megaspore
(noun)
the larger spore of a heterosporous plant, typically producing a female gametophyte
Examples of megaspore in the following topics:
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Life Cycle of a Conifer
- Like all gymnosperms, pines are heterosporous, generating two different types of spores: male microspores and female megaspores.
- One megaspore mother cell (megasporocyte) undergoes meiosis in each ovule.
- The gametophytes (1n), microspores and megaspores, are reduced in size.
- This phase may take more than one year between pollination and fertilization while the pollen tube grows towards the megasporocyte (2n), which undergoes meiosis into megaspores.
- The megaspores will mature into eggs (1n) .
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Sexual Reproduction in Gymnosperms
- In the female cone, megaspore mother cells are present in the megasporangium.
- The megaspore mother cell divides by meiosis to produce four haploid megaspores.
- One of the megaspores divides to form the multicellular female gametophyte, while the others divide to form the rest of the structure.
- (f) Within this single ovule are the megaspore mother cell (MMC), micropyle, and a pollen grain.
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The Life Cycle of an Angiosperm
- Therefore, they generate microspores, which will produce pollen grains as the male gametophytes, and megaspores, which will form an ovule that contains female gametophytes.
- Within each megasporangium, a megasporocyte undergoes meiosis, generating four megaspores: three small and one large.
- Only the large megaspore survives; it produces the female gametophyte referred to as the embryo sac.
- The megaspore divides three times to form an eight-cell stage.
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Sporophytes and Gametophytes in Seedless Plants
- The male spores are called microspores, because of their smaller size, and develop into the male gametophyte; the comparatively larger megaspores develop into the female gametophyte.
- Heterosporous plants produce two morphologically different types of spores: microspores, which develop into the male gametophyte, and megaspores, which develop into the female gametophyte.
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Angiosperm Flowers
- The megaspores and the female gametophytes are produced and protected by the thick tissues of the carpel.
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Characteristics of Gymnosperms
- The other type of cones, the larger "ovulate" cones, make megaspores that develop into female gametophytes called ovules .
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Sexual Reproduction in Angiosperms
- First, in the process of megasporogenesis, a single cell in the diploid megasporangium undergoes meiosis to produce four megaspores, only one of which survives.
- During the second phase, megagametogenesis, the surviving haploid megaspore undergoes mitosis to produce an eight-nucleate, seven-cell female gametophyte, also known as the megagametophyte, or embryo sac.