1966 KINETICS OF PHOTOSYNTHESIS CHAP. 37D 



lated that, if 85% of the respiration intermediates, of the type of PGAP, 

 formed in the period of alternating illumination, could be utilized for "anti- 

 respiration," this would be enough to account for the calculated quantum 

 requirement. 



The calculation can be made as follows: If the steady respiration is R (moles O2 

 per unit time), we assume that its compensation requires 8/E einstein in the dim period, 

 but could be achieved by 2R einstein in the bright period, if "anti-respiration" were 

 100% effective in the second case. More generally, [8(1 — x) + 2x] X R = 8R — 6Rx 

 quanta will be needed, where x is the fraction of total respiration reversed in light. This 

 switch frees 6Rx einsteins for photosynthesis. If the observed increment of photosynthe- 

 sis in unit time during the "bright" period is AP, and the number of additional photons 

 absorbed from alternating light, 7^, Warburg calculates the quantum requirement from 

 the simple equation I/7 = n = Ia/AP (= 2.9). Franck's equation for the calculation 

 of the "true" jaeld, m, is, on the other hand, I/70 = no = (/a + 2 X (iRx)/AP. 



The factor 2 in parentheses reflects the fact that the 6/?x einsteins are available dur- 

 ing both phases of alternating light — the 1 minute periods when the monochromatic beam 

 is "on," as well as the 1 minute period when this beam is "off." 



With AP = 2R, this equation gives no = 2.9 -f- Qx; for no to be equal to 8.0, a* must 

 be 0.85, i. e., 85% of total respiration must be compensated by "antirespiration" during 

 alternating illumination. 



Franck's interpretation is thus quantitatively possible, even in a case in 

 which the average net photosynthesis in the one hour "bright" period is 

 twice the steady respiration in the "dim" period. However, one needs in 

 this case the somewhat extreme assumption that respiration in the whole 

 cell (not only in the chloroplast) is, on the average, 85% inhibited (or, more 

 exactly, reversed) in alternating light. 



(3) The observations illustrated by fig. 33. 6A are interpreted by 

 Franck as demonstrations of a new kind of induction phenomena, rather 

 than as revelation of the two-stage mechanism of photosynthesis. The 

 pecularity of these induction effects is that they cause (apparent) gains 

 rather than the — more familiar— Zosses in the photosynthetic yield in the 

 first minute or two of illumination. 



This interpretation has caused us to deal with the minute hght-minute 

 dark experiments in chapters 33 ("Induction Phenomena") and 34 ("Photo- 

 synthesis in Flashing Light"). The essential point in their interpretation 

 by Franck is the attribution of the exceptionally high quantum yield in the 

 first minute of illumination to temporary shortage of the carbon dioxide 

 acceptor (called A or RH in chap. 27, specified as ribulose diphosphate in 

 chapter 36). This shortage, caused by metabolic destruction of the ac- 

 ceptor during the dark period, invites respiration intermediates (PGA, or 

 PGAP) to enter the photosynthetic cycle; as long as they are being uti- 

 lized, the quantum requirement of the photochemical process can be as low 

 as 2. If alternation is not between light and dark, but between "bright" 



