CYANIDE INHIBITIOX OF PHOTOSYNTHESIS 



Table 12.11 



Inhibition of Photosynthesis (P) in Chlorella by Cyanide in the 



Region of the Compensation Point (after Warburg) 



Low [CO2] (4 X 10-^ m.A.), strong light, 10° C] R = respiration 



ZQ'A 



of the figures in table 12.III is negative — not even the value obtained 

 in 0.005 molar cyanide solution. 



Table 12.III 



Effect of HCN on Oxygen Liberation by Chlorella (after Warburg) 



[CO2] = 9.1 X 10-s m.fl., 25° C, 19,000 lux; P = - 30 to - 40 mm./h. 



Before discussing the interpretation of this interesting result, we shall 

 first describe the influence of cyanide on other algae. The results show 

 wide variations, both in the absolute sensitivity of the photosynthesizing 

 apparatus, and in the relative sensitivity of photosynthesis and respira- 

 tion. Van der Paauw (1930) found, for example, that the photosynthesis 

 of Hormidium flaccidum was stimulated by cyanide in concentrations up 

 to 2 X 10"-* m./l., and inhibited only above this concentration. The 

 effect of cyanide on photosynthesis was roughly equal to its effect on 

 respiration: no cyanide-resistant residual photosynthesis could be ob- 

 served. The inhibition was equally strong in intense and in weak light. 

 All these results differed from Warburg's observations on Chlorella. 

 Van der Paauw suggested that, in Hormidium, cyanide affects the 



