Figure 1.

Lettuce achenes are highly sensitive to KAR₁. A, Structures of KAR₁, KAR₂, GR24^ent-5DS, and GR24^5DS. GR24^5DS is a strigolactone analog that mimics the stereochemical configuration of the SL 5-deoxystrigol. GR24^ent-5DS is an enantiomer of GR24^5DS that has a methylbutenolide D-ring in 2′S configuration, which is not found in natural SLs. B, Lettuce germination in the presence of 0.1% (v/v) acetone or 1-µM KAR₁, KAR₂, or rac-GR24. Achenes were incubated 1 h in darkness, followed by a pulse of far-red light for 10 min, and the remaining 48 h in darkness at 20°C. n = 4 replicates of ∼50–70 achenes each; mean ± sd. C, Lettuce germination in the presence of a range of KAR₁ and KAR₂ concentrations after 1 h in darkness, followed by a pulse of far-red light for 10 min, and the remaining 48 h in darkness at 20°C. n = 3 replicates of ∼50–60 achenes each. D) RT-qPCR analysis of LsDLK2 expression relative to LsACT (actin) in lettuce achenes imbibed with 0.1% (v/v) acetone or 1-µM KAR₁, KAR₂, or rac-GR24 for 24 h in darkness at 20°C. n = 4 pools of achenes; mean ± sd. Values re-scaled to relative LsDLK2 expression in mock-treated achenes.