Experiment on regeneration of apple roots from 0.5mm thick, fresh weight 1 mg shoot slices. Roots were regenerated synchronously, without an intermediate stage of callus formation and without interference with compounds derived from other parts of the plant. Application of indole butyric (IBA) or indolylacetic (IAA) acid caused a maximum average of 8 or 4.5 roots per slice, respectively. After IBA uptake a high degree of coupling led to a recovery of 2.5% as internal free IBA (about 2 times the average concentration). Due to the conversion of absorbed IBA to IAA a fraction of 0.4% was recovered as (physiologically active) free IAA. After incubation in IAA medium, 0,5 % of the absorbed hormone was recovered as free acid. No conversion of IAA to IBA was observed. The isomolar contents of the internal free IAA after incubation in IBA or IAA resulted in IBA in a greater number of radicals than in IAA. This implies that IBA may also act through internal free IBA or may synergistically modify the activity or endogenous synthesis of IAA.
Our colleague Dimitra Mavridou participated in the experiment.