SOME METABOLIC CONSEQUENCES OF 

 THE ADMINISTRATION OF INDOLEACETIC ACID 



TO PLANT CELLS 



A. W. GalstonI 



Kerckhoff Biological Laboratories, California Institute of Technology, 



Pasadena, California^ 



Our knowledge of the mode of action of auxin in promoting the extension 

 growth of plant cells is at present so primitive and fragmentary that almost 

 any biochemical fact which can be related to auxin is of interest. No man 

 can predict which of the numerous leads now being explored will result in a 

 final elucidation of this problem. This permits us, with a clear conscience, 

 to devote ourselves to pursuits which, at least at present, do not seem to be 

 aimed at the heart of the problem, but which are none the less of considerable 

 interest. 



It is now well known that 3-indoleacetic acid (lAA) is a naturally 

 occurring auxin of wide occurrence in the plant world, and of great quantita- 

 tive significance in the auxin economy of the plant (Larsen, 1951). Indeed, 

 in many instances, it appears that all of the auxin in the plant is either lAA 

 or closely-related compounds, such as indoleacetonitrile or indoleacetalde- 

 hyde, which can be metabolized to lAA. For this reason it seems to be of 

 interest, in investigating the mode of action of auxin, to analyse in detail the 

 metabolic consequences of the administration of lAA to tissues which can 

 respond to this compound. 



In such a biochemical analysis, we may note at least two separate categories 

 of events : 



(1) The lAA itself undergoes certain alterations: 



[a) A small portion is firmly bound to protein, apparently via peptide 

 and other linkages, as lAA. 



[b) A much larger portion suffers oxidative degradation to a physio- 

 logically inactive compound tentatively designated as a phenolic 

 aminoacetophenone. 



(2) The biochemistry of the cell is altered, in at least the following ways: 

 {a) The ability of cells to destroy lAA (hereafter referred to as lAA 



oxidase activity) may be increased by pretreatment with physio- 

 logical concentrations of lAA. 

 {b) Both of the functional moieties of the lAA-oxidase complex of 

 etiolated peas, i.e. the peroxide-producing system and the peroxidase 

 which actually destroys lAA, may similarly be increased in activity 

 by pretreatment with lAA. 



■f I wish to acknowledge generous financial aid provided by the National Science Founda- 

 tion and the American Cancer Society. I am greatly indebted to the following colleagues for 

 their contributions to this work: Miss L. Dalberg, Dr. P. L. Goldacre, Dr. W. A. Jensen, 

 Dr. D. T. Manning, Dr. I. B. Pedis, Dr. P. E. Pilet, Dr. S. M. Siegel, and Dr. R. L. Weintraub. 



X Address after 1 September, 1955: Plant Science Department, Yale University, New 

 Haven, Connecticut, U.S.A. 



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