412 



George Hoch and Olga v. H. Owens 



comitant decrease 

 change is very mu 

 that the cyaniae 

 the light. Cyani 

 sis to about cornp 

 tion of the photo 

 are being inhibit 

 the failure of cy 

 to other inhibito 



in oxygen uptake so that the net gas ex- 

 ch less. Also evident in the figure is 

 effect is somewhat progressive with time in 

 de at 10~.5m, while inhibiting photosynthe- 

 ensation, is actually allowing recornbina- 

 products, so that the light reactions per se 

 ed only slightly. This perhaps explains 

 anide to cause fluorescence changes similar 

 rs of photosynthesis ^'^, 



As the cyanide concentration is increased (to lO'^M) both 

 oxygen production and uptake go to zero. Although the 

 effects of cyanide appear complex the light dependent uptake 

 of oxygen is only indirectly affected by cyanide. The drop 

 in rate of light uptake results from the action of cyanide 

 on the oxygen production mechanism, Vi/hich in turn brings 

 about a lowered production of the oxidizable reductant. 



An investigation was made of the effect of cyanide at 

 lower light intensities at wavelengths where either one or 

 the other of the two photosystems predominates. Figure 3 

 shov/s such an experim.ent with Scenedesmus . The controls 



50 



RATE 

 IN 40 



CELL VOLS/HR 



O2 PROD. 



O2 

 UPTAKE 



-20. 



20 



40 



60 



80 



100 



INTENSITY 



-2 



_i L 



+ CN- 



CONTROL 

 J 1 I t I L. 



20 



40 



60 



80 



INTENSITY 



100 



show the typical response which we have found at two wave- 

 lengths. Vi'hen the light is saturating, as shown in the 

 higher intensities of 65O light, the cyanide effect is 

 large, inhibiting photosynthesis to ^Oyo. At lower intensi- 

 ties, on the linear part of the curves, the cyanide effect 



