BRUCE B. STOWE^ 



Harvard University 



The StLmutatlon of Auxin Action by Llpldes 



Studies with the gibberellins have exposed a major paradox: intact 

 dwarf peas respond markedly to treatment with gibberellic acid, 

 whereas epicotyl sections cut for bioassay from similar plants respond 

 hardly at all (1,20). Thus a conventional straight growth section 

 bioassay for growth substances is almost useless for the estimation of 

 gibberellins. More importantly, this observation exposes a hiatus in 

 our understanding of the mechanism of growth in these sections, 

 and moreover, this gap seems particularly amenable to experimental 

 analysis. 



Our own measurements of the growth, under optimum conditions, 

 of dwarf peas and of the sections obtained from them are summarized 

 in Table 1 (18). It is apparent that, as has been reported by others, 

 gibberellic acid (GA3) itself has only a marginal influence on the 

 sections; more significant is its further promotion of the effect of 

 indole-3-acetic acid (I A A). Even so, the sections under these optimal 

 conditions are not even two-thirds of the length they would have 

 reached on the intact plant, and only one-third of the length they 

 would have achieved with GA3 treatment. 



A likely explanation of this growth deficiency is that some factor 

 required for gibberellin action is normally supplied to the section 

 by the rest of the plant. In previous work (16) we found that a fat 

 fraction could be isolated from peas which markedly promoted sec- 

 tion growth, and it was natural to test this for its ability to restore 

 part of this missing growth. This fat fraction was not a specific sub- 

 stance, however, as a wide variety of fatty acid esters could also in- 

 crease the growth obtained. 



1 Subsequently: J. W. Gibbs Laboratory, Department of Botany, Yale Uni- 

 versity, New Haven, Conn. 



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