SPECTRA OF PHOTOSYNTHETIC PIGMENTS 



367 



TRANSFER OF ENERGY BETWEEN PIGMENTS IN LIVE PLANTS 

 AS DETERMINED BY FLUORESCENCE SPECTROSCOPY 



The manner of the participation of various pigments in photosynthesis 

 has long been a question of interest. Since all photosynthetic organisms 

 with the exception of bacteria contain chlorophyll a, it has been proposed 

 that the other pigments might function by transferring their absorbed 

 energy to chlorophyll. One way to test for the occurrence of this energy- 

 transfer process is to see if light absorbed by the other pigments can 

 cause chlorophyll to fluoresce in the live cells. This method was used by 

 Wassink and Kersten (1944) and by Button et al. (1943) with the diatom 



Table 6-1. The Excitation of Chlorophyll Fluorescence by Light 

 Absorbed by Carotenoids in Nitzschia and in Chlorella 



Nitzschia, which is rich in yellow pigments, especially fucoxanthin, and 

 with Chlorella pyrenoidosa. They calculated the fluorescence-yield ratios 

 at wave lengths absorbed by chlorophyll alone and at some wave lengths 

 absorbed by both chlorophyll and carotenoids. The results obtained by 

 Button and Manning are given in Table 6-1. They indicate energy 

 transfer from carotenoids to chlorophyll even though some error tending 

 to increase the apparent amount of energy transfer may have been intro- 

 duced as a result of reabsorption of fluorescent light within the cells. 



An attempt was made to measure energy transfer in red algae in a 

 similar manner (Van Norman et al., 1948) to determine whether phycoe- 

 rythrin transferred energy to chlorophyll or took part directly in the 

 photosynthetic mechanism without the intermediate assistance of chloro- 

 phyll. These algae presented a more complicated situation, however, 

 since the phycoerythrin and phycocyanin also fluoresce and their fluo- 

 rescence overlaps that of chlorophyll, so that it is difficult to determine 

 how much of the red fluorescence is due to chlorophyll. 



