THE CARBON DIOXIDE FACTOR 1895 



The observations on the shape of the carbon dioxide curves of Chlorella 

 remain contradictory. In table 27.1, two measurements were listed, one 

 by Warburg, showing half -saturation at 0.4 X 10 "-^ moIe/1. and a slow 

 approach to complete saturation somewhere above 7X10"^ mole/1. CO2 ; and 

 one by Emerson and Green, showing half-saturation at 0.35 X 10"^ mole/1, 

 and sharp saturation at 0.7 X 10"^ moIe/1. CO2. Osterlind (1950) pub- 

 lished curves for the rate of growth of Chlorella pyrenoidosa as a function of 

 [CO2], which showed half-saturation first at 2.5 X 10"^ mole/1, and full 

 saturation at 10 X 10"^ mole/1, (free carbon dioxide, at pB. 8). 



Whittingham (1952) made a new determination of the carbon dioxide 

 curve of Chlorella pyrenoidosa, in acid phosphate buffer (pH 4.6), using 

 saturating light. The method was similar to that of Emerson and Green 

 {i. e. the rate was measured as function of declining CO2 content in a closed 

 system), but the gas was circulated, and [CO2] was determined with a re- 

 cording infrared spectrometer. Eight points were measured between 

 1.0 and 0.04 X 10"^ mole/1. CO2 (table 37D.II), indicating half-saturation 

 as early as at 0.1 X 10"^ mole/1, and full saturation near 1 X 10"^ mole/1. 

 Whittingham's earlier measurements (1949) had indicated that, in car- 

 bonate buffer, the photosynthesis of Chlorella pyrenoidosa cultures ac- 

 climated to a medium of low CO2 content may be half-saturated at even 

 lower CO2 concentrations — as low as 0.05 X 10"^ mole/1! 



Table 37D.II 



P = /[CO2] OF Chlorella in the Steady State in Acid Buffer in Saturating Light 



(after Whittingham 1952) 



[C02],% 0.030 0.011 0.0089 0.0070 0.0052 0.0033 0.0017 0.0013 



" m./l. X 105 10 0.37 0.30 0.23 0.17 0.11 0.057 0.043 

 P 18.0 16.8 16.3 14.6 12.5 11.5 8.5 6.8 



Warburg and co-workers (1951) found a strong influence of free carbon 

 dioxide concentration on the maximum quantum yield, Tmax., of photo- 

 synthesis in Chlorella pyrenoidosa, as determined by the method of intermit- 

 tent illumination. The experimental points fell on the same T^ax. = 

 /[CO2] curve, whether determined in acid phosphate or in alkaline carbon- 

 ate medium {cf. fig. 37D.27). We will discuss these results in section 4 of 

 this chapter; what concerns us here is that Warburg's conclusions have 

 caused Emerson to re-investigate the fC02] dependence of photosynthesis 

 in Chlorella in weak, steady light. Table 37D.III shows the results, in acid 

 and alkaline media. No effect of [CO2] (or of pH) on the quantum require- 

 ment could be noted, between 0.2% (7 X 10"^ mole/1.) and 5% (16 X 

 10~^ mole/1.) free CO2, corresponding to pH values from 9.0 to 4.8. This 

 region has been generally known to be one of CO2 saturation in strong light, 



