1172 



TITE Lir.TTT FACTOR. III. fOT.OTl 



CTI.\P. 30 



acth'ity of the carotenoids. This hypothesis was supported by the action 

 spectrum of the brown alga Coilodesme, determined polarographically by 

 Haxo and BHnks (1950) and reproduced, together with the absorption 

 spectrum, in figure 30.1 IB. 



Dutton and Manning also performed experiments in stronger light, in which they 

 first measured photosynthesis in saturating red light, and then added violet light. They 

 found — as one would expect — no appreciable effect of this additional illumination on 

 the yield, -.mA interpreted this as a proof that photosynthesis in blue light, although 

 sensitized by both chloroph3ll atul the carotenoids, is limited by the same dark reaction 

 as photosynthesis in red light, which is sensitized by chlorophjdl alone. 



Wassink and Kersten (1946) studied the diatom Nitzschia dissipata; 

 the spectroscopic results of this study were presented in Chapter 22 (p. 706). 

 These investigators made measiu'ements of the rate of photosynthesis in 



012 



0.10 



0.08 



0.06 



0.04 



0.02 



400 440 480 520 560 600 640 680 720 

 WAVE LENGTH, rn/i 



Fig. 30.9A. Quantum yield (ordinate) of photosynthesis as a 

 function of wave length for A^. minima (after Tanada 1951). 



light of different color, isolated bj^ filter combinations. They reduced the 

 data to a common average intensity (7.3 kerg/cm.^ sec.) in the assumption 

 that they worked in the linear part of the light curve. (This assumption 

 was based on the type of light curves, showing a verj'- extensive linear part, 

 which had been obtained by the Dutch group for green plants, diatoms and 

 purple bacteria, cf. fig. 28.14B and table 28.11; this shape was not con- 

 firmed b}^ other investigators.) Wassink and Kersten estimated that 

 the yield per absorbed quantum is the same in Nitzschia and in ChloreUa, 

 and is constant in red, yellow, and yellow-green light; in blue-green light, 

 it is somewhat lower in both organisms. They concluded that in contrast 

 to other carotenoids, fucoxanthol is fully effective as sensitizer of photo- 



