FLUORESCENCE-TIME CURVES 



1399 



(/) Oxygen; Effects of Anaerohiosis 



Since Kautsky believed, at first, that fluorescence quenching by oxygen, 

 converting the latter to a metastable form, is the first step in photosynthe- 

 sis several of his papers were devoted to the study of the influence of oxy- 

 gen on fluorescence during the induction period. However, the only defi- 

 nite result, obtained in the very first investigation (Kautsky, Hu'sch and 

 Davidshofer 1932), was that changes in the concentration of oxygen be- 

 tween 5 and 100% have no marked effect on the fluorescence-time curves. 



Fluorescence 



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Fig 33.43. Induction behavior of wheat under low (broken 

 Une) and under normal 02 pressure (after McAUster and Myers 

 1940): 0.03% CO2, high light, after 30 min. dark rest. 



In chapter 24, we noted that an increase of oxygen concentration from 

 0.5 to 20% resulted in a certain decrease of steady fluorescence, probably 

 related to the inhibiting effect of oxygen on photosynthesis. However, 

 McAlister and Myers (1940) found that, during the induction period, not 

 only fluorescence, but photosynthesis as well, were somewhat higher m 

 nitrogen than in air (fig. 33.43). The explanation is uncertam, but we 

 may recaU that inhibition of photosynthesis by excess oxygen requires 

 time (c/. chapter 19, fig. 60), and therefore may be absent m the first min- 

 utes of mumination. In other words, during the induction period, the 

 quenching of chlorophyll fluorescence by oxygen {of. chapt. 23, section Ab) 

 may be the main influence, while in the steady state the predominant eflect 

 is that due to the photoxidative inhibition of photosynthesis. In any case, 



the effect is small. , 



This result destroyed the original theory of Kautsky, and caused tne 



