FLUORESCENCE OF PIGMENTS tU VIVO 



1877 



the actual fluorescence of the cells appears above 700 mu, indicating the 

 presence of a third, strongly fluorescent, pigment, not noticeable in ab- 

 sorption (perhaps, chlorophyll d, cf. chapter 30, section 6 and 32, section 6). 

 The results obtained by Duysens with the red algae, Porphyra lacineata 

 and Porphyridmm cruentum, were mentioned briefly in Vol. II, Part 1 

 (pp. 807, 812). Fig. 37C.53 shows the absorption spectrum of Porphyrid- 

 ium, the action spectrum of its photosynthesis (after Duysens and Goed- 

 heer, 1952), and points on the action spectrum curve of chlorophyll a 



OA 



0.3 



0.2 



0.1 



O 



OSC/LLATORIA 



action spectrum cfcliloPophyllfluorescence.Oand a 



absoppiion 

 spectpum 



100 



600 500 



wave length of incident light in w/z 



400 



Fig. 37C.51. Absorption and action spectra of Oscillatoria (after Duysens 1952). 

 At 680, 630, 578, 546 and 420 m/x, the contributions of chlorophyll a (chl.), phycocj^anin 

 (pcy.), and carotenoids (car.) to total absorption (upper curve) are indicated. Lower 

 curve: action spectrum of photosynthesis; points (O) indicate action spectrum of 

 chlorophyll fluorescence in an algal layer with negligible absorption. Points at X 578 

 and 420 m^t, designated □, were determined in a different way, and with various cul- 

 tures. (At 578 m/i both points were made to coincide with the action spectrum of photo- 

 synthesis.) 



fluorescence (calculated by analysis of total fluorescence spectrum, which 

 contains contributions of chlorophyll, phycoerythrin and phycocyanin). 

 The distribution of absorption between the pigments, as shown on vertical 

 scales at several wave lengths, was obtained by shifting the peaks of ex- 

 tracted pigments to their positions in vivo, and flattening the absorption 

 bands (using factors derived from the postulated inhomogeneity of pig- 

 ment distribution, as suggested in section 4). 



The curves show that photosynthesis is proportional to chlorophyll a 

 fluorescence, indicating that fluorescent chlorophyll a is the immediate 

 sensitizer, but that fluorescence of chlorophyll a is excited more effectively 

 (in fact, about 2.5 times more effectively), by light absorbed by the phyco- 

 bilins than by light absorbed by chlorophyll a itself! (Note, for example, 



