Development of the endosperm in rice (Oryza sativa L): Cellularization

The syncytial endosperm of rice undergoes cellularization according to a regular morphogenetic plan. At 3 days after pollination (dap) mitosis in the peripheral syncytium ceases. Radial systems of microtubules emanating from interphase nuclei define nuclear-cytoplasmic domains (NCDs) which develop axes perpendicular to the embryo sac wall. Free-growing anticlinal walls between adjacent NCDs compartmentalize the cytoplasm into open-ended alveoli which are overtopped by syncytial cytoplasm adjacent to the central vacuole. At 4 dap, mitosis resumes as a wave originating adjacent to the vascular bundle. The spindles are oriented parallel to the alveolar walls and cell plates formed in association with interzonal phragmoplasts result in periclinal walls that cut off a peripheral layer of cells and an inner layer of alveoli displaced toward the center. Polarized growth of the newly formed alveoli and elongation of the anticlinal walls occurs during interphase. The next wave of cell division in the alveoli proceeds as the first and a second cylinder of cells is cut off inside the peripheral layer. The periods of polarized growth/anticlinal wall elongation alternating with periclinal cell division are repeated 3-4 times until the grain is filled by 5 dap.