GibberelUn-Auxin Interaction and Metabolic Basis 623 



DISCUSSION 



The significance of tlie GA-IAA synergism for the control of growth 

 in certain green tissues, and of the absence of such synergism in etio- 

 lated tissues is at present impossible to ascertain. In another article in 

 this volume, Hillman and Purves present considerable evidence that, 

 in etiolated pea tissue at least, GA and lAA operate through largely 

 independent pathways. A similar analysis has not yet been per- 

 formed for green stem tissue. 



What is the significance of these findings on peroxidase levels as 

 affected by GA? In view of the uncertainty concerning the in vivo 

 function of peroxidase, little of a definite nature can be stated. How- 

 ever, the following points seem suggestive of some significance, at 

 least, (a) The changes induced by GA on peroxidase in dwarfs are de 

 tectable at least as early as the growth effects can be noted. They 

 are therefore probably not merely distant and secondary consequences 

 of the alteration of growth by GA. (b) The simple nature of the dif- 

 ferences between the peroxidase pattern of the normal and dwarf 

 plants seems consistent with the fact that they differ in a single gene. 

 (c) The relatively simple and specific effect of GA on the peroxidase 

 pattern seems consistent with the biochemical amelioration of a simple 

 genetic abnormality. 



Considerably more work is obviously needed to assess these in- 

 teresting possibilities more adequately. 



ACKNOWLEDGMENTS 



W^e wish to express our gratitude to Miss Mary Lyons, who per- 

 formed many of the pea stem section growth experiments described 

 in the paper. We also wish to acknowledge the generous support fur- 

 nished by the National Science Foundation and the U.S. Public Health 

 Service to one of us (A. W. Galston). 



LITERATURE CITED 



1. Brian, P. W., and Hemming, H. G. The effect of gibberellic acid on shoot 

 growth of pea seedlings. Physiol. Plant. 8: 669-681. 1955. 



2. , and Hemming, H. G. Complementary action of gibberellic acid and 



auxins in pea internode extension. Ann. Bot. II. 22: 1-17. 1958. 



3. Galston, A. W. Some metabolic consequences of the administration of indole- 

 acetic acid to plant cells. In: R. L. Wain and F. Wightman (eds.). The Chem- 

 istry and Mode of Action of Plant Growth Substances, pp. 219-233. Butterworth 

 Sci. Publ., London. 1956. 



4. , and Baker, R. S. Studies on the physiology of light action. V. Photo- 

 inductive alteration of auxin metabolism in etiolated peas. Amer. Jour. Bot. 

 40: 512-516. 1953. 



5. , Bonner, J., and Baker, R. S. Flavoprotein and peroxidase as compo- 

 nents of the indoleacetic acid oxidase system of peas. Arch. Biochem. Biophys. 

 42: 456-470. 1953. 



