| Sumario: | The ultrastructural changes of the different parts of citrus ovules (Citrus sinensis (L.) Osbeck, cv. 'Navelate'), outer and inner integuments and nucellus during their development, and the onset of following degeneration were studied. Remarkable changes in integument cells during development and degeneration were not observed. Both outer and inner integument cells have a large central vacuole and many amyloplasts containing large starch granules. Nucellus cells are rich in cytoplasm. At anthesis, their cytoplasm contains mitochondria, small profiles of endoplasmic reticulum and abundant free ribosomes and amyloplasts with large starch granules. Fifteen days after anthesis, the onset of nucellus degeneration takes place. Inside nucellus normal cells and cells with symptoms of degeneration coexist. Degenerating cells are distinguished by shrinkage of cytoplasm, disappearance of central vacuole and mixing of the different cytoplasmic constituents.
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