CHLOROPHYLL SYNTHESIS 3i3 



from non-green precursors, although there is much less agreement regarding 

 the exact nature of the chemical changes involved. Lubimenko (1926, 1927, 

 1928) and others believe that the oxidation of a colorless compound leucophyll 

 results in the production of the pigment cJilorophyllogcn. This latter com- 

 pound, although green, is seldom present in plant tissues in sufficient quantities 

 to impart a color to them. Chlorophyllogen is supposed to be the immediate 

 precursor of chlorophyll. Furthermore it is considered that in the algae, 

 mosses, ferns, and conifers the change of chlorophyllogen to chlorophyll does 

 not require the intermediation of light, but in the angiosperms this transforma- 

 tion seldom occurs except in the presence of light. Under various conditions 

 such as extraction with alcohol or acetone it is further supposed that chloro- 

 phyllogen is converted into another distinctive compound called proto- 

 chlorophylh which is not believed to be directly involved in the sequence of 

 reactions leading to the production of chlorophyll. 



Eyster (1928) and Noack and Kiessling (1929, i93o) believe experi- 

 mental results warrant another interpretation of the chemistry of chlorophyll 

 synthesis. They contend that the pigment protochlorophyll is the immediate 

 precursor of chlorophyll. This compound can be extracted from the inner 

 'coats of seeds of certain cucurbits and prepared in a pure form. It ex- 

 hibits a red fluorescence similar to that of chlorophyll and possesses a promi- 

 nent absorption band between wave lengths 620 inp. and 640 lUfx. Chloro- 

 phyll is believed by these investigators to be an oxidation product of pro- 

 tochlorophyll and the photo-oxidation of protochlorophyll in green cells is 

 believed to be the final step in the formation of chlorophyll in those species 

 in which light is required in this process. Protochlorophyll changes rapidly 

 and quantitatively into chlorophyll on exposure to light. 



If a solution of chlorophyll in acetone is exposed to bright light its color 

 soon fades due to a destructive effect of light upon the chlorophyll. This is 

 undoubtedly a photo-oxidation process, since it is accompanied by the absorp- 

 tion of oxygen. 



Strong light is also supposed to bring about the disintegration of the 

 chlorophyll in leaves, although at a less rapid rate than in chlorophyll solu- 

 tions. In leaves exposed to intense light, therefore, synthesis and decomposi- 

 tion of chlorophyll are probably going on simultaneously. In accord with 

 this concept are the results of Shirley (1929) who found in a number of 

 species of plants that the chlorophyll content per unit leaf weight or per unit 

 leaf area increased with decreasing light intensity until a relatively low in- 

 tensity was reached. Further decrease in light intensity below this value 

 caused a decrease in chlorophyll content. 



3. Oxygen. — In the absence of oxygen etiolated seedlings fail to develop 



