PHOTOSYNTHETIC AND RESPIRATORY FIXATION OF C*02 



1631 



ent types, including sugars, proteins and even fats. It seems that this 

 redistribution of assimilated radiocarbon begins even before carbon dioxide 

 has been reduced to the carbohydrate level, by side reactions of intermediate 

 reduction products (such as amination of C3 or C4 acids) , or their involve- 

 ment in respiratory reactions. 



Aronoff, Benson, Hassid and Calvin (1947) investigated the active constituents of 

 barley seedlings exposed to light for one hour in C(14)-tagged carbon dioxide. 

 Radiocarbon was found in all fractions, with the largest accumulation in sugars (Table 

 36.1). 



Table 36.1 



Tracer Distribution in Barley Seedlings after One Hour of Photosynthesis 

 IN Tagged Carbon Dioxide (after Aronoff, Benson, et al., 1947) 



Per cent of total C * 



Plants Plants 



with without 



Fraction roots roots 



Ether-extractable acids (fatty acids) 12 . 5 2.9 



Lipids (including pigments) 6.1" 3.6* 



Amino acids 7.2 5.6 



Acids 11.3 7.7 



Sugars 25.8 35.0 



Soluble proteins 0.7 6.9 



Other water-soluble components 3.5 — 



Cellulose 2.8 3.6 



Lignin, etc 8.3 9.4 



Unaccounted 18.8 20.3 



" 0.9% in carotenoids. " 0.8% in chlorins, 0.9% in phytol. 



Aronoff, Barker and Calvin (1947) subjected the sugar fraction in table 36.1 to 

 fermentation (by yeast, or by Lactobacillus casei), and from the activity of the various 

 products determined the relative amount of C* m the different positions in the C chain. 

 The results are summarized in table 36.11; they indicate that even after a full hour of 

 photosynthesis, the tagging of hexoses was still far from uniform, and C* was preferen- 

 tially found in positions 3 and 4. 



Table 36.11 



Tracer Distribution in Sugars Photosynthesized in One Hour by Barley 

 Seedlings (Aronoff, Barker and Calvin, 1947) 



Material 



Product 



Fermented 

 by 



C* in positions 



1,6 



2,5 



3,4 



Plants with roots 



Plants without roots. . 



Hydrolyzed sugar Yeast 



Crystalline glucose L. casei 



Nonhydrolyzed sugar " " 



Crystalline glucose " " 



