1366 



INDUCTION PHENOMENA 



CHAP. 33 



metabolism of a general diffusible, acidic and reducing inhibitor, are those 

 of Noack, Pirson and Michels (1939) and Michels (1940). They observed 

 that neutralization of the medium as well as aeration can remove the anaero- 

 bic inhibition, sometimes almost instantaneously. This is illustrated by 



6 

 E 



o 

 < 



o Bicarbonate buffer, Nj 



+ Culture medium, pH 4, 

 Nz +C02, 25° C 



■*••'-*■— H— t-- 



-»*-+-*—* 



120 240 360 480 



TIME AFTER BEGINNING OF ILLUMINATION, min 



c 

 o 



o 



CO 



< 



o 



in 

 a. 



8- 



Culture medium, pH 4, 25° C. 

 o Quinone 

 + Air 



l^:a>.v 



120 



240 



360 



TIME AFTER BEGINNING OF 

 ILLUMINATION, min. 



Fig. 33.17. (a) Induction in Chlorella after 13.5 hours of anaerobiosis in acid or 

 alkaline medium, (b) Quinone added after 60 minutes light, or air bubbled through 

 solution 60-105 minutes after beginning of illumination (after Noack, Pirson and Mich- 

 els 1939). 



figure 33.17, which shows the practically complete inhibition of photosyn- 

 thesis of Chlorella by 13.5 hours of anaerobiosis in an acid nutrient solu- 

 tion, and the absence of a similar effect in an alkaline buffer. Figure 33.17b 

 shows that the inhibition can be removed by aeration in the dark (in the 

 course of which a considerable quantity of oxygen is taken up by the cells), 

 and, even more rapidly, by the addition of quinone. The chemical nature 

 of the easily oxidizable, acid fermentation products indicated by Noack's 

 experiments is as yet imknown. Assays were made for lactic acid but it 

 was found in only relatively small quantity (in agreement with Gaffron's 

 observations on Scenedesmus; cf. chapter 6, page 138). 



