ACTION RPECTRTTM OF GREEN TTiANTS 



1140 



curve in the green, blue and violet covers the regions where carotene, luteol 

 nnd other carotenoids con1ril)ute markedl}^ to the Hght al)sorption by 

 ChJorella. An attempt at a quantitative interpretation of the 7 curve meets 

 with some difficulties. Figure 22.44 shows that, if the absorption by the 

 carotenoids is calculated on the basis of extract spectra (by shifting all 

 bands to make their maxima coincide with the absorption peaks of live 

 cells), significant participation of carotenoids in light absorption cannot be 



GIG 



009 



008 



Q 



0.07 



z 

 < 



a 



G.06 



G.G5 



004 



400 440 480 520 560 600 



WAVE LENGTH, m/i 



640 



680 



720 



Fig. 30.1. Quantum 3-iold of photo.syii thesis as a function of wave length for 

 Chlorella (after Emerson and Lewis 1943). Points ol)tained on 19 runs are indi- 

 cated by distinct symbols. Band half widths used indicated by horizontal lines 

 of corresponding length. 



expected above 540 mju. Thus the decline in y, which first begins at 580 

 mn, cannot be attributed to the carotenoids, unless one assumes that, in 

 the living cell, their absorption bands are not merely shifted, but so strongly 

 broadened as to extend up to 580 m^i. The minimum in the quantum 

 yield curve, at 490 m/x, corresponds satisfactorily to the maximum of c aro- 

 tenoid absorption, according to fig. 22.44 (more exactly, to the center of 

 gravity of the two carotenoid peaks); but one notices that in this region 

 the carotenoids can be expected to account for 60 or 70% of the total al)- 

 sorption; while the depression of the y curve does not exceed 25%. It 

 thus again appears that, even though light quanta absorbed by the caro- 

 tenoids are less efficient than those absorbed by chlorophyll, they are not 

 entirely inefficient. 



