A. W. GALSTON 

 and 



D. C. McCUNEi 



Yale University 



An AnatysLS of GibbereltLn- Auxin Interaction 



and Its Possible Metabolic Basis 



It has now become clear that in plant tissues which respond both to 

 gibberellin and to auxin, several kinds of interactions are possible be- 

 tween these compounds. In such objects as the sub-apical etiolated 

 pea epicotyl section, the growth increment produced by a joint ap- 

 plication of the two substances is usually considerably less than, and 

 never significantly more than, the expected sum of the growth in- 

 crements produced by the separate administration of these com- 

 pounds (7, 18). On the other hand, in such objects as the sub-apical 

 green pea stem section (1,7), the sweet potato petiole (14), fruit cells 

 (15, 21), and in starved or otherwise pretreated etiolated tissues (7, 

 9, 24) a true supra-additivity or synergism has been reported to exist 

 between the growth effects produced by these compounds. In view of 

 the fact that several theories of auxin-dependent gibberellin action 

 have been proposed (1,7), it seemed desirable to analyze this situation 

 more systematically in a single plant tissue, to attempt to determine 

 the conditions under which synergistic interaction occurs. This has 

 been a major aim of the work here described. In brief, we, and Purves 

 and Hillman (19) of this laboratory, have found, in contrast with 

 previously published reports (7, 9, 24), that etiolated pea tissue, no 

 matter how pretreated, does not show a synergistic interaction between 

 auxin and gibberellin. On the other hand, green pea stem tissue de- 

 rived from plants grown under 8-hr. daily photoperiods almost in- 

 variably manifests a marked synergism. Prolongation of the dady 

 duration of illumination to 16.5 or 24 hrs. of high light intensity re- 

 sults in a diminution or even a disappearance of this synergism, ex- 

 cept under special conditions. 



iPredoctoral fellow of the National Science Foundation. The work on peroxi- 

 dases constitutes a portion of a Ph.D. thesis submitted by D. C. McCune to the 

 Graduate School of Yale University in June 1960. Subsequently: Boyce Thompson 

 Institute for Plant Research, Inc., Yonkers, N. Y. 



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