558 PHOTOCHEMISTRY OF PIGMENTS IN VIVO CHAP. 19 



addition, however, both the carotenoids and the phycobiHns appear 

 to contribute to the sensitization of photosynthesis. Proofs of this 

 assertion are based on the analysis of the relation between wave length, 

 light absorption, and yield of photosynthesis, which will be discussed in 

 volume II, chapters 22 and 30. 



The fact that in no case have carotenoids or phycobilins been found 

 able to produce photosynthesis without chlorophyll supports the view — 

 first expressed by Engelmann as long as 60 years ago (1884, 1887) — that 

 accessory pigments do not participate directly in the oxidation-reduction 

 process, but transfer their excitation energy to chlorophyll. As stated 

 on page 515, this "physical" mechanism appears much more plausible 

 in the case of energy transfer between two dyes with overlapping ab- 

 sorption bands than in the case of a transfer from a pigment to a colorless 

 substrate. The carotenoid-sensitized fluorescence of chlorophyll in green 

 algae and diatoms (c/. Vol. II, Chapter 24) provides a direct demonstra- 

 tion of the occurrence of the process: 

 (19.17) D* + Chi > Chi* + D 



(D = carotenoid dye). As suggested previously, the extension of these 

 experiments to phycobilin-carrying red and blue algae would be of 

 considerable interest because, in these organisms, the red or blue pigments 

 must provide the largest part of the energy used for photosynthesis. 

 Furthermore, the structural similarity between phycobilins and chloro- 

 phylls makes a chemical substitution of the former for the latter as the 

 photocatalysts in photosynthesis more plausible than a similar replace- 

 ment of chlorophyll by the carotenoids. 



Bibliography to Chapter 19 



Photochemistry of Pigments in vivo 



A. Photautoxidations in vivo 



1881 Pringsheim, N., Untersuchungenuber die Lichtwirkungund Chlorophyll- 



function in der Pflanze. Engelmann, Leipzig, 1881. 



1882 Pringsheim, N., Jahrb. iviss. Botan., 13, 377. 



1883 Reinke, J., Botan. Z., 41, 697, 713, 732. 

 1885 Reinke, J., ihid., 43, 65, 81, 27, 113, 129. 



1896 Ewart, A. J., /. Linnean Soc, 31, 217. 



1897 Ewart, A. J., Ann. Botany, 11, 439. 



1898 Ewart, A. J., ibid., 12, 363. 



1903 Pantanelli, E., Jahrb. wiss. Botan., 39, 167. 



Weis, F., Compt. rend., 137. 801. 

 1905 Lubimenko, V. N., Rev. gen. botan., 17, 381. 



1907 Lubimenko, V. N., Compt. rend., 145, 1347. 



1908 Lubimenko, V. N., Ann. sci. nat. Geneve, IX, 7, 321. 

 Lubimenko, V. N., Rev. gen. botan., 20, 162, 253, 285. 



1911 Blackman, F. F,, and Smith, A. M., Proc. Roy. Soc. London B, 83, 389. 



