Interactions between Axillary Branches of Arabidopsis

Abstract

Studies of apical dominance have benefited greatly from two-branch assays in pea and bean, in which the shoot system is trimmed back to leave only two active cotyledonary axillary branches. In these two-branch shoots, a large body of evidence shows that one actively growing branch is able to inhibit the growth of the other, prompting studies on the nature of the inhibitory signals, which are still poorly understood. Here, we describe the establishment of two-branch assays in Arabidopsis, using consecutive branches on the bolting stem. As with the classical studies in pea and bean, these consecutive branches are able to inhibit one another's growth. Not only can the upper branch inhibit the lower branch, but also the lower branch can inhibit the upper branch, illustrating the bi-directional action of the inhibitory signals. Using mutants, we show that the inhibition is partially dependent on the MAX pathway and that while the inhibition is clearly transmitted across the stem from the active to the inhibited branch, the vascular connectivity of the two branches is weak, and the MAX pathway is capable of acting unilaterally in the stem.

Strigolactones enhance competition between shoot branches by dampening auxin transport

“…According to the canalisation model, basal auxin sources can also be effective competitors, as the auxin exported by these buds into the stem can still reduce flux from more apical auxin sources ). Indeed we have previously shown that when Arabidopsis bolting stem segments carrying two cauline leaves with their associated buds are excised, one bud often outgrows the other, and it can be either the basal bud or the apical bud that dominates (Ongaro et al, 2008). In similar two-node segments from max mutants, the two buds grow more evenly, consistent with reduced competition between the buds.…”

“…Bud hormone response assays were performed as described by Chatfield et al (Chatfield et al, 2000) for axenically grown plants, and by Ongaro et al (Ongaro et al, 2008) for soil-grown plants. For long-term auxin treatments, the synthetic auxin NAA was used because of the instability of the natural auxin, IAA.…”

Using Arabidopsis to Study Shoot Branching in Biomass Willow

“…buds, allowing the central bud to establish PATS into the main stem more rapidly. Apart from competition between the three buds, the rapidity for PATS establishment is likely further compromised by the presence of two competing auxin sinks near the buds, namely the leaf trace and the PATS in the main stem (Ongaro et al, 2008). To reduce the complexity of this system and increase the importance of bud-bud competition, GR24 delivery to the leaf trace was reduced by sealing it with lanolin, inhibiting transpiration (Fig.…”

“…buds and allowing the central bud rapidly to dominate and activate. Ongaro et al (2008) showed that buds could form vascular connections with either the leaf trace or the main stem vascular bundles. If GR24 treatment is enhancing the competitive advantage of the central Salix spp.…”

“…This is expected because auxin exported from the apical bud and transported down the stem in the PATS can easily influence the auxin sink strength of the stem at the position of the basal bud, whereas the influence of auxin exported from the basal bud on the apical bud is likely to be less strong. In Arabidopsis, the basal bud in two-node assays is able to dominate, possibly because it is typically larger than the apical bud at the start of the assay and, therefore, at a competitive advantage (Ongaro et al, 2008;Crawford et al, 2010;Liang et al, 2010). The apical Salix spp.…”