Fig. 7. Proposed model for BETL specification in wild-type and glo1-1 syncytial endosperms. BETL specification of basal nuclei most probably occurs via positional information by unknown cue(s) either ascending from the maternal tissue (red circles), or already present in the syncytium (green circles), or derived from both. Given the abnormal arrangement of glo1-1 basal nuclei, perhaps not all of them would perceive the positional information to assume BETL identity (blue), hence some nuclei would remain undifferentiated (yellow). Furthermore, we speculate that BETL specification is a determined event (see Discussion); hence, subsequent daughter cells would develop in a lineage-dependent fashion. Broken line indicates endosperm-maternal tissue interface.