A. C. LEOPOLD 



and 

 S. L. LAM 



Purdue University 



Polar Transport of Three Auxins' 



In understanding the polar system which transports auxin through 

 plants, it is particularly relevant to know whether the transport sys- 

 tem is specific to indole-3-acetic acid (I A A). There is evidence in the 

 earlier literature that some other auxins may be carried in the trans- 

 port system (10), but it is not clear whether these compounds may all 

 be moved with the same polarity and the same velocity as indole-3- 

 acetic acid, nor is it clear how effectively the transport system can 

 distinguish between auxins of different molecular structure. Experi- 

 ments on these questions were undertaken in an effort to characterize 

 further the polar transport system in plants. 



METHODS 



The auxins were assayed in every case by means of the Avena cur- 

 vature test, following the procedure described by Leopold (4). 



The auxins were transported through stem sections taken from 

 the epicotyl of sunflower seedlings grown in the greenhouse between 

 December and April. The method is identical to that described by 

 Niedergang-Kamien and Leopold (6). A donor block was placed at 

 the apical end of a 5 mm. stem segment, and the auxin transported 

 into a receptor block at the basal end was assayed after 120 min. of 

 transport at 25° C. Unless otherwise indicated, all transport tests 

 with indole-3-n-butyric acid continued for 180 min. 



The experiments with transport inhibitors were carried out by the 

 method of Niedergang-Kamien and Leopold (7). The inhibitor was 

 applied in an agar block at the basal end of the sunflower stem sec- 

 tion, and the auxin was simultaneously applied as a 5 /^l. droplet at 



1 Journal Paper No. 1493, Purdue University, Agricultural Experiment Sta- 

 tion, Lafayette, Indiana, U.S.A. 



[411] 



