ABSORPTION BY CAROTENOIDS IN BROWN ALGAE 



727 



A still more detailed analysis of the spectrum of a diatom, Navicula 

 minima, was undertaken by Tanada (1951). By extracting the pigments 

 stepwise with aqueous methanol of different concentrations, he obtained 

 evidence of the following "red shifts" in the blue- violet region (compared 

 to methanolic solution) : chlorophyll a, 8 m^t, chlorophjdl c, 20 m^t; fucox- 

 anthol, 40 m/x; other caroteaoids, 20 m/x. A comparison of the cell spec- 

 trum with the sum of so adjusted pigment spectra can be found in fig. 

 30.9B. 



How wary one must be in drawing conclusions based on a uniform shift of the bands 

 of several pigments is illustrated by figure 22.47, taken from Strain (1938): It shows the 

 absorption curves of barley leaf extracts in ethanol and in ether, and the corresponding 

 curves for the separated yellow and green pigments, in the same solvent. In ether, up 

 to 90% of the total absorption in the region 470-500 m^ is due to the yellow pigments, 

 and less than 10% is absorbed by chlorophyll; in alcohol, on the other hand, the green 



o 



400 440 480 520 560 600 640 680 400 440 480 520 560 600 640 680 

 WAVE LENGTH, m^i WAVE LENGTH, m,i 



Fig. 22.47. Effect of solvent on absorption spectra of barley leaf pigments (after 

 Strain 1938). a referred to 1 g. fresh leaves in 1 1. solution. I, all ether-soluble pig- 

 ments; II, chlorophyll a and b; III, carotenoids. 



pigments account for about one half of the total absorption in the same region. The 

 difference is due to the fact that the transition from ether to ethanol causes a stronger 

 shift of the bands of the more polar pigment — chlorophyll — than of those of the less 

 polar carotenoids (11 and 5 m^i versus 1 and 4 m/x, respectively). 



