1424 



INDUCTION PHENOMENA 



CHAP. 33 



enhances the second wave and delays its decay practically indefinitely (c/. 

 fig. 33.39). 



We cannot recount here all the details of Franck's interpretation, by 

 means of this induction theory, of all the variations in the shape of gas 

 exchange and fluorescence-time curves uncovered in the experimental 

 studies reported in parts A and B of this chapter. One general surmise of 

 Franck should, however, be emphasized. He believes that the production 

 of a "blanket" of a narcotizing metabolite on the surface of chlorophyll 

 (and perhaps also on the surface of some catalysts) must be an important 



12 3 4 



TIME, sec. 

 Fig. 33.51. Time course of concentration variation of two 

 narcotics and their total concentration, which influences fluo- 

 rescence intensity of chlorophyll (after Shiau and Franck 1947): 

 (a) external inhibition; (6) internal inhibition. 



protective device developed by the plants to prevent destructive photo- 

 chemical reactions (such as photoxidations) from being sensitized by chloro- 

 phyll when photosynthesis is inhibited (for any possible reason). 



The peculiarities of the induction phenomena after anaerobic conditions 

 were explained by Franck, Pringsheim and Lad by the assumption of the 

 combined action of an "external" and the above introduced "internal" in- 

 hibitor. The "external" inliibitor is the repeatedly mentioned diffusible 

 acid and reducing material produced by fermentative metabolism and ex- 

 creted into the medium. This material accounts for the effect of alkalies on 

 anaerobic inhibition (Noack et al.), the importance of algal concentration 

 (Franck, Pringsheim and Lad), the immediate high fluorescence yield at the 

 beginning of illumination after prolonged anaerobic incubation, and many 

 other characteristics of anaerobic induction. Variations in the premeabil- 

 ity of cell membranes may play an important role in the inhibition phe- 

 nomena caused by this factor, particularly in the different sensitivity of 

 young and aged cells. 



