NITRATE REDUCTION 



453 



reduced and assimilated in connection with a respiratory breakdown of 

 carbohydrates, but the Ught intensity is insufficient for a quantitative 

 reassimilation of the extra carbon dioxide. This is given off, and it 

 exceeds in amount the apparent uptake of carbon dioxide in the photo- 

 synthesis; thus both carbon dioxide and oxygen are given off. It seems 

 Ukely that the gas exchange in the nitrate assimilation and photosynthe- 

 sis can actually proceed in this manner independently of each other 

 because the cells were supplied with 4 per cent carbon dioxide in the 

 air. This renders an increase in the carbon dioxide assimilation by the 



Table 8-1. Gas Exchange of Chlorella Cells Raised at Low and 



High Light Lntensities 

 (Computed from Myers, 1949.) 



Light, 

 ft-c 



Gas exchange 



O2 



CO2 



Extra gas 



O, 



CO., 



Real CO2 

 assimilation" 



Low-carbohydrate algae 



High-carbohydrate algae 



" For computation see text. , 



* Average values given for light of ft-c intensity. 



extra carbon dioxide produced highly improbable near the point of 

 compensation. 



In plants low in carbohydrates a fairly constant respiratory quotient 

 of about —0.80 was obtained, indicating, according to Myers, that the 

 reduction of nitrate closely follows the photosynthesis. This interpreta- 

 tion can justify an attempt to compute from Myers's data the assimi- 

 lation of carbon dioxide separated from the gas exchange caused by the 

 nitrate assimilation and the respiration. The formation of "extra gas," 

 according to Warburg, indicates the intensity of the nitrate assimilation 

 regardless of whether oxygen or carbon dioxide is given off in excess ; this 

 also follows from Eqs. (8-5a, b, c). Such figures have been computed in 

 Table 8-1, disregarding the fact that in the absence of nitrate the respira- 

 tory quotient does not equal exactly 1, an error that has to be neglected. 

 It is obvious that in both high- and low-carbohydrate plants this value 



