Development of Megasporocyte in the ovary of a mature ovule:
The ovule is a large parenchymatous body (nucellus) that is formed in the ovary. The stalk of the ovule is called funiculus and is attached to the ovary by the placenta. The ovule is surrounded by one or two protective layers called integuments, leaving a small opening at one end termed as a micropyle. The basal part of the ovule where nucellus, integuments and funicle merge is called as chalaza. The development of the megaspore within the ovule is called as megasporogenesis.
The ovule is composed of a multilayered cellular tissue called the nucellus. A hypodermal cell of the nucellus at the micropylar end differentiates and becomes transferred into a megaspore mother cell. Each diploid megaspore mother cell undergoes meiosis to form a tetrad of haploid megaspores. Three megaspores degenerate and remaining functional one enlarges at the chalaza end.
The functional megaspore undergoes three subsequent divisions and forms the eight nuclei. The eight nuclei arrange themselves into three groups. Three nuclei migrate at the micropyle end and form the egg apparatus, consisting of two synergids and a round egg cell. The other three nuclei arrange themselves at the chalaza end and form the antipodal cells. The remaining two nuclei come together as polar nuclei in the centre of the embryo sac. All the cells of the embryo sac are haploid except the polar nuclei which are diploid.
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