Levels of endogenous indole-3-acetic acid and indole-3-acetyl-aspartic acid during adventitious rooting in avocado microcuttings

Abstract

Quantification of endogenous IAA and lAAsp was carried out during adventitious root formation in avocado microcuttings. Both auxin and conjugate were monitored in control cuttings (rooted in the absence of auxin) as well as in cuttings treated with a rooting promotor (IBA) or an auxin transport inhibitor (TIBA). Additionally, a histological study to follow root differentiation was carried out. In control cuttings IAA levels remained constant throughout the rooting process, however, in IB A-treated cuttings IAA levels increased 2-fold during the first 6 d. Addition of 200 fit* TIBA induced a slight decrease of IAA levels and inhibited root formation. As for lAAsp levels, both control and IBA-treated cuttings showed a big increase before root differentiation occurred and as the process went on, a progressive decrease took place. However, in TIBA-treated cuttings lAAsp levels not only did not increase but diminished progressively during the process. The role of auxin conjugates during the rooting process of avocado is discussed.

Micropropagation of Avocado (<i>Persea Americana</i> Mill.)

“…In a rooting experiment by Barrera-Guerra, Ramirez-Malagon, and Martinez-Jaime [7], juvenile shoots have shown much higher rooting potential except for the shoots raised in Among all plant growth regulators, auxins play an essential role in root induction process of plants. Proving it is no difference with avocado, García-Gómez et al [59] showed that auxin transport inhibitor 2,3,5-triiodobenzoic acid completely inhibited root primordia differentiation of juvenile avocado micro cuttings in vitro. Therefore, exogenous supply (specific type and concentration) of auxin is paramount in rooting avocado shoots.…”

“…Another auxin 2-4-dichlorophenoxyacetic acid (2,4-D) has been toxic even at very low concentrations [67], and not frequently used for rooting avocado. IAA is a naturally occurring auxin in plants and has low stability when exposed to light and high temperature [59]. A comparison of IBA vs NAA for rooting (juvenile material)…”

Distribution of indole-3-acetic acid in Petunia hybrida shoot tip cuttings and relationship between auxin transport, carbohydrate metabolism and adventitious root formation

“…For example, decapitation and treatment of pea stem cuttings with NPA led to the reduction in IAA levels in cutting bases during the first days after excision, which was associated with lower numbers and shorter lengths of ARs (Nordström and Eliasson 1991; Koukourikou-Petridou and Bangerth 1997). Similarly, application of TIBA to avocado cuttings inhibited the differentiation of root primordia and reduced the percentage of rooted cuttings, while the IAA level in the basal stem was only slightly reduced (Garcia Gomez et al 1994). These studies did not demonstrate a significant increase of IAA in the stem base of non-treated control cuttings, although they did produce a high number of roots.…”

“…One way to reduce active auxin is degradation via oxidative decarboxylation, which is probably associated with one of the important functions of higher peroxidase activity repeatedly observed after the induction phase (Kevers et al 1997; Tonon et al 2001). Another way to reduce the level of active auxin is by conjugation to sugars and amino acids (Woodward and Bartel 2005), which may be indicated by an increased levels of IAA conjugates such as indole-3-acetylaspartic acid (IAAasp) during later stages of AR formation (Nordström and Eliasson 1991; Garcia Gomez et al 1994). In this respect, auxin-inducible GH3 (Gretchen Hagen 3) genes can play an important role in the control of free auxin levels because specific GH3 s can catalyse conjugation of amino acids to IAA (Staswick et al 2005; Wang et al 2007).…”

“…These studies did not demonstrate a significant increase of IAA in the stem base of non-treated control cuttings, although they did produce a high number of roots. Because a transient increase in the level of IAAasp was detected in the basal part of untreated cuttings, the authors speculated that the initial IAA level could be sufficient to induce ARs or that a steady but non-detected release of IAA from IAAasp possibly contributed to AR formation (Nordström and Eliasson 1991; Garcia Gomez et al 1994). However, Blakesley et al (1991) detected a sharp peak of IAA in hypocotyls of Phaseolus aureus already within the first 10-h post excision.…”