Translocation of Shoot‐Applied Indolylacetic Acid into the Roots of Populus tremula

Abstract

AbstractApplication of 10 to 100 μg indol‐3‐ylacetic acid to the leaves of rooted cuttings of aspen caused inhibition of root growth after three hours. Root growth recovered within 24 hours after IAA treatment. Swelling of the root tips occurred during the period of inhibition. The roots responded in the same way if IAA was applied in solution to the cut stem surface above the mature leaves.IAA‐1‐14C applied through a cut stem surface or to mature leaves was translocated downwards in the plants and labelled IAA could be isolated from the roots 3 to 24 hours after application. The ethanol‐soluble activity decreased rapidly indicating a rapid metabolism or binding of IAA. IAA‐1‐14C applied to growing leaves was not translocated.From the rapid response of root growth it was concluded that IAA was translocated into the roots at a rate of about 7 cm per hour. This rate of translocation indicates that the sieve tubes are involved in the translocation. Implications of the results for the translocation of endogenous auxin into the roots are discussed.