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#megasporogenesis

3 public questions tagged with this topic.

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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plant Development - 1

Megasporogenesis results in formation of:

Megasporogenesis occurs within ovule nucellus where subepidermal archesporial cell enlarges into megaspore mother cell undergoing meiosis I and II producing linear tetrad of four haploid megaspores with distinct animal-vegetal polarity. Three megaspores positioned toward micropyle undergo programmed cell death degenerating completely, while chalazal-most megaspore located near nutrient supply survives as functional megaspore. This selective survival establishes female germline lineage. Functional megaspore subsequently undergoes megagametogenesis involving three consecutive free nuclear mitoses without cytokinesis generating eight-nucleate embryo sac representing highly reduced female gametophyte generation.

Ref: Reiser & Fischer, Plant Cell 1993; Yadegari & Drews: megasporogenesis yields one large functional megaspore, three degenerate.

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