Structural Differentiation of the Nucellar Epidermis in the Caryopsis of Rice (Oryza sativa)

Abstract

In the developing caryopsis of rice (Oryza sativa L.) the nucellar epidermis forms a uniseriate layer through which assimilates are transported to the endosperm. An anatomical study demonstrated that the nucellar epidermal cells are fusiform in shape and are hexagonally packed. The anticlinal walls of the nucellar epidermis are characterized by ribs of wall-thickening which are orientated radially with respect to the caryopsis. The wall-thickenings appear to be cellulosic primary walls, as indicated by their staining with Calcofluor and periodic acid-Schiff's reagent. It is proposed that the geometry of the nucellar cells and the ribs of wall-thickening are structural adaptations to resist the compressional force which is placed on the nucellar epidermis during the latter stages of grain filling.