LUMINESCENCE OF PHOTOSYNTHETIC ORGANISMS 



121 



sity. The ability of chloroplasts to luminesce disappears during pro- 

 longed storage of chloroplasts at — 20°C., as does the Hill reaction. 

 However, lyophilized powders retain activity apparently indefinitely. 

 3. With the exception of a gradual increase in the level of lumi- 

 nescence under certain conditions during the first few minutes of 

 illumination chloroplasts do not exhibit any induction effects (6). 

 By contrast, the luminescence of intact plants evidences striking 

 fluctuations in intensity during the first few minutes of illumination 

 (1,9). These induction effects are very similar in their time course to a 

 number of other transients in photosynthesis, e.g., fluorescence 

 (10,11), ATP concentration (12,13), Oo hberation (14), and CO2 

 fixation (see Fig. 2). 



525^ Density 

 CO2 Fixotion 



Luminescence (Flow System Ca O.Ssec ofteri 

 [ATP] 



Florescence 

 Luminescence 

 (.0033 seconds after i lluminotion) 



12 3 4 



Time (Minutes) 



Fig. 2. A comparison of induction curves for various processes connected with 

 photosynthesis. Note that the time required for steady state to be reached is 

 between 90 and 120 seconds for all these processes. The ATP curve represents 

 concentration, not rate of turnover. The CO2 curve, on the other hand, is cal- 

 culated from the slope of the total fixed C^Oj as a function of time of illumination 

 (Strehler, unpublished experiments). 



These facts strongly suggest the following conclusions: 



1. The luminescence of green plants is due to an enzymatically 

 catalyzed recombination of early photoproducts in photosynthesis, 

 probably the primary reducing and oxidizing agent or the very next 

 reactants in the sequence of O2 liberation and CO2 reduction. 



2. Conditions which would be expected to cause an accumulation 

 of these photoproducts increase the luminescence and, converselj^, 



