#embryo sac

plant Development - 1

Cells degrading after fertilization in embryo sac:

Following double fertilization and early embryogenesis, embryo sac undergoes extensive remodeling via programmed cell death of unnecessary attraction cells. Two synergid cells that synthesized LURE peptides guiding pollen tube usually degenerate rapidly upon tube arrival preventing additional tubes via ethylene and FERONIA-mediated polyspermy block, and antipodal cells at chalazal pole degenerate quickly after fertilization, though persist longer in cereals providing transient nutrition support. Their coordinated degradation recycles valuable nutrients and eliminates residual attraction signals, efficiently allocating maternal resources to developing embryo and triploid endosperm within maturing seed for robust offspring production.

Ref: Mathew & Prasad, Bot Rev; Drews: synergids and antipodals degrade after fertilization via programmed cell death.

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plant Development - 1

Embryo sac consists of:

Embryo sac in Polygonum-type typical of approximately seventy percent angiosperms consists of seven cells organized around eight nuclei arising from three sequential free nuclear mitoses of functional megaspore without initial cytokinesis. Configuration comprises micropylar egg apparatus with two synergids flanking egg cell, large central cell with two polar nuclei occupying huge central vacuole, and chalazal three antipodal cells often ephemeral. This precise seven-celled eight-nucleate organization positions egg for fertilization, synergids for pollen tube attraction, central cell for endosperm initiation, and antipodals for transient support or signaling during early seed development stages.

Ref: Drews & Koltunow, Arabidopsis Book 2011: typical embryo sac seven cells eight nuclei Polygonum-type organization.

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plant Development - 1

Nucellus is primarily a:

Nucellus constitutes central parenchymatous tissue of ovule derived from megasporangium forming massive bulk surrounding and protecting megaspore mother cell and later embryo sac. It serves primarily as nutritive tissue providing carbohydrates, amino acids, lipids, and hormonal cues to developing female gametophyte through apoplastic and symplastic transport pathways. Depending on crassinucellate or tenuinucellate configuration degree of tissue development may be substantial. After fertilization nucellus generally degenerates, but may occasionally persist as perisperm storage tissue in beet, pepper, black pepper, continuing important maternal nutritive contribution supporting embryo growth and seed filling.

Ref: Mohammad et al., Seed Sci; Reiser & Fischer: nucellus is nutritive tissue surrounding and feeding embryo sac.

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plant Development - 1

Angiosperm gametophytes develop from:

Angiosperm gametophytes develop from haploid spores produced within sporangia located in third and fourth floral whorls according to classical ABC model. Third whorl stamens produce microsporangia generating male gametophytes pollen grains, while fourth whorl carpels form megasporangia ovules generating female gametophytes embryo sac. First whorl sepals and second whorl petals are sterile protective and attractive structures aiding pollination and preventing desiccation. This organization directly links MADS-box floral organ identity patterning to gametophyte generation location, elegantly coordinating transition from diploid sporophyte to haploid gametophyte phase during sexual reproduction of flowering plants.

Ref: Coen & Meyerowitz, Nature; Goldberg: angiosperm gametophytes develop from third whorl anthers and fourth whorl carpels.

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Sexual Reproduction in flowering Plants

In a monosporic embryo sac development (Polygonum type), nuclear divisions are:

The mitotic divisions of the functional megaspore nucleus are strictly free nuclear, meaning nuclear division is not followed immediately by cell wall formation. Cell walls are laid down only after the 8-nucleate stage is reached, leading to the 7-celled organization.

Ref: Sequence showing 1 -> 2 -> 4 -> 8 nuclei stage before cell walls form.

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Sexual Reproduction in flowering Plants

A typical angiosperm embryo sac at maturity is described as '7-celled and 8-nucleate'. Which of the following cells are

In the embryo sac, the Egg cell, Synergids, and Antipodals are all derived from the haploid megaspore via mitosis, so they are haploid (n). The Central cell contains two polar nuclei (n+n) before fertilization. The Zygote (2n) and Primary Endosperm Nucleus (3n) are post-fertilization structures.

Ref: Diagram of a mature embryo sac showing the egg apparatus, central cell, and antipodals.

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Sexual Reproduction in flowering Plants

In the majority of angiosperms, the functional megaspore develops into the embryo sac. What is the ploidy sequence of th

The Nucellus is part of the sporophyte (2n). The Megaspore Mother Cell (MMC) differentiates from the nucellus and is also diploid (2n). The MMC undergoes meiosis to form megaspores (n). The functional megaspore (n) divides mitotically to form the female gametophyte (n).

Ref: Diagram of an ovule showing the nucellus surrounding the MMC and subsequent reduction division.

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