189G 



KINETICS OF PHOTOSYNTHESIS 



CHAP. 37D 



and it was a priori unlikely that more carbon dioxide could be needed to 

 reach CO2 saturation in weak light, where the demand is smaller; but 

 Warburg's observations in intermittent light made it advisable to look for a 

 possible, even if unexpected, specific [CO2] dependence of photosynthesis 

 in weak light. The absolute values of the quantum requirements in table 

 37D.III (and 37D.I) will be discussed in Section 4. 



Table 37D.III 



Quantum Requirement of Chlorella in Relation to CO2 Concentration 



(after Emerson") 



Cd 643.8 m/i, 0.20 Meinstein 



per min. 

 Cd 643.8 mn + Hg 579 mp, 



0.29 iueinstein per niin. 



9.0 



9.5 



9.2 



9.6 



8.8 



8.9 



" Cf. Emerson and Whittingham (1953). 



>> Warburg's buffer No. 9. 



" Warburg's "new buffer," cf. section 4 below. 



In subsequent papers, Warburg and co-workers (1953, 1954) mentioned 

 that other Chlorella cultures did not show the same dependence of the yield 

 on [COo] as the culture described in the 1951 paper. 



Steemann-Nielsen (1952), discounting the measurements of Emerson and Green, 

 suggested that the Chlorella strain used by Whittingham (1949) might have been per- 

 meable to bicarbonate, or sensitive to changes in pH (which, in carbonate buffers, ac- 

 company changes in [CO2]), rather than to charges in CO2 concentration. He considered 

 Osterlind's growth measurements, showing CO2 saturation at 10 X 10"^ mole/1. CO2, 

 as the only rehable determination of the CO2 curve of Chlorella pyrenoidosa. However, 

 subsequent measurements of Whittingham (1952) have revealed no bicarbonate utiliza- 

 tion by his strain of Chlorella pyrenoidosa (at least not at [CO2] = 7 X 10"^ mole/1.). 

 Osterhnd's observations of a strong effect of pH on the growth of this species also have 

 not been confirmed by measurements of photosynthesis (e. g., those of Emerson and 

 Green, cf. p. 340), except at pH > 9. Furthermore, in Whittingham's measurements, a 

 detrimental effect of high pH should have accelerated — and not delayed — the decline of 

 the rate with increasing pH (since, in carbonate buffers, [CO2] is lower the higher pH). 

 The suggestions of Steemann-Nielsen are therefore insufficient to explain the discrepancy. 



Gaffron and Rosenberg {cf. Rosenberg 1954) also studied the dependence 

 of photosynthesis in Chlorella on carbon dioxide concentration, at various 

 light intensities, using a glass electrode. They employed either a sealed re- 

 action vessel, in which dilute bicarbonate solution was equilibrated with 

 CO2 gas of different pressure, or an open system, in which a gas stream, con- 

 taining 0.25-1.25% CO2, passed first through the reaction vessel (containing 



