Molecular Specificity of Haustorial Induction in Agalinis purpurea (L.) Raf. (Scrophulariaceae)

An exogenous signal normally contained in host root exudateis required for initiation of the haustorium by the root parasiteAgalinis purpurea (L.) Raf. (Scrophulariaceae). Two flavonoidsthat induce haustoria have been isolated from gum tragacanthand a number of structural analogues have been synthesized.The results show that a high degree of molecular specificityis required for haustorial induction. Both isolated flavonoidscontain substituted 3-methoxyphenol functionality, and syntheticanalogues have shown that 4-substituted 3-methoxyphenol functionalityis critical for high levels of haustorial induction. These dataprovide a model for understanding host recognition at the levelof haustorial induction in parasitic angiosperms. Agalinis purpurea (L.) Raf. Scrophulariaceae, haustorial induction, flavonoids, molecular specificity, parasitic angiosperms, xenognosin