CHAPTER 7 



THE PRODUCTION OF OXYGEN BY 

 PREPARATIONS OF ISOLATED CHLOROPLASTS 



INTRODUCTION 



The assimilation of COg requires a reduction process; it 

 must be accompanied by a complimentary process of oxida- 

 tion which in the green plant results in the production of 

 molecular oxygen. This production of molecular oxygen is a 

 characteristic response of the illuminated green plant to the 

 presence of carbon dioxide. In this chapter we shall be con- 

 cerned with the mechanism of the production of oxygen 

 rather than with the mechanism of the reduction of carbon 

 dioxide. 



When the cells of the green leaf are broken it is possible 

 to separate a fluid which contains chloroplasts and chloro- 

 plast fragments but such preparations produce only minute 

 amounts of oxygen in the light. The early work of Haber- 

 landt and of Ewart in the late nineteeenth century had shown 

 that chloroplasts isolated from the leaves of a moss or 

 Selaginella produced in the light an amount of oxygen so 

 small as to be detectable only by the use of luminescent 

 bacteria. In 1925 preparations from dried leaves were shown 

 by Molisch also to produce small amounts of oxygen upon 

 illumination, but this was observed only when the leaves 

 were powdered under water and the powder left in contact 

 with the water extract. This in vitro reactign with light was 

 originally considered to represent a very feeble activity of 

 normal photosynthesis, but this interpretation was shown 

 to be unjustified by the work of Hill. Using chloroplast pre- 

 parations from Stellaria media and Lamium album. Hill and 

 Scarisbrick (1940) showed that the photochemical produc- 

 tion of oxygen required the presence, not of carbon dioxide, 

 but of a suitable hydrogen acceptor and that when this was 

 added to the preparation oxygen could be produced in light 



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