436 PLANT PHOTOPERIODISM 



linear polyenes — an unusual carotenoid — or open-chain tetrapyrroles 

 such as the phycocyanins. C-Phycocyanin as isolated from the blue- 

 green algae Aphariizomen fios-aquae, by Svedberg and Katsurai 

 (1929) has an absorption maximum at 6150 with cmax 2.76 X 10\ 

 Allo-phycocyanin has an absorption maximum at 6500 A (Haxo et al., 

 1955). The chemistry of these compounds has been very little studied, 

 but they are thought to have biladiene prosthetic groups (Lemberg and 

 Legge, 1949) with conjugation interrupted between rings 3 and 4. 

 Oxidation to biliverdin would increase the conjugation by three double 

 bonds, which could shift the absorption maxima by about 600 A as 

 observed from the separation of the red and far-red absorption maxima 

 for the photomorphogenic pigment. 



COOH COOH 



I I 



CHz CHj CHj CH2 



II I I II 



CH CH, H3C CH, CHj CHj CH CH, 



R 



Biliverdin 

 Fig. 7. Structural formula for biliverdin with indicated conjugation. 



Physical methods of finding the pigment in vivo, in contradiction to 

 physiological methods, might be based on a possible fluorescence at 

 wavelengths greater than 7000 A, appearance of free radicals as might 

 be examined by nuclear magnetic resonance, and on differential ab- 

 sorption at 6500 and 7300 A. Each would make use of the change 

 accompanying the reaction being driven from one to the other pigment 

 form. We have looked for fluorescence in this way from albino barley 

 tissue and seed. None was observed that was as intense as 1 X 10^^ of 

 that given by chlorophyll in green leaves. We are working on the 

 differential absorption at 6500 and 7300 A and on the absolute 

 absorption at 6500 A. 



Even to specify the tissue in which the pigment is functional has not 

 been possible. Nor are there sound reasons for associating the pigment 

 with cellular fractions such as protoplasmic protein, mitochondria, or 

 nuclei. The most localized reactions that have been demonstrated are 

 in coloration of the tomato cuticle (Piringer and Heinze, 1954), 



