Growth Regulators in Populus tremula I. Distribution of Auxin and Growth Inhibitors.

The content of acid ether-soluble auxins and inhibitors in vegetative tissues of aspen (Populus tremula L.) was determined with the Avena coleoptile straightgrowth assay. A growth promotor, tentativety identified as indol-3-yl-acetic acid, occurred in highest concentration in the growing stem parts. It was also detected in various parts of the roots. Large amounts of inhibitors (inhihitor β) were found in growing stem tissue and in upper mature stem parts. Considerably lower content of inhibitors was found in leaves, in the basal stem part and in the roots. Nonwoody growing roots and the wood of older root segments, especially, contained very smalt quantities of inhibitors. The elution volume of a part of the inhibitory activity on a Sephadex column was similar to that of abscisic acid.