NEW PLASHING LIGHT EXPERIMENTS 



1467 



6. Flashing Light Experiments Calling for Revision or 

 Supplementation of the Emerson-Arnold-Franck Mechanism 



The above-described results of the flashing light experiments of War- 

 burg, Emerson and Arnold, Kohn, Franck and Weller, Rieke and Gaffron, 

 Clendenning and Ehrmantraut, and Ehrmantraut and Rabinowitch seemed 

 to add up to a consistent picture, and to provide one of the few firm factual 

 bases for the kinetic analysis of photosynthesis. It seemed to be well es- 

 tablished that the normal maximum rate of photosynthesis in strong steady 



25° P'"'"' = 7.3 X 10' 

 — O 



15° P""" = 5.3 X 10" 



1° P'"""- = 3.7 X 10" 



0.3 



0.4 



Vi 



sec. 



Fig. 34.21. Yield of flashes of saturating energy in Chlorella ellipsoidea as function of 

 dark interval (after Tamiya and Chiba 1949). The yields are expressed in moles O2 

 per gram dry weight per flash; to express them in moles O2 per mole chlorophyll, multi- 

 ply the ordinates by about 2 X 10*. 



light (Pmax! equal to about one molecule oxygen per molecule of chlorophyll 

 every 20-30 seconds), can be factorized into a concentration factor of the 

 order of Chlo/2000 (or Chlon/2000, with n a small number, perhaps 4 or 8) 

 and a monomolecular rate constant of the order of 100 sec.~^ at 20° C. 

 These two separate constants accounted for flash saturation as function of 

 flash energy, and for flash saturation as function of the duration of dark 

 intervals, respectively. A remaining difficulty was the enhancing effect 

 on the (apparent, or true) light energy utilization (1^1 > 1) of dark inter- 

 vals of the order of 1 second, or longer. Tentatively, this favorable effect 

 of relatively low frequencies of alternation could be related to CO2 supply 

 limitations, or to the "bursts" and "gulps" described in chapter 33 (which 

 affect most strongly the gas exchange in the first seconds of exposure) . 



