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Meiosis of megaspore mother cell (Angiosperms)

Meiosis of megaspore mother cell (Angiosperms). pistil contains the megaspore (2 n ) mother cell meiosis yields 4 haploid (1 n ) gametic cells (3 usu. die) 3 mitoses yield 8 (1n) nuclei in the embryo sac. Meiosis of microspore mother cell (Angiosperms).

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Meiosis of megaspore mother cell (Angiosperms)

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  1. Meiosis of megaspore mother cell(Angiosperms) • pistil contains the megaspore (2n) mother cell • meiosis yields 4 haploid (1n) gametic cells (3 usu. die) • 3 mitoses yield 8 (1n) nuclei in the embryo sac

  2. Meiosis of microspore mother cell(Angiosperms) • stamens contain microspore (2n) mother cells • meiosis yields 4 haploid (1n) microspores • the tetrad of microspores are released as mature pollen grains • 2 mitoses yield 3 (1n) nuclei (1 vegetative, 2 sperm nuclei from mitosis of the generative nucleus)

  3. Pollination and double fertilization(Angiosperms) • 1 sperm nucleus fuses with 2 polar nuclei to yield the 3n endosperm • the other sperm nucleus fuses with the egg nucleus to form the 2n zygote

  4. Stages of seed development • I. Histodifferentiation (embryo differentiation) • II. Cell expansion • III. Maturation drying

  5. I. Histodifferentiation (embryo differentiation) • cell divisions and differentiation form the embryo and endosperm • the embryo reaches the cotyledonary stage • Differentiation differs among dicots, monocots, gymnosperms • sexual and apomictic embryos develop differently

  6. Apomixis • defn: the production of an embryo that bypasses the usual process of meiosis and fertilization • types: • gametophytic apomixis (diplospory or apospory) • adventitious embryony

  7. Apomixis in Citrus • cell in the nucellus develops into an embryo, outside the embryo sac (adventitious embryony) • nucellar embryos are clones of the maternal plant • multiple embryos are often present in 1 seed (polyembryony) • polyembryony and apomixis are unrelated, but often occur in the same seed

  8. Apomixis in Kentucky bluegrass • an embryo sac forms from a 2n cell (apospory, a form of gametophytic apomixis) • the apomictic embryo is a clone of the maternal plant • apomixis in Kentucky bluegrass is facultative

  9. Apomixis - agricultural significance • cloning virus-free Citrus rootstocks • breeding new turf types of Kentucky bluegrass: • highly sexual seed parent x highly apomictic pollen parent • select a seedling which exhibits highly apomictic seed yield and important agronomic traits • cultivars developed this way: ‘America’, ‘Eclipse’, Princeton 104’

  10. II. Cell expansion • an active period of DNA, RNA, protein synthesis • major food reserves accumulate: carbohydrates (starch), storage proteins, and lipids (oils and fats) • many food reserves are made into useful products (foods, detergents, lubricants)

  11. III. Maturation drying • physiological maturity is reached • seed (embryo) reaches max. dry weight • after this stage, seeds are either quiescent or dormant

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