The fate of vitamin D3 and indolylbutyric acid applied to cuttings of Populus tremula L. during adventitious root formation

Treatment of green cuttings of Populus tremula L. with vitamin D3 enhances adventitious rooting and synergy is observed on simultaneous application with indolylbutyric acid. Translocation experiments with labelled vitamin D3 and IBA, fed to the base of the cuttings, showed that such synergy was not due to an effect of one substance on the translocation of the other. When indolylbutyric acid was fed to the base of the cuttings, a high proportion was rapidly converted into conjugates which, on saponifaction, released inter alia indolylbutyric acid, but no indolylacetic acid. On the other hand, vitamin D3 was metabolized to give products similar to those produced in non‐sterile aqueous solutions of vitamin D3 stored under the conditions of culture of the cuttings. Such a mixture is as effective as vitamin D3 itself in promoting adventitious rooting. A preliminary examination of the products showed that extensive oxidation of vitamin D3 had occurred and some of the individual components were synthesized and tested for their effect on rhizogenesis in P. tremula.