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Learn Introductory plant breeding with Braimy- B.Sc agriculture
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  • Sexual reproduction involves fusion of male and female gametes to form a zygote, which develops in to an embryo.
  • In crop plants, male and female gametes are produced in specialized structures known as flowers.

1. Flower:

  • A flower usually consists of sepals, petals (or their modifications), stamens and/or pistil.
  • A flower containing both stamens and pistil is a perfect or hermaphrodite flower.
  • If it contains stamens, but not pistil, it is known as staminate, while a pistillate flower contains pistil, but not stamens.
  • Staminate and pistillate flowers occur on the same plant in a monoecious species, such as maize, Colocasia, castor (Ricinus communis), coconut, etc.
  • But in dioecious species, staminate and pistillate flowers occur on different plants, e.g., papaya, date palm (Phoenix dactylifera), pistachio (Pistacia vera), etc.

2. Sporogenesis:

  • Productions of microspores and megaspores is known as sporogenesis.
  • Microspores are produced in anthers (microsporogenesis), while megaspores are produced in ovules (megasporogenesis).

a) Microsporogenesis:

  • Each anther has four pollen sacs, which contain numerous pollen mother
  • cells (PMCs).
  • Each PMC undergoes meiosis to produce four haploid cells or microspores.
  • This process is known as microsporogenesis.
  • Microspores mature into pollen grains mainly by a thickening of their walls.

b) Megasporogenesis:

  • Megasporogenesis occurs in ovules, which are present inside the ovary.
  • A single cell in each ovule differentiates into a megaspore mother cell.
  • The megaspore mother cell undergoes meiosis to produce four haploid megaspores.
  • Three of the megaspores degenerates leaving one functional megaspore per ovule.
  • This completes megasporogenesis.

3. Gametogenesis:

  • The production of male and female gametes in the microspores and the megaspores, respectively, is known as gametogenesis.

a) Microgametogenesis:

  • This refers to the production of male gamete or sperm.
  • During the maturation of pollen, the microspore nucleus divides mitotically to produce a generative and a vegetative or tube nucleus.
  • The pollen is generally released in this binucleate stage.
  • When the pollen lands onto the stigma of a flower, it is known as pollination.
  • Shortly after pollination, the pollen germinates, the pollen tube enters the stigma and grows through the style.
  • The generative nucleus now undergoes a mitotic division to produce two male gametes or sperms.
  • The pollen, along with the pollen tube, is known as microgametophyte.
  • The pollen tube finally enters the ovule through a small pore, micropyle, and discharges the two sperms into the embryo sac.

b) Megagametogenesis:

  • The nucleus of a functional megaspore divides mitotically to produce four or more nuclei.
  • In most of the crop plants, megaspore nucleus undergoes three mitotic divisions to produce eight nuclei.
  • Three of these nuclei move to one pole and produce a central egg cell and two synergid cells; one synergid is situated on either side of the egg cell.
  • Another three nuclei migrate to the opposite pole to give rise to antipodal cells.
  • The two nuclei remaining in the center, the polar nuclei, fuse to form a secondary nucleus.
  • The megaspore thus develops into a mature megagametophyte or embryo sac.
  • The development of embryo sac from a megaspore is known as megagametogenesis.
  • The embryo sac generally contains one egg cell, two synergids, three antipodal cells (all haploid), and one diploid secondary nucleus.

Sporogenesis and gametogenesis in male (A) and female (B) reproductive... |  Download Scientific Diagram

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