p. W. BRIAN 



and 



H. G. HEMMING 



Imperial Chemical Industries 

 England 



Interaction of Gibbereltlc Acid and Auxin In 



Extension Growth of Pea Stems 



The garden pea (Pisum sativum) is an excellent plant for study of the 

 role of gibberellins in internode extension. Of particular interest are 

 comparisons of tall and dwarf varieties and comparisons of intact 

 internodes with internode sections floating on substrate solutions. The 

 following observations have been made in the course of our work on 

 this plant (3,4): 



(a) The rate of internode extension in tall varieties of pea is far 

 greater than that in dwarfs, yet sections from comparable internodes 

 of tall and dwarf varieties extend at approximately the same rate, 

 whether incubated in plain buffer or in solutions containing sucrose 

 or indole-3-acetic acid (lAA). The rate of extension of sections on 

 lAA/sucrose in short-term experiments is much greater than that of 

 comparable tissues in intact dwarfs, but nearly the same as that of 

 internode tissues in intact tall varieties. 



(b) Though intact dwarf pea plants give a great response to ex- 

 ogenous gibberellic acid (GA), the response of sections is small, and 

 only demonstrable in the presence of an auxin. 



(c) Intact dwarfs give a much greater response to GA than intact 

 tall peas, yet sections from both kinds respond to nearly the same 

 extent. 



These observations indicate that the difference in growth rate be- 

 tween the tall and dwarf varieties is not determined in the internode 

 tissue but elsewhere; similarly, the differential response of tall and 

 dwarf peas to exogenous GA is not due to an innate difference in 

 competence of their internode tissues. Indeed, we have evidence that 

 the apical bud is of great importance in this connection. However, we 

 have taken the view that detailed knowledge of the factors governing 



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