AbstractThe seed developmental process involves various tissues with several ploidy levels and different genetic origins. Therefore, its characterisation at the transcriptome level is certainly a challenge. The hypothesis of endosperm balance number (EBN) postulates that each species has an effective number that is important for normal endosperm and seed development to occur. Understanding endosperm formation in apomictic plants is crucial for the perspective of transferring apomixis to sexual species of agronomic interest. Since sexual tetraploid Paspalum plants fit the EBN premise, the EBN insensitivity observed in apomictic plants might be a requirement for the spread of pseudogamous apomixis. Crosses using several cytotypes of Paspalum notatum were made in order to induce the development of seeds with different maternal/paternal genomic ratios in the endosperm. A transcriptome characterisation of ovaries 3 h after pollination was performed using cDNA‐AFLP methodology. Forty‐six of the 100 differentially expressed transcript‐derived fragments (DETDFs) were specifically found in crosses in which apomictic plants were used as the female parent and presented a predicted m : p ratio in the endosperm that was different to the 2:1 requirement of the EBN. Moreover, 12 of the DETDFs presented identity with proteins that were differentially expressed in response to changes in the levels of extracellular ATP (eATP) in Arabidopsis cell suspension cultures. eATP is an important molecular switch in plants that tightly controls organellar energy metabolism and activates gene expression controlling specific growth and developmental programmes. The results suggest that eATP‐mediated signalling could be involved in the regulation of endosperm development.