FLUORESCENCE OF PIGMENTS lU VIVO 



1879 



phyll a, and an unknown, fluorescent pigment (chlorophyll df). The 

 fluorescence peak at 725 m/x, ascribed to the contaminating pigment 

 (chlorophyll df), is prominent in the fluorescence spectrum of Porphyra 

 (fig. 24.5) ; its presence is less certain in Porphyridium. 



0.6 



ou 



0.2 



PORPHYRIDIUM CRUENTUM 



^ 7 points of action ■spectrum of 



cMorophyll fluorescence : v. (F. Y); A ; 



action specirum of ..__ 

 / photosynthesis ' 



WO 



600 



A/ in mjjL 



Fig. 37C.53. Absorption and action spectra of photosynthesis and chlorophyll 

 fluorescence in red algae (after Duysens 1952). Contributions of the several pigments 

 to total absorption are shown by line segments (chl. = chlorophyll, pcy. = phycocyanin, 

 per. = phycoerythrin, car. = carotenoids). Action spectrum of chlorophyll fluores- 

 cence based on analysis of the fluorescence spectrum. Points marked V, after French 

 and Young; points marked A, ▼, A, measurements with different cultures; the three 

 points marked ▲ at 420 m^u, also obtained with different cultures. Photosynthesis 

 roughly proportional to chlorophjdl fluorescence. Comparison of action spectrum of 

 fluorescence with absorption spectrum, at X 680, 630 and 560 m/t, shows that Ught ab- 

 sorbed by phycobilins strongly excites chlorophyll fluorescence. 



(c) Re-ah sorption of Fluorescence 



In discussing their measurements, French and Young noted the efl"ects 

 of re-absorption of fluorescent light in the cells (concerning the same effect 

 in solutions, see p. 746). This effect is most pronounced in the case of 

 chlorophyll, where the fluorescence band overlaps strongly the absorption 

 band; in dense green tissues, the first fluorescence peak can be shifted, 



V_ 



