ON THE MANNER OF TRIIODOBENZOIC ACID INHIBITION OF AUXIN TRANSPORT

The effects of 2, 3, 5-triiodobenzoic acid on the transportof indoleacetic acid by corn coleoptile sections were examinedrelative to the entry and exit components of the transport system.The TIBA inhibition of IAA entry was found to be relativelyweak, requiring about 1,000-fold higher concentrations thanthe inhibition of exit. The preferential inhibition of exitcan account for the accumulation of IAA in TIBA-inhibited tissuesections. The kinetics of the TIBA inhibitions indicate markedlydifferent characteristics of the entry and exit components,and implicate exit as a rate-limiting step in the auxin transportmechanism. ¹Present address: Research Division, Ontario Water ResourcesCommission, Toronto, Canada