Since auxin is unable to enter in t

Since auxin is unable to enter in the bud, some authors suggest that the basipetal flux of auxin inhibits auxin export from the axillary buds and consequently their outgrowth (Bennett et al.,
2006; Prusinkiewicz et al., 2009). An alternative hypothesis sug- gests that auxin inhibits bud outgrowth through the action of a second messenger, which is able to enter the bud, although the antagonistic effects of cytokinins and strigolactones that respec- tively promote or inhibit bud outgrowth (Tanaka et al., 2006; Gomez-Roldan et al., 2008; Brewer et al., 2009). Auxin regulates the synthesis of cytokinins at the node by down-regulating the gene coding for adenylate isopentenyl transferase (IPT), which is, in turn, implicated in cytokinin biosynthesis (Tanaka et al., 2006). Auxin also regulates the synthesis of strigolactone by up-regulating tran- scription of genes encoding proteins implicated in strigolactone biosynthesis (Johnson et al., 2006).