Strigolactones (SLs) are carotenoid-derived terpenoid lactones (Matusova et al. 2005). ey were identied 40 years ago as germination stimulants for the parasitic plants Striga and Orobanche (e.g., Cook et al. 1966, 1972; Yokota et al. 1998; Matusova et al. 2005; Akiyama and Hayashi 2006; Xie et al. 2007, 2008a,b, 2009; Goldwasser et al. 2008; Gomez-Roldan et  al. 2008; recently reviewed by Xie et al. 2010) and later, as stimulants of hyphal branching of the symbiotic arbuscular mycorrhizal fungi (AMF; reviewed by Xie et al. 2010). More recently, SLs have been found to act as long-distance branching factors that suppress growth of preformed axillary buds (Gomez-Roldan et al. 2008; Umehara et al. 2008). us, they t the characteristics of a novel branchinhibiting signal acting as a long-distance signal transmitter (e.g., Gomez-Roldan et al. 2008; Umehara et al. 2008; Brewer et al. 2009; Ferguson and Beveridge 2009; reviewed by Dun et al. 2009). SLs or their derivatives have therefore been dened as a new group of plant hormones.