1870 



SPECTROSCOPY AND FLUORESCENCE OF PIGMENTS CHAP. 37C 



Porphyridium, by X 530 rrifj. (fig. 37C.41 had been constructed from a large 

 number of curves of this type). To permit the analysis, the fluorescence 

 spectra of chlorophyll and of the phycobihns in vivo had to be constructed. 

 This was done by shifting and broadening the fluorescence bands of chloro- 

 phyll a and phycoerythrin in vitro so as to fit the fluorescence spectrum 



CO 

 CO 



o 



LiJ 



CC 



o 



Q- 



o 



CO 

 03 

 < 



EFFECTIVENESS FOR 

 EXCITATION OF 

 CHLOROPHYLL FLUORESCENCE 



400 450 500 550 600 



WAVE LENGTH IN MJU 



650 



700 



750 



Fig. 37C.44. Action spectrum of excitation of chlorophyll fluorescence in 

 Porphyridium (circles), compared to the absorption spectra of the three pig- 

 ments (after French and Young 1952). 



in vivo in regions where the latter can be attributed to one of these two pig- 

 ments only ; the fluorescence spectrum of phycocyanin was then calculated 

 by subtraction. 



Points in fig. 37C.44 trace the action spectrum of the excitation of cell 

 fluorescence. Comparison with the absorption spectra indicates that, in 

 the region of 450 to 550 m/x, the main absorber is phycoerythrin ; the fluores- 

 cence of phycocyanin and chlorophyll (which, according to fig. 37C.41, 

 are co-excited throughout this region, in a constant relation to that of 

 phycoerythrin) must arise by excitation energy transfer from phycoery- 

 thrin. 



One important observation of French and Young was that changes in 

 fluorescence intensity during the induction period of photosynthesis (cf. 

 section 4 in chapter 24, and chapter 33), are confined, in red algae, to 



