CAROTENOIDS 



Eulgena species^ ®^ is almost identical with the most recently deter- 

 mined absorption spectrum of astaxanthin in petroleum ether, i » 4, 1 9 9 

 Mast^^^ also found that the action spectra of Phacus triqueter, 

 Trachelomonas euchlora, and Gonium species were very similar to those 

 of Euglena species. In the case of Chaltnydomonas the action spectrum 

 maximum was shifted from 474 m(jL. to 504 mfji., and in Pandorina, 

 Eudorinay and Spondylomorum, was shifted even further to about 534 

 mfx. Chemical investigations of the latter species have not been 

 reported, but if astaxanthin is present its possible occurrence as a 

 protein complex similar to that which has been reported in lobster 

 eggs and shell (see p. 170), could to quote Wald, ^* " easily meet the 

 most extreme requirements of prostistan action spectra." It must, 

 however, be emphasised that action spectra and absorption spectra 

 are not directly comparable. 2 0, 2 1 "Yhe former are represented on the 

 basis of an equal energy spectrum and the latter on the basis of an 

 equal quantum intensity spectrum. Recalculation of action spectra in 

 terms of equal quanta will result in a shift of Xmax. to shorter wave- 

 lengths (about 10 m(jL.). 2 ° ^ Carotenoid-protein complexes need not, 

 therefore, be invoked to account for action spectra with X^ax. only 

 slightly higher than X^ax. of the free carotenoid, but postulation of 

 such complexes are necessary to explain action spectra in cases where 

 the wave-length displacement is large. Galston's'* recent criticisms 

 concerning the accuracy of measurement of action spectra in higher 

 plants (see p. 88) must also be borne in mind in this connection. 



Luntz^^' has obtained maximal sensitivity (minimal threshold for 

 phototactic orientation) at 492 m(ji. for Eudorina elegans and Volvox 

 minor. Using a different technique involving the measurement of 

 times required at various wave-lengths of an equal energy spectrum, in 

 contrast to measuring directly the energy required, to elicit a standard 

 response, Laurens and Hooker ^^^ obtained maximal responses at 

 about 494 m[x. for Volvox globator. 



Manten ^ ^ ' has shown that the photic orientation in the trichomes of 

 Tolypothrix distorta v. symplocoides, which is phototropic in nature, 

 is in all probability mediated through (3-carotene. 



An observation which may prove of extreme importance is that the 

 slow but marked chromatic adaptation to its surroundings by Chlorella 

 is due to changes in its carotenoid composition. ^ ° ^ 



Function in Redox Systems 



Retrovsky ^ ^ ^ suggests that fucoxanthin, together with violaxanthin 

 and zeaxanthin, plays a part in the redox systems in algae. This is 



146 



