FLUORESCENCE IN TWO-PIGMENT SYSTEMS 

 J. L. Rosenberg and Tevfik Bigat 



We report here on some of our recent experimental observations 

 of fluorescence in algae and leaves, with particiilar reference 

 to the interactions between the two pigment systems and between 

 the two photochemical reactions of photosynthesis. A ixnified 

 model for energy collection and for the photochemical sequence 

 of photosynthesis will be assiomed, applicable to green algae, 

 phycobilin- containing algae, and green leaves. 



RED ALGAE 



Experimental 



Fluorescence observations of Porphyridium cruentum were 

 carried out under conditions of chromatic transients occiirring 

 when the wave-length of illumination is changed. In addition 

 steady-state intensities of fluorescence were observed under 

 differential excitation of the chlorophyll a and of the 

 phycobilins. Days ens ' publication of a similar study appeared 

 while our own manuscript was in preparatlon(l ) . We therefore 

 need not give great experimental detail, but mention partic- 

 ularly those points of difference between oixr work and his. 

 We will use his notation wherever possible: 



The density of the cell suspension was such as to allow 25- 

 50fo transmission at 680 m\i in the 1 mm optical path of the 

 fluorescence cell. The sample could be illuminated with two 

 beams entering the cell along the same path, a blue beam at 

 k-k^ m|j, absorbed principally by chlorophyll a and a green beam 

 peaking at 535 m^i absorbed principally by phycoerythrin. These 

 beams served both as actinic and fluorescence excitation beams . 

 Fluorescence was observed at 4-5° to the actinic beam through a 

 679 mp. interference filter appropriately supplemented to 

 eliminate all scattering and phycobilin fluorescence. 



For approximately equal incident intensities of the two beams, 

 the steady-state fluorescence d-uring simultaneous irradiation was 



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