1876 



SPECTROSCOPY AND FLUORESCENCE OF PIGMENTS CHAP. 37C 



500 m/i (predominantly absorbed by carotenoids) or 620 m/x (absorbed only 

 by chlorophyll) ; the peak of the fluorescence band was at 682 m/x (or 683 

 muL in Chlorella). The fluorescence yield at 500 mn was 70% of that at 

 680 m^. The same ratio was found in the action spectrum of photosyn- 

 thesis in the same algae {Nitzschia DH2) . 



Fig. 37C.51 shows the absorption spectrum of the blue-green algae 

 Oscillatoria together with the action spectra of its photosynthesis (lower 

 curve) (measured polarimetrically by Duysens and Goedheer 1952) and 



CHLORELLA action spectrum ofjluorescence yield 



wave length of Incident light in mjj 



600 



Fig. 37C.50. Fluorescence of an opaque layer of Chlorella cells (after Duysens 

 1952). Quantum yield of chlorophyll a fluorescence same with excitation at 670 

 m/t (absorbed mainly by chlorophyll a) and at 650 m/i (much of it absorbed by 

 chlorophyll h). 



fluorescence (circles) . The two action spectra coincide, and both show that 

 the effectiveness of phycocyanin absorption is higher (in a ratio of 10:4) 

 than that of chlorophyll absorption — in confirmation of Haxo and Blinks' 

 findings on the action spectrum of photosynthesis in red and blue algae 

 (chapter 30). The efficiency of absorption by carotenoids is low (~ 15% 

 of that of phycocyanin), in agreement with Emerson and Lewis's estimates 

 (20%) for Chroococcus (Emerson and Lewis found, however, no photo- 

 synthetically inefficient chlorophyll absorption; cf. chapter 30). 



Fig. 37C.52 shows the fluorescence spectra of Oscillatoria excited by X 

 420 and 578 m^, respectively. The contributions of chlorophyll and 

 phycocyanin were calculated by shifting the fluorescence bands of the 

 extracts so that the peaks coincided with those of the living cells (684 m/x 

 for phycocyanin and 740 mn for chlorophyfl). A striking discrepancy 

 between the calculated sum of the fluorescences of the two pigments and 



