 

 wave the usual antiparallelism between gas exchange and fluorescence is 

 found often, but not always. 



According to this interpretation of the second wave, it should be en- 

 hanced by all the factors that tend to depress the concentration of the re- 

 duction substrate, [A-COa], such as low carbon dioxide concentration, 

 low temperature and cyanide poisoning. This is confirmed by many ex- 

 perimental curves, although the results obtained with variable [CO2] seem 

 to be ambiguous (c/. p. 1339, 1381, 1391). Cyanide, in particular, clearly 



