Species-specific interaction of EA1 with the maize pollen tube apex.

The egg apparatus-secreted polymorphic EA 1 peptide is required for micropylar pollen tube (PT) guidance in maize, the last step of the PT journey during the double fertilization process in flowering plants. In a recent study we have shown that maize PTs are attracted in vitro by EA 1 and that their growth is arrested at high peptide concentrations. Moreover, we have also shown that maize PTs are guided in vitro in a species-preferential manner to the micropylar opening of transgenic Arabidopsis ovules secreting the EA 1-GFP fusion protein. In support of these findings, we have improved the ligand-receptor labeling assay and report here that the EA 1 peptide interacts in vitro with the maize PT apex in a species-specific manner. Bound peptide gets internalized in large vesicles and is degraded. This finding indicates that the pollen tube remains sensitive to the attractant by its rapid internalization.