1416 INDUCTION PHENOMENA CHAP, 33 



carbon dioxide in light, described by Emerson and Lewis and illustrated 

 by figures 29.5 and 33.13. Emerson and Lewis suggested that this gush 

 (and the compensating slow uptake of carbon dioxide in the dark) is due to 

 the presence of a photolabile compound not directly related to photosynthe- 

 sis, the photochemical decomposition of which is superimposed upon the 

 latter. Blinks and Skow, in discussing the "acidity gush" in light (and 

 "alkalinity gush" in the dark), which they had observed in measurements 

 with the glass electrode (c/, fig. 33.12), listed several possible interpreta- 

 tions: (1) release of carbon dioxide by a photolabile compound; (^) light- 

 stimulated respiration; (S) production of an acid stronger than carbonic 

 acid, as a first product of photosynthesis; (4) photodecomposition of plant 

 acids (e. g., malic acid), with the liberation of carbon dioxide; and (5) 

 photochemical consumption of a base (e. g., ammonia). Hypothesis 3 is im- 

 probable for reasons discussed in chapter 20; furthermore, it does not 

 explain the reversibility of the gush. The latter also rules out hypothesis 

 4- Hypothesis 5 discounts the probable identity of the acid gush with the 

 carbon dioxide gush of Emerson and Lewis. We are thus left with hypoth- 

 eses 1 and 3 (the latter can explain a gush of gaseous carbon dioxide, if 

 it is assumed that the synthesized acid reacts with a bicarbonate reserve 

 in the cell). 



In chapter 8, we described two reversible carbon dioxide uptake mech- 

 anisms operating in green plant cells. One is due to carboxylation and 

 probably leads, among other products, to the immediate reduction sub- 

 strate of photosynthesis. (We say "among other products" because it has 

 recently become clear that reversible carboxylations also occur, in plant 

 tissues as well as in animal tissues, without direct relation to photosynthe- 

 sis, as a part of respiratory and fermentative reactions.) The second car- 

 bon dioxide uptake mechanism is based on buffer equilibria (involving al- 

 kaline earth carbonates and alkali phosphates), and is either unrelated, or 

 only indirectly related to photosynthesis. Before postulating a new re- 

 versible carbon dioxide-absorbing mechanism to account for the results of 

 Emerson and Lewis, and Blinks and Skow, one must consider the possi- 

 bility that the gush is due either to the photochemical decomposition of 

 the complex A -002, or to the decomposition of bicarbonate reserves, in 

 consequence of the photochemical formation of a comparatively strong acid. 



The first hypothesis was suggested by Franck (1942), and appears the 

 more plausible, since we have no other indications that photosynthesis 

 leads to acidification of the cell contents. Furthermore, the maximum 

 volume of the carbon-dioxide gush, as measured by Emerson and Lewis, 

 appears to correspond to the amount of the carbon dioxide acceptor com- 

 plex, A -002, in the cells (i. e., it is about equivalent to the content of 

 chlorophyll). 



