68 



FLUORESCENCE SPECTROPHOTOMETRY 



chlorophyll fluorescence. It also shows that other carotenoids absorb- 

 ing at shorter wavelengths than fucoxanthin are less effective in 

 transferring energy to chlorophyll. 



400 



500 600 



WAVELENGTH 



700 m>j. 



Fig. 17. The absorption spectrum of the thin suspension of Nitzschia in dilute 

 agar (small circles), as compared with the action spectrum for fluorescence 

 excitation (heavy line). The lower straight line is the estimated contribution 

 of scattering to the measured absorption; it was used as the baseline above 

 which the action spectrum was plotted. 



Phycobilins and Chlorophylls in Red Algae 



The spectra of red algae demonstrate some of the more complex 

 fluorescence phenomena. They contain the fluorescent pigments 

 phycoerythrin and phycocyanin in addition to chlorophylls a and d 

 so that fluorescence spectra of mixtures are obtained. 



Haxo and Blinks (1950) have found that the hght absorbed by 

 phycoerythrin and phycocyanin is used in photosynthesis even more 

 efficiently than that absorbed by chlorophyll. Do these accessory 

 pigments act directly in photosynthesis or do they participate by 

 transferring their energy to chlorophyll a, which seems to be a more 

 or less universal photosynthetic pigment? The fluorescence spectra 

 for various incident wavelengths of measured intensity from Porphyri- 

 diiim cruentum are given in Fig. 18. We see the typical peaks due to 

 phycoerythrin, 678 mix, phycocyanin, 655 m/x, and chloroph>'ll a, at 685 

 m/x. Figure 19 shows the analysis of a similar curve in terms of the 



