Brassinosteroid-Driven Stimulation of Shoot Formation and Elongation: Application in Micropropagation

Brassinosteroids (BRs) comprise a specific class of low-abundance, natural polyhydroxy steroidal lactones and ketones now recognized as a new class of phytohormones. These steroids of ubiquitous occurrence in plants are known to stimulate stem elongation and to control apical dominance as well. In this chapter, we describe the use of BRs to significantly improve protocols for micropropagation of woody species, more specifically, the marubakaido apple rootstock and a clone of Eucalyptus, through the stimulation of shoot elongation and formation of new shoots. It is also shown in this chapter that these BR-induced changes in shoot architecture do not result from changes in the endogenous levels of any single metabolite and do not rely on broad changes in the metabolite profile, as well.