QUANTUM YIELD 



1943 



that such damaged cells regain full efficiency after several hours of strong 

 shaking (a treatment earlier described by Warburg as injurious!). 



Quantum requirements of 3-5 quanta per molecule oxygen were found 

 in these experiments with dense suspensions, low light intensities, and 

 bright intervals of 5, 10 or 15 min. However, induction periods of con- 

 siderable duration were observed, both in light and in dark, making cal- 

 culations uncertain. With not totally absorbing suspensions, stronger 

 light had to be used ; the quantum requirement was somewhat higher, and 

 showed a dependence on intensity and duration of illumination. 



7 Z 3 V 5 S 7 



Fig. 37D.26. Same as in fig. 37D.25, but without background light (after 

 Warburg and Geleick 1951). Quantum requirement in successive light period: 

 4..3, 4.3-5.2, 3.3-3.6; photosynthesis quotients 1/Qp = 1.20, 1.20-1.10, 1.30- 

 1.23. 



In a companion paper, variations of the manometric method, employing one, two or 

 three vessels, were described by Burk, Schade, Hunter and Warburg (1951). A new 

 method was suggested for manometric determination of ACO2 in which AO2 was elimi- 

 nated by an oxybiscobaltodihistidine buffer. The newly discovered "Pardee buffer" 

 (diethanolamine), able to maintain a constant CO2 pressure over nonalkahne solutions, 

 also was used. None of these new buffers proved itself satisfactory enough to become 

 a standard tool in the study of photosynthesis. 



In experiments with all these devices, quantum requirement of about 4.0 (±0.5) 

 were obtained, for "bright" periods of up to 30 min. and "dim" periods of up to 2 hours. 



In some experiments, the respirator}^ quotient in "dim" light, Qr{= — ACO2/AO2) 

 was as high as 1.26; yet, the extra gas exchange in fight had a ratio close to 1.0, indicat- 

 ing, according to Burk et al., that the "light effect" consisted not in partial reversal of 

 respiration (as suggested by Franck), but in the superposition, upon unchanged respira- 

 tion, of a photochemical process with Qp = 1.0. This was seen as further confirmation 

 of the conclusion of Warburg et al. (chapter 29, p. 901 and this chapter, section 3) that 

 respiration is not affected by light. 



The quantum requirement rose to 5.5 when optically thin suspensions (20% ab- 

 sorption of incident light, measured in the vessel of fig. 37D.24), were exposed to five 

 times the compensating light intensity. 



Warburg and Geleick (1951) made experiments that lasted 7-9 hours, 

 during which respiration was compensated by "background" light, and 

 alternating, measured green hght (alternation frequency, 1/min. or 2/min.) 



