Studies of indole-3-butyric acid to indole-3-acetic acid conversion in hazelnut shoot tissuee

Abstract

Indole-3-butyric acid (IBA) is an endogenous compound that appears to regulate both lateral and adventitious root formation in many plant species and is also the auxin most available commercially for application to promote rooting. IBA is converted to indole-3-acetic acid (IAA) by beta oxidation in the peroxisomes. This process has been observed in a number of plant species and has been shown to be critical for normal root development in response to treatment with IBA. In this thesis, the process was investigated in hybrid hazelnuts (C. americana x C. avellana) and American elm (Ulmus americana), in which adventitious rooting is a major bottleneck for vegetative propagation and the efficacy of IBA treatment is highly variable across different cultivars. Using differentially stable isotope labeled IBA and IAA tracer and internal standard, respectively, and using gas chromatography coupled with selected reaction monitoring mass spectrometry, IBA-derived IAA was measured in shoot tissue treated with stable isotope labeled IBA. Variable levels of IBA-to-IAA conversion were observed across different hybrid hazelnut genotypes, which may partially explain differences in rooting ability. In elm, higher levels of IBA-to-IAA conversion were observed in cultivars which formed adventitious roots most easily in softwood stem cutting trials. High rates of root formation is a key trait for establishment of large-scale production systems. Screening for optimal rates of IBA-to-IAA conversion may facilitate selection against genotypes which respond poorly to exogenous IBA. Such genotypes are difficult to propagate using hormone treatment and thus can be eliminated from further evaluations.