Structural and histochemical studies on grain-filling in the caryopsis of rice (Oryza sativa L.).

The endosperm and embryo that constitute the filial tissues of rice caryopsis are isolated from the maternal tissues by the absence of any symplastic continuity. Nutrients are transported to the endosperm through a single ovular vascular trace present on the ventral side of the ovary. Initially solute enters through the chalaza into the nucellar projection and then into the endosperm. At later stages transport occurs through the nucellar epidermis, centripetally towards the endosperm. The cell walls of the nucellar epidermis are provided with rib-like thicken ings. A comparison of grain-filling in C3 and C4 cereals suggests that rice has structural features allied to C3 cereals, such as wheat, but with significant differences.