FLUORESCENCE-TIME CURVES 1405 



large extent, to the accumulation of an acidic, reducing, fermentation 

 product, this inhibitor could be removed by oxidation with oxygen or 

 other oxidants, or by neutraUzation. 



Kautsky and Zedhtz (1941) noted that the fiuorescence-time curves 

 of grana precipitates could be changed from the anaerobic type to the 

 aerobic type either by aeration or by the addition of ferric oxalate or qui- 

 none. (Whether these two oxidants are especially useful, because of their 

 capacity to serve as oxidants in the "Hill reaction" of isolated or broken 

 chloroplasts, remains to be seen.) 



Shiau and Franck (1947) investigated the effect of quinone or alkali on 

 the fluorescence-time curves of Chlorella and Scenedesmus. In young 

 healthy cultures they found no effect, in either air or nitrogen, except after 

 12 hours of anaeroboisis. After such long anaerobic incubation, the addi- 

 tion of 10 ~' M quinone caused the induction to disappear and the steady 

 state value of (p to drop considerably. Quinone still had an effect on <p 

 even 15 minutes after the cells were exposed to air, showing the slowness 

 of recovery after extensive anaerobic pretreatment. Alkali caused, after 

 the same anaerobic pretreatment, first a transient increase and then a drop 

 in fluorescence. o-PhenanthroUne (10 ~* to 10 ~^ M) was found to counter- 

 act the effect of quinone addition. 



The same investigators also observed the effect of quinone and of al- 

 kalies on the fluorescence of isolated chloroplasts. The final fluorescence 

 intensity was reduced, by 10 ~* M quinone, about 10% below the initial 

 value, and the "wave" of (p in the first second disappeared completely. 

 Addition of 0.1 M potassium phosphate to a 12% sucrose solution (which 

 changed the pH from 6 to about 7.5) produced a similar effect. The ef- 

 fect of alkalies on chloroplasts was slower than that of quinone, and had a 

 high temperature coefficient (e. g., no effect was observed in 2 hours at 

 0°); it was more rapid with ions of smaller radius (Na). The neutrali- 

 zation effect was very fast and independent of temperature in disrupted 

 chloroplasts. With chloroplasts, o-phenanthroline had an effect similar 

 to that of the alkalies, rather than an antagonistic effect, as in live algae. 



The figures given in this chapter are but a small selection of the be- 

 wildering multitude of induction curves of gas exchange and fluorescence 

 available in the literature. They are probably enough to create the im- 

 pression of a field full of confusion and contradictions. However, we will 

 see below that, in the main, the results are capable of a not-too-complex 

 interpretation, based on the assumption of a twofold inhibiting effect: 

 a fast deactivation of the oxygen-liberating enzyme system in the dark, 

 and a relatively slow accumulation of surface-active inhibitors ("nar- 

 cotics") as a result of dark, particularly anaerobic, metabolism. 



