Index

• Overview
• Process
• Variants of Embryo Sac Formation

Overview

Megasporogenesis is the process that leads to the formation of megaspores from the megaspore mother cells. These megaspores are developed within the female reproductive organs of a plant.

Process

• Within the ovules of a female plant, there exists a layer of sporogenous tissue.
• The megaspore mother cells (MMC) are formed from this sporogenous tissue. MMC is a large diploid cell that houses a prominent nucleus and dense cytoplasm.
• The MMC undergoes meiotic nuclear divisions to produce four haploid megaspores.
• These megaspores are arranged in a linear fashion, forming a linear tetrad.
• Out of these four, only one megaspore is functional while the other three degenerate.
• The functional megaspore is located at the chalazal end, and the three degenerate ones are towards the micropyle.
• This functional megaspore divides mitotically to form the embryo sac, a process known as megagametogenesis.
• The functional megaspore undergoes multiple divisions to produce eight haploid nuclei for the embryo sac, which is also referred to as a megagametophyte.

Read: Formation of Embryo Sac

Variants of Embryo Sac Formation

1. Monosporic

In most angiosperms, the embryo sac develops from one functional megaspore while the other three degenerate. For example, in plants like Alisma, Ranunculus.

2. Bisporic

Here, two of the megaspores participate in the formation of the embryo sac. Examples include plants like Plumbago, Primula , and Lilium .

3. Tetrasporic

In this case, all four megaspores contribute to the formation of the embryo sac. For instance, in plants like Brassica.

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Also, see:

• Comparison: Megasporogenesis vs Microsporogenesis
• Diagram of Mature Embryo Sac