136 



ANAEROBICALLY ADAPTED ALGAE 



CHAP. 6 



2(X+HZ) 



I 



[(7.10a) 



^ Light I 

 2HX 2Z 



I ^ 



E„0 



(6.1) 



H,F 



(6.5), f 



>• Eu + H,0 +F 



Va (6.2) 



(6.10) 



•-' + 

 I 

 I 

 I 



/ 



(6.7 b) 





9) 



Scheme 6.1. — Reactions in anaerobically adapted algae. (Figures in parentheses 

 refer to equations in text.) 



Normal photosynthesis. 



Adaptation and photoreduction (reaction 6.6c competes with 6.7a, thus con- 

 verting photosynthesis into photoreduction). 

 De-adaptation by the intermediates {O2! (in light) or j02i' (in excess oxygen). 



3. The Dark Reactions of Adapted Algae 



We now begin with a more detailed description of the metabolic 

 processes in adapted algae, which were enumerated on page 129. 



(I) and (II): Hydrogen Absorption and Hydrogen Fermentation. — 

 The absorption and evolution of hydrogen in darkness and in light by 

 pure cultures of Scenedesmus Di, D3 and Scenedesmus ohliquus have 

 been studied by Gaffron and Rubin (1942). During the first hour or 

 two of anaerobic incubation, the algae fermented, liberating carbon 

 dioxide and accumulating nonvolatile acids. After this initial period, 

 Scenedesmus or Raphidium cells, while continuing the steady evolution 

 of carbon dioxide, began to pick up hydrogen, if the incubation took 

 place in a hydrogen atmosphere, and to liberate hydrogen if they were 

 placed in an atmosphere of nitrogen (Fig. 9). Algae which have been 

 allowed to photosynthesize vigorously before incubation, evolved the 

 largest quantity of hydrogen, while those which have been made to re- 

 spire in the dark for a considerable length of time, gave little hydrogen. 

 The rate of absorption of hydrogen was very slow, but the total amount 

 absorbed in several days was considerable — 1 ml. of cells took up as 

 much as 2 ml. of hydrogen (simultanelusly with the evolution of 1.3 ml. 

 of carbon dioxide) . This corresponds to an exchange of about one-tenth 



