LAUSR

BACKGROUND AND AIMS Branching is an important mechanism of plant shape establishment and the direct consequence of axillary bud outgrowth. Recently, hydrogen peroxide (H2O2) metabolism known to be involved in plant growth and development, has been proposed to contribute to axillary bud outgrowth. However, the involvement of H2O2 in this process remains unclear. METHODS We analyzed the content of H2O2 during bud outgrowth and characterized its catabolism, both at the transcriptional level and in terms of its enzymatic activities, using RT-qPCR and spectrophotometric methods, respectively. In addition, we used in-vitro culture to characterize the effects of H2O2 application and GSH synthesis inhibitor on bud outgrowth, in relation to known molecular markers involved in this process. KEY RESULTS Quiescent buds display a high content of H2O2 that declines when bud outgrowth is initiated, as the consequence of an increase in the scavenging activity that is associated with glutathione pathways (ascorbate-glutathione cycle and glutathione biosynthesis); catalase does not appear to be implicated. Modification of bud redox state after the application of H2O2 or BSO (inhibitors of glutathione synthesis) prevents axillary bud outgrowth by repressing organogenesis and newly-formed axis elongation. Hydrogen peroxide also represses bud outgrowth-associated marker gene expression. CONCLUSIONS These results state that high levels of H2O2 in a quiescent state prevents bud outgrowth. Induction of ascorbate-glutathione pathway scavenging activities result in a strong decrease of H2O2 content in buds, which finally allows bud outgrowth.