Structure-activity relationship of naturally occurring strigolactones in Orobanche minor seed germination stimulation

Eleven naturally occurring strigolactones (SLs) were examined for their germination-stimulating activity on the seeds of a root parasitic plant Orobanche minor Sm. Based on their activity, SLs are classified into 3 groups (A-C). Group A, the most active germination stimulant, consists of 3 monohydroxy-SLs, orobanchol, 2'-epiorobanchol, and sorgomol, inducing >80% germination of O. minor seeds at 10 pM. Group B includes 5 SLs, which were ca. 10-fold less active than those in group A. The 3 least active SLs in group C were either more lipophilic or probably less stable than SLs in groups A and B. These results indicate that the germination-stimulating activity of SLs depends on the lipophilicity of the SL molecules and their stability also influences activity. Other structural features for germination-stimulating activity are also discussed. (C) Pesticide Science Society of Japan