FLUORESCENCE OF PIGMENTS m VIVO 



1875 



by chlorophyll h (Fig. 37C.49). The single fluorescence peak is located at 

 683 m/x; this indicates that chlorophyll a is the fluorescent pigment and 

 suggests that practically all quanta absorbed by the b component are trans- 

 ferred to a before dissipation or re-emission. (This result is in disagree- 

 ment with the earlier— and probably less reliable — observations listed in 

 tables 24.1 and 24.11, in which chlorophyll h fluorescence band was noted 

 at 655-657 m^, in Ulva and Elodea.) 



Fig. 37C.50 shows the action spectrum of fluorescence of chlorophyll a 

 in Chlorella (to minimize re-absorption, only fluorescent light above 720 m^ 



100 



- s; 



51 



CHLORELLA 

 fluorescence spectra 



50 



800 



650 



150 100 



Fig. 37C.49. Fluorescence spectrum of Chlorella excited at X 420 and 480 m^ (the 

 latter appreciably absorbed by chlorophyll h) (after Duysens 1952). The fluorescence 

 peaks are at 683 mn, slightly beyond the main absorption peak of Chlorella at 680 m/i. 

 No fluorescence peak is noticeable shghtly beyond the absorption peak of chlorophyll 6 

 at 650 mju. (Corrected for re-absorption of fluorescence in the cells.) 



was measured; it belongs to the second fluorescence band and is not 

 significantly re-absorbed). The yield is the same at 650 m^u (where 42% of 

 total absorption is due to chlorophyll h) and in the region of exclusive 

 chlorophyll a absorption (670 m/x). Whether the drop at X < 650 m^ is 

 real, or is caused by geometrical-optical conditions, is uncertain; the sharp 

 drop at X > 680 mju undoubtedly is real {cf. table 37C.5). The yield was 

 measured also at 480 mju ; analysis of these results indicated an about 40- 

 50% effectiveness of energy transfer from carotenoids to chlorophyll a 

 {cf. chapter 24, p. 813, and chapter 35, section 2). 



Duysens also confirmed the observations of Button, Manning and 

 Duggar (p. 814) of the carotenoid-sensitized chlorophyll fluorescence in 

 brown algae. The fluorescence spectrum was the same whether excited at 



