CHLOROPHYLL FORMATION 435 



common to both chlorophylls. A specific proposal for the inclusion of 

 these concepts would be premature at the present time. 



But in addition to and beyond the biosynthetic steps in the formation 

 of chlorophyll, there are other factors that must be considered relative to 

 chlorophyll accumulation. The work on the genetic mutants of corn has 

 demonstrated that not only must sufficient precursor be formed to give 

 normal greening but that conditions must be favorable for the protection, 

 and consequent accumulation, of chlorophyll once it has been formed. 

 Albinism probably is not so much the result of a "genetic block" in the 

 chain of biosynthetic reactions leading to the formation of chlorophyll 

 as it is a disturbance of factors that protect the chlorophyll already 

 synthesized. 



There is a close connection between the biosynthesis of chlorophyll 

 and the protoplasm in which it arises. Boehm clearly recognized this 

 and articulated it in his name for chlorophyll precursor — "chlorophor." 

 The interconnection between the biological system and the biosynthesis of 

 chlorophyll has been demonstrated by the action of inhibitors on chloro- 

 phyll formation, particularly by the use of streptomycin. This inhibitor 

 acts through the hindering of chloroplast formation. When the chloro- 

 plasts cannot become organized, chlorophyll formation fails. 



If this review has any virtue, perhaps it resides in highlighting the 

 many unanswered questions remaining in fields that have already been 

 explored and in pointing out whole areas that remain unexplored. The 

 organic and physical chemistry of the extracted chlorophylls has advanced 

 far beyond the biochemistry and physiology of the holochromatic pig- 

 ments. The investigation of the vital reactions, not merely of the two 

 best-known chlorophylls but of all of them, will bring rich rewards in the 

 foreseeable future. • 



REFERENCES 



Chlorophyll formation was reviewed in "Biological Effects of Radiation," Vol. II 

 (Duggar, 1936) by Inman, Rothemund, and Kettering and by Spoehr and Smith. 

 Comprehensive reviews have been published by Liro (1909), by Lubimenko (1926- 

 1928), by Aronoff (1950), and by Granick (1951). 



For the chemistry of chlorophyll and for the relation of chlorophyll to photosyn- 

 thesis, the reader is referred especially to WillstJitter and Stoll (1913, 1918), StoU and 

 Wiedemann (1938), Fischer and Stern (1943), and Rabinowitch (1945, 1951). 



Alamercery, J., C. L. Hamner, and M. Latus (1951) Chlorophyll inhibition and 

 growth regulation by several tetronic acid derivatives. Nature, 168: 85. 



Aronoff, S. (1950) Chlorophyll. Botan. Rev., 16: 525-588. 



Artari, A. (1902) Ueber die Bildung des Chlorophylls durch griine Algen. Ber. deut. 

 botan. Ges., 20: 201-207. 



Bear, F., and R. Coleman (1949) Hunger signs in crops. A symposium. The Amer- 

 ican Society of Agronomy and The National Fertilizer Association, Washington. 



Beijerinck, M. W. (1904) Chlorella variegata, ein bunter Mikrobe. Rec. trav. botan. 

 neerl., 1: 14-27. 



