570 



PHOTOSYNTHESIS AND RESPIRATION 



CHAP. 20 



poisoning below the compensation point; and even though this result is 

 controversial (c/. page 309), it certainly is true that it has been impossible 

 to stifle photosynthesis completely by cyanide without using such 

 concentrations of the poison which would affect respiration as well. 



Gaffron (1937, 1939) had more success with the reverse procedure — 

 quenching the respiration of Scenedesmus, without damaging photosyn- 

 thesis. Typical results are shown in Table 20. III. The fact that "true 



Table 20.III 



Effect of Cyanide on Respieation and Photosynthesis in Scenedesmus 

 (0.09 ml. cells in phosphate buffer, pH 5.9, 21° C; air with 5% CO2) 



photosynthesis," calculated in the last line of table 20. Ill by the sub- 

 traction of dark respiration from the net gas exchange in light, remains 

 practically constant, while respiration itself drops to 4% of its original 

 value, can be considered as an indication that respiration in light is the 

 same as in the dark. (Strictly speaking, the constancy of the figures in 

 the last row proves only that the difference Ri — Rdis independent of cy- 

 anide concentration; it is feasible, but improbable that this difference is 

 constant, but not zero.) 



Although none of the experiments described above provides a final 

 proof of the nonexistence of true "photorespiration," the least that can 

 be stated is that no evidence of such a phenomenon has as yet been 

 found (except perhaps in ultraviolet light), and that all definitely estab- 

 lished cases of light-stimulated respiration were of the "persistent" 

 type, and could be attributed either to an accumulation of sugars or to 

 an indirect photochemical effect of blue-violet light absorbed by the 

 carotenoids. 



Bibliography to Chapter 20 



Photosynthesis and Respiration 



1881 Borodin, I., Mem. acad. sci. St. Petersbourg, VIII, 28, No. 4. 



1893 Palladin, W., Commun. Univ. Kharkov, 1893. Cf. Botan. Zentr., 58, 



375, 1894. 

 1919 Warburg, 0., Biochem. Z., 100, 230. 

 1922 Warburg, 0., and Negelein, E., Z. physik. Chem., 102, 235. 





