422 RADIATION BIOLOGY 



ever, the amount of chlorophyll accumulated appeared to be less in a 

 carbon dioxide-free atmosphere than under normal conditions (ibid.). 



Other Gases. Ozone was found by Boehm (1865) to be detrimental to 

 chlorophyll accumulation. 



Carbon monoxide decreases the rate of chlorophyll formation (Yocum, 



1946). 



Sulfur dioxide and vapors of ether, fuming nitric acid, and ammonium 

 thiocyanate in concentrations insufficient to kill the leaf have little or no 

 effect on the protochlorophyll-chlorophyll transformation (Scharfnagel, 

 1931). 



6. INFLUENCE OF NUTRITION ON THE FORMATION 

 AND ACCUMULATION OF CHLOROPHYLL 



Are the constituent elements of chlorophyll derived directly from the 

 inorganic components of the nutrient medium? 



A direct photosynthetic utiUzation of carbon dioxide for chlorophyll 

 formation is not indicated because of the following facts: Chlorophyll is 

 formed in plants illuminated in air free of carbon dioxide (Rombeck, 

 1943), and chlorophyll extracted from plants that have photosynthesized 

 labeled carbon dioxide does not contain labeled carbon in excess of other 

 substances formed concurrently (Ruben et al., 1939; Clendenning, 1950). 

 Chlorophyll also is found in organisms that do not utihze carbon dioxide 

 photosynthetically (Davis, 1948). 



The hydrogen contained in chlorophyll is undoubtedly derived from 

 organic intermediates, not directly from water. No labeled hydrogen 

 (tritium) was found in the chlorophyll obtained from ChloreUa pyrenoidosa 

 cells that had photosynthesized for 3 hr in tritium oxide (Norris et al, 

 1942). Also the proportion of labeled hydrogen (deuterium) was the 

 same in the porphyrin and phytyl fractions of chlorophyll produced dur- 

 ing photosynthesis in deuterium oxide by ChloreUa cells (Calvin and 

 Aronoff, 1948). This suggests that the hydrogen in chlorophyll comes 

 from the metabolism of organic compounds rather than directly from 

 water. 



The case of nitrogen is not so clear, because the chlorophyll content of 

 organisms grown in media of different nitrogen concentrations is propor- 

 tional to the nitrogen concentration. Fleischer (1935) demonstrated that 

 cells of ChloreUa Cornell No. 11 (cf. Mandels, 1943) could be grown with 

 very small chlorophyll content when the nitrogen content of the nutrient 

 medium was very low, and that the chlorophyll content of the cells could 

 be increased by increasing the nitrogenous nutrients. When the nitrogen 

 was changed from 10 to 80 ppm, the chlorophyll content of the cells was 

 changed from 1 X 10"^ to 13 X 10"^ per 10 mm^ of packed cells. Van 

 Hille (1938) cultivated C. pyrenoidosa cells in two nutrient solutions con- 

 taining potassium nitrate in concentrations in the ratio of 4 to 1. The 



