The central cell is the binucleate cell of the angiosperm megagametophyte which contains the polar nuclei and participates in double fertilization. The structure of the mature central cell, the fusion of the polar nuclei and the primary endosperm nucleus were studied with the electron microscope. The central cell cytoplasm appears very active and has an extensive ER, many mitochondria, dictyosomes, microbodies, polysomes, chloroplasts with well developed grana and starch and lipid reserves. A single, giant mitochondrion appears in the cytoplasm near the polar nuclei at the time of fertilization, but its origin, fate and function are not known. Cytoplasmic aggregates of dense, granular material are associated with the primary endosperm nucleus and structurally resemble the nucleolus and similar aggregates in the nucleoplasm. It is suggested that these cytoplasmic perinuclear bodies may represent extruded nucleolar material. The central cell cytoplasm does not undergo any notable structural reorganization as a result of fertilization. The relationship of the central cell to the other cells of the mature megagametophyte and its possible role in embryogenesis is discussed.

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