FLUORESCENCE INDUCTION PHENOMENA 1375 



cumulated reducing intermediates is achieved by a simple photochemical 

 reaction, it should require less time in strong than in weak light. 



This hypothesis links the induction period of hydrogen assimilation 

 with the "hydrogen burst" produced by the same algae in carbon dioxide- 

 free nitrogen atmosphere. In both cases, the first effect of light is oxida- 

 tion (dehydrogenation) of the accumulated fermentation products, the 

 hydrogen being either utilized for the reduction of carbon dioxide, or re- 

 leased into the atmosphere. 



The assumption of "photosynthesis at the cost of fermentation prod- 

 ucts" was also used by Franck, Pringsheim and Lad (1945) in the explana- 

 tion of the cyanide-insensitive burst of oxygen production in the first 

 minutes of illumination of anaerobically incubated algae. These authors 

 have also contributed essentially to the understanding of the time curves 

 of gas exchange in Gaffron's hydrogen-adapted algae, by showing that the 

 return to normal photosynthesis can be postponed indefinitely by prevent- 

 ing the oxygen evolved by residual photosynthesis from accumulating in 

 the closed system. 



9. Induction in Hill Reaction 



Clendenning and Ehrmantraut (1950) noted that no induction occurs 

 in the liberation of oxygen by ChloreUa cells with quinone as oxidant; the 

 same cells showed the usual induction period of about 5 minutes in bicar- 

 bonate solution. No induction losses were found in the oxygen liberation 

 by isolated chloroplasts with quinone or ferrocyanide as oxidants. The 

 theoretical significance of these results will be discussed later. 



No induction was observed in the Hill reaction of chloroplasts by Hill 

 and Whittingham (1953) with the hemoglobin method of spectroscopic 

 oxygen determination. 



B. Fluorescence and Absorption Changes during the 



Induction Period* 



1. Fluorescence Induction Phenomena in Leaves, Algae, Chloroplasts 



and Chlorophyll Solutions 



It was said before that fluorescence is one of the few if not the only 

 property of chlorophyll that can easily be measured simultaneously with 

 photosynthesis. All determinations of gas exchange, even by electrical 

 or optical methods, are sluggish, since the gas has to be moved from the in- 

 terior of the plant cell to the locus of measurement (or vice versa). Fluores- 

 cence, on the other hand, is measured practically instantaneously; this 



* Bibliography, page 1431. 



