FLUORESCENCE INDUCTION PHENOMENA 



1377 



and Emerson and Lewis. Anaerobic incubation accentuates tiie ordinary 

 inhibition and, in addition, produces a second inhibiting factor that requires 

 no photochemical activation. 



(The above summary was based on the assumption that the normal 

 course of induction consists of a brief burst of uninhibited — but not en- 

 hanced — gas exchange, followed by one main wave, and sometimes one or 

 more secondary, waves, of inhibition; and that the only additional, uni- 

 lateral effect superimposed on this standard sequence is the Emerson-Lewis 

 carbon dioxide burst. More recent studies have shown that the true pic- 

 ture is more complex. In particular, the burst of oxygen liberation and 



TIME, min. 



Fig. 33.19a. Course of fluorescence 

 and photosynthesis in wheat during 

 induction period (after McAhster and 

 Myers 1940). Broken Unes show CO2 

 absorption curve corrected for slow 

 response of the apparatus. 



TIME, mm 



Fig. 33.19b. Fluorescence vs. time curves 

 at 23° C. of Hydrangea; excitation by 400- 

 600 m/i (after Franck, French and Puck 

 1941): (a) first half minute; (b) first 6 sec. 



carbon dioxide consumption in the first few seconds (or first minute) of 

 illumination may appear larger than could be produced by uninhibited, 

 steady photosynthesis during this brief period, and therefore seems to in- 

 volve (similarly to the carbon dioxide burst) a sudden photochemical trans- 

 formation (deoxygenation, carboxylation, decarboxylation) of some ma- 

 terial or materials accumulated in the cell during the dark period. The 

 following discussion of the induction effects in fluorescence was written 

 with the simpler picture of a few years ago in mind. Li particular, it con- 

 tains many references to "inhibition of photosynthesis" during certain in- 

 duction phases, while we would now prefer to speak more specifically of 

 inhibition of oxygen hberation, or inhibition of carbon dioxide uptake, or of 

 both together, if this be the case, rather than of inhibition of photosynthesis 

 as a whole.) 



