The Effect of the Conversion of Indolebutyric Acid into Indoleacetic Acid on Root Formation on Microcuttings ofMalus

摘要

The uptake and metabolism of tritiated indolebutyric acid (IBA) and indoleacetic acid (IAA) were related to root regeneration on stem bases of apple (Maluscv“Jork”) shootlets cultured in vitro. The major part of the auxins taken up from the medium was located in the bottom 1 mm of the stem basis, the location where the roots emerge. In this part of the shoot about 4%of the accumulated IBA-3H remained in the free acid. Analysis on normal phase TLC followed by reversed phase HPLC revealed that about 1%of the IBA-metabolites co-chromatographed with standard IAA. Incubation of shoots on medium with IAA led also to an IAAintcontent of about 1%of the amount absorbed. IAA was not converted into IBA. A medium concentration of 3.2μM IAA or IBA induced maximum root formation of 9 and 13 roots per shoot, respectively. The IAAintcontent in the stem base was 0.5μmol per kg FW after 5 days regardless of the auxin source. Incubation on medium with IBA led to an IBAintconcentration of 3.4μmol per kg FW. IBA may exert its action partly via conversion into IAA. However, the fact that IBA induced more roots than IAA suggests that IBA itself is also active, or modulates the activity of IAA.The partition of absorbed auxin over active free auxin acid and individual conjugates was not directly related to root formation. At inductive and non-inductive auxin concentrations no shift in the ratio of free auxin acids to total absorbed auxin was observed during root for