412 



A. C. Leopold and S. L. La 



m 



the apical end. After 30 min. the stem section was blotted and trans- 

 ferred to a fresh receptor block in which the transported auxin was 

 collected for an additional 90 min. In these experiments, the con- 

 trols were transferred from a plain agar block to a fresh receptor block 

 at the same time that the inhibitor treatments were transferred. This 

 represents the only modification of the earlier technique. 



RESULTS 



Preparatory to a comparison of the transport of several different 

 auxins, five auxins were tested for activity in the Avena curvature 

 test. Included in this test were indole-3-acetic acid (lAA), 1-naphtha- 

 leneacetic acid (NAA), indole-3-n-butyric acid (IBA), indole-3-propi- 

 onic acid (IPA), and 2-naphthoxyacetic acid (NOA). Characteristic 

 Avena test data for these five auxins are shown in Figure 1. Of course 

 the greatest curvature response was obtained with lAA. Normal cur- 

 vature responses were also obtained with NAA and IBA, though less 

 curvature was obtained with these per unit of auxin. IPA and NOA 

 yielded essentially no curvatures. 



The Avena curvature test is, therefore, a valid assay for the three 

 auxins: lAA, NAA, and IBA. 



The transport of these three auxins in both basipetal and acrope- 



10 



10"' 10'=" 



MOLAR CONCENTRATION OF AUXIN 



10" 



Fig. 1. Response curves for five auxins in the Avena curvature test: indole-3- 

 acctic acid (IaA), indolc-3-n-butyric acid (IBA), 1-naphthaleneacctic acid (NAA), 

 indole-3-propionic acid (IPA), and 2-naplulioxyacctic acid (NO.^). 



