Morphological development of the endosperm epidermal cells in waxy wheat cultivars

Endosperm epidermal cells (EECs) accumulate large quantities of nutrients; they also play key roles in facilitating solute transport. Comprehensive knowledge about the dynamic development of EECs is needed to understand the relationship between their dual functions. In this study, the developmental characteristics of EECs in wheat grains of two near-isogenic lines (Shimai19-P and Shimai19-N) and in the parent wheat cultivar Shimai19 were compared using light and scanning electron microscopy. The intermediate EECs located adjacent to the nucellar projection (NP) on the ventral surface of wheat grains rapidly differentiated. Eight days after pollination (8 DAP), these EECs were larger in Shimai19-N than in the other wheat cultivars; they had differentiated into endosperm transfer cells (ETCs). At 14 DAP, the number of ETCs reached a maximum and then gradually decreased in all three wheat varieties. The lateral ETCs and the ETCs on both sides of the crease were longer than ACs; they reached their maximum length at 16 DAP, becoming gradually shorter thereafter. The dorsal ACs became increasingly thicker during wheat grain development. Overall, these results suggested that EECs near the EC and crease are important for efficient nutrient transport, whereas EECs in other regions of wheat grains mainly play a role in nutrient storage.