STUDIES ON INDOLEACETIC ACID OXIDASE 



INHIBITOR AND ITS RELATION TO 



PHOTOMORPHOGENESIS 



ARTHUR W. GALSTON 



Department of Botany, Josiah Willard Gibbs Research Laboratory, 

 Yale University, New Haven, Connecticut 



The experimenter attempting to understand the biochemistry of the 

 reversible photoreaction controlling many aspects of plant growth and 

 development has available essentially three possible avenues of ap- 

 proach: 



1 . He may attempt to isolate or otherwise obtain exact information 

 about the photoreceptor pigment which represents the starting point 

 of the chain of reactions culminating in some biological response. 

 Presumably, exact knowledge of the photoreceptor could lead to addi- 

 tional information about the subsequent reactants in the chain. 



2. Going to the other end of the reaction chain, he can choose some 

 measurable biological effect of the irradiation, such as seed germina- 

 tion, bean hook opening, or floral initiation, and study such subjects 

 as the kinetics of the forward and back reactions, the relation of these 

 reactions to various growth-regulating substances, and effects of other 

 environmental variables on the course of the reaction. Presumably, this 

 type of study, being pursued by so many people, will give some indi- 

 cation of the kind of growth regulatory system through which the 

 initial photoreaction exerts its ultimate effects. 



3. Finally, if he knows of some precise chemical change produced 

 directly by the reversible photoreaction, he can try to understand the 

 mechanism by which this change has resulted from the irradiation 



^ These investigations have been supported for several years by a series of 

 grants from the National Science Foundation. Certain of the experiments were 

 performed with the technical assistance of Suzanne L. Fried and Hava War- 

 burg. The work on the inhibitor and cofactor for indoleacetic acid oxidase has 

 been performed by Dr. Z. Rose and Dr. H. Sharpensteen, respectively, under 

 partial support furnished by the American Cancer Society. 



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