Hormonal control of shoot branching

Abstract

Shoot branching is the process by which axillary buds, located on the axil of a leaf, develop and form new flowers or branches. The process by which a dormant bud activates and becomes an actively growing branch is complex and very finely tuned. Bud outgrowth is regulated by the interaction of environmental signals and endogenous ones, such as plant hormones. Thus these interacting factors have a major effect on shoot system architecture. Hormones known to have a major influence are auxin, cytokinin, and a novel, as yet chemically undefined, hormone. Auxin is actively transported basipetally in the shoot and inhibits bud outgrowth. By contrast, cytokinins travel acropetally and promote bud outgrowth. The novel hormone also moves acropetally but it inhibits bud outgrowth. The aim of this review is to integrate what is known about the hormonal control of shoot branching in Arabidopsis, focusing on these three hormones and their interactions.

Hormonal Regulation of Branching in Grasses

“…Once axillary buds have initiated, the outgrowth of axillary buds is under hormonal as well as environmental control (Ongaro and Leyser, 2008). Apical dominance is a well-known phenomenon in which auxin traveling basipetally from the shoot apex suppresses the outgrowth of axillary buds (Thimann and Skoog, 1933;Leyser, 2003;Fig.…”

“…Cytokinin was a good candidate for the second messenger, as cytokinin travels from the root to the shoot and enters the bud where it promotes outgrowth ( Fig. 3; Ongaro and Leyser, 2008), and auxin has been shown to inhibit cytokinin biosynthesis (Nordstrom et al, 2004;Tanaka et al, 2006). However, there is also evidence that cytokinin acts independently of auxin (Chatfield et al, 2000).…”

“…A novel compound required for regulation of branching was proposed based on the identification of the more axillary meristem (max) mutants in Arabidopsis, ramosus (rms) mutants in pea (Pisum sativum), and decreased apical dominance (dad) mutants in petunia (Petunia hybrida; Beveridge, 2006;Ongaro and Leyser, 2008; Table II). Grafting experiments demonstrated the existence of a long-distance signal traveling from the root, that instead of promoting outgrowth like cytokinin, suppressed outgrowth like auxin (Fig.…”

Potencial de inibição da regeneração de raízes e plântulas em sementes germinantes de Eugenia pyriformis

“…A mobilização e o transporte de muitos reguladores vegetais foram amplamente estudados em diversos tecidos, inclusive nas sementes, mas concentram-se nos promotores de divisão e crescimento celular (Hirose et al, 2008;Ongaro & Leyser, 2008;Jeong et al, 2011). Porém, pouca atenção tem sido dada aos inibidores.…”

Strigolactones as mediators of plant growth responses to environmental conditions

“…35 Alternatively, it was suggested that SLs inhibit polar auxin transport from the buds by reducing the capacity for such transport from the apical meristem, resulting in restrained bud outgrowth (reviewed in ref. 29,[36][37][38]. However, to support this last notion it still remains to be demonstrated that the timing of auxin transport out of a bud is causal to the bud outgrowth, rather than its result.…”