Chapter 4 



PHOTOSYNTHESIS AND RELATED PROCESSES 

 OUTSIDE THE LIVING CELL 



Complete photosynthesis — that is, reduction of carbon dioxide to 

 carbohydrates, and oxidation of water to oxygen, at low temperature 

 and with no energy supply except visible light — has never been achieved 

 outside the living cell. What has been accomplished were at best "par- 

 tial" successes, reactions which in some future time may (or may not) 

 be integrated into a complete reconstruction of photosynthesis in vitro. 



In attempting to divest photosynthesis of its association with the 

 living state, one may begin with the living cell, tear it down, and observe 

 the effects of this procedure on the different aspects of photosynthesis; 

 or one may build up from simple light-sensitive oxidation-reduction 

 systems to more complicated ones, with an eye on the maximum con- 

 version of light into chemical energy. 



Some investigators have been too impatient to use either of these 

 gradual approaches, and have spent unprofitable years in attempts to 

 reproduce photosynthesis in toto by experiments which deserve to be 

 called alchemistic rather than chemical. 



A. Photosynthesis by Dried Leaves, Isolated Chloro- 



PLASTS AND CHLOROPHYLL PREPARATIONS * 



1. Leaf Powders and Isolated Chloroplasts 



In 1881, Engelmann stated that "as soon as the structure of the 

 chlorophyll-bearing bodies is destroyed, the capacity for oxygen pro- 

 duction ceases at once and forever." Since then, the association of 

 photosynthesis with the living state of the cells has been one of the 

 fundamental facts of plant physiology. It was observed again and 

 again, that freezing, drying, boiling or poisoning puts an immediate end 

 to photosynthesis. Many tissues can live and function outside the body; 

 a hear-t will beat for days in a physiological salt solution, but the chloro- 

 plasts cease functioning the moment the cell is destroyed or damaged. 



In 1901, Friedel reported that powdered leaves, dried at 100° C. and mixed with 

 glycerol extracts from fresh leaves, produce oxygen and consume carbon dioxide in 



* Bibliography, page 94. 



61 



