Monosporic: The formation of the female gametophyte from a single functional megaspore is called as monosporic development. The nucleus of functional megaspore divides mitotically to form two nuclei which move to opposite poles. This forms a two-nucleate embryo sac. Two more sequential mitotic nuclear divisions result in the formation of four-nucleate and eight-nucleate stages of embryo sac.

These mitotic divisions are free nuclear type in which karyokinesis is not followed immediately by cytokinesis. After the eight-nucleate stage, the walls are laid down leading to the organization of the typical female gametophyte. Six of eight nuclei are surrounded by cell walls and organized into cells; the remaining two nuclei, called polar nuclei are situated below the egg apparatus in the large central cell. A typical angiosperm embryo sac at maturity is eight nucleate and seven cells. Three cells lie at micropylar end forming egg apparatus. Three ends at chalazal end called as antipodal cells. A single large central cell which has two polar nuclei.

Monosporic Embryo Sac

• Embryo sac refers to the female gametophyte in an angiosperm.
• The embryo sac is found within the nucellus and integuments of the ovule or the megasporangium.
• In most angiosperms, a single megaspore produces a female gametophyte.
• Megasporogenesis is the process of the formation of megaspores.
• The diploid megaspore mother cell divides into four megaspores during meiosis.
• Only one functioning cell contributes to the development of the embryo sac after the degeneration of three cells and this type of embryo sac is known as a monosporic embryo sac.
• This type of embryo sac development is known as monosporic development.

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By Team Learning Mantras