FLUORESCENCE OF PIGMENTS lU VIVO 



1871 



chlorophyll fluorescence, and do not appear in the fluorescence of the phyco- 

 bilins. In agreement with the observations Franck and Shiau made on 

 green algae, induction effects were much stronger in ''old" than in "young" 

 cultures of red algae. 



The effect of light intensity on fluorescence yield (c/. chapter 28, part B) 

 also are restricted to chlorophyll. As mentioned briefly on p. 1051, the 

 yield of fluorescence of phycobilins in Porphyridium is independent of light 



-1 — I — 1 — 1 — 1 — I — r 



— 1 1 r 



~-| 1 r"~1 r- 



LOW INCIDENT 

 INTENSITY 



yOlFFERCNCE^^, ^ 



/ BETWEEN LOW 'and hTgII' 

 INTENSITY CURVES 



600 650 700 750 



WAVE LENGTH IN MjJ 



Fig. 37C.45. Effect of light intensity on 

 fluorescence spectrum of Porphyridium 

 (after French and Young 1952). 



intensity, while that of chlorophyll (measured in the steady state, six 

 minutes after beginning of illumination) is lower in stronger light. This 

 leads to changes in the shape of the fluorescence spectrum with the intensity 

 of illuminating light, illustrated by figure 37C.45. 



All these observations agree with the hypothesis that chlorophyll is 

 the only pigment directly related to the photochemical processes in photo- 

 synthesis. 



Duysens' (1952) experiments dealt with the purple bacteria as well as 

 with algae (c/. pp. 810 and 812, respectively). Figs. 37C.46 and 47 show 

 the absorption and fluorescence spectra of the purple bacteria Rhodo- 

 spirillwn ruhrum and Chromatium, respectively. The first species seems to 

 contain only a single bacteriochlorophyll complex (it has a single infrared 

 absorption band); the second, three such complexes (three infrared 



