The tiny seeds of the obligate root parasitic plants of the Orobanchaceae do not germinate unless they detect chemical signals from a suitable host plant. After crossing the two closely related species Orobanche cernua and O. cumana, Plakhine et al. find hybrid families that do not need chemical stimulation for germination. This lethal trait appears only in F3 and further generations, indicating that the dependence on external chemical stimuli is genetically controlled in the seed perisperm, which is the only seed tissue of maternal origin. The results suggest that the stimulant receptors are located in the cells of the perisperm that are located beneath the micropyle.
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