Megasporangium: Definitions, Angiosperms, Functions, Types, Structure, and Megasporogenesis

Megasporangium Overview

Megasporangia are female sporangia that produce megasporocytes, which produce megaspores. Sporangia can be found in a number of structures, including fern sori, pteridophyte cones, and angiosperm blooms. Megasporangium is a sporangium that only produces megaspores. A seed plant's megasporangium, together with its surrounding integuments, is the structure in a plant that develops into a seed after fertilization. There are several gymnosperms. Microsporophylls and megasporophylls are leaf-like structures that bear microsporangia and megasporangia, respectively. 

What is Megasporangium?

Megasporangium is a plant reproductive system component. It might also be referred to as an ovule. It is made up of a nucleus and an integument. After maturity, the ovule might vary in form and size. Megasporangia are female sporangia that produce megasporocytes (mega meiocytes) that develop into megaspores. Sporangia can be borne in a variety of structures, such as sori in ferns, cones (strobile) in certain pteridophytes and the majority of gymnosperms, and flowers in angiosperms. The leaflike structures called microsporophylls and megasporophylls contain microsporangia and megasporangia, respectively. In angiosperms, these sporophylls represent the stamens and carpels of the flower; in gymnosperms, these sporophylls may be microstrobili (male cones or pollen cones) or megastrobili (pollen cones) (female cones, ovule cones, or seed cones). The presence of two spore types (microspores and megaspores) and their associated precursory structures (microsporocytes and megasporocytes; microsporangia and megasporangia; and so on), as well as subsequent structures, distinguishes the homosporous and heterosporous life histories (microgametophytes and megagametophytes).

Megasporangium in Angiosperms

Megaspores are found in the megasporangium, or ovule. Megaspores split further to form the megagametophyte. The only thing remaining after this division are fragments, which make up the entire nucellus. As a result, in an angiosperm ovule, Nucellus is the megasporangium. The nucellus is the ovule's inside. Megasporangium proper is the flower's emphasized core section, which surrounds the female gametophyte and feeds the bloom. 

Functions of Megasporangium

The following are some of the functions of the megasporangium-

1. Megasporangium (the female reproductive organ) generates megasporocytes, although, in other plants, such as Balanophora, micropylar megaspores give birth to the embryo sac.
2. One of the cells in the megasporangium divides meiotically to create the megaspores.
3. Similar circumstances occur in the Onagraceae family. 
4. The nucellus is the ovule's core component. 

Read more about the Scientific Name of Rose.

Types of Mature Megasporangium

The following are some of the types of mature megasporangiums-

1. Amphitropous: Amphitropous plants have an embryo sac shaped like a horseshoe. The most common examples are Poppy and Lemna.
2. Anatropous: Anatropous ovules are found in about 80% of angiosperms. The ovule is attached to the funicle in an inverted position.
3. Campylotropous: Campylotropous plants have an ovary that is 90 degrees to the funicle, but the micropyle is bent downward. Campylotropous ovaries are found in plants of the Leguminaceae family.
4. Hemianatropous: Hemianatropous plants have an ovule that rotates 90 degrees from the funicle. Hemianatropous ovaries are seen in Ranunculus.
5. Orthotropous: Orthotropous or atropous ovaries have the micropyle, chalaza, and funicle all on a plane. They can be found in polygonum and cycas plants. They are the simplest and least developed ovules.

Structure of Megasporangium

Megasporangia develops from the placenta, which contains ovules. An ovary can have anything from one to many ovules. Wheat, rice, and mango, for example, all have a single ovule. Ovules are abundant in watermelons, papayas, and orchids. A megasporangium, also known as an ovule, is a small structure linked to the placenta by a stalk called a funicle. The body of the ovule combines with the funicle in a region known as the hilum. The protective layer that covers an ovule is known as the integument. Except at the apex, when a tiny hole known as a micropyle is formed, integuments are composed of the nucleus. Chalaza, which represents the ovule's basal section, is located at the opposite end of the micropyle. Inside the nucellus is the female gametophyte, also known as the embryo sac. During megasporogenesis, the diploid megaspore mother cell goes through meiosis to create four haploid megaspores. Three of the four megaspores have died, leaving only one alive. The functioning megaspore gives rise to the female gametophyte. Female gametophytes have eight nuclei and seven cells, including two synergies, three antipodal cells, two polar nuclei, and one egg cell.

What is Megasporogenesis?

Megasporogenesis is the process by which haploid megaspores are formed from megaspore mother cells. To create the megaspores, the diploid megaspore mother cell splits meiotically within the megasporangium. The creation of the embryo sac is caused by the megaspore's continued mitotic division. It subsequently divides into eight haploid cells to produce the megagametophyte. It is also known as the embryo sac. When the embryo sac develops from a single megaspore, this is known as monosporic development. Two further sequential mitotic decisions occur in the creation of the embryo sac's four-nucleate and later eight-nucleate phases. Mitotic divisions are free nuclear, which means that nuclear divisions do not instantly result in cell wall construction.

Points to Remember

1. Megasporangia are female sporangia that produce megasporocytes, which produce megaspores. 
2. Sporangia can be borne in a variety of structures, such as sori in ferns, cones (strobile) in certain pteridophytes and the majority of gymnosperms, and flowers in angiosperms. 
3. The leaflike structures called microsporophylls and megasporophylls contain microsporangia and megasporangia, respectively.
4. The mother cell of a megaspore is diploid (2n), and it goes through meiosis to create four haploid (n) megaspores. 
5. The presence of two spore types (microspores and megaspores) and their associated precursory structures (microsporocytes and megasporocytes; microsporangia and megasporangia; and so on), as well as subsequent structures, distinguishes the homosporous and heterosporous life histories (microgametophytes and megagametophytes).

Conclusion

The megasporangium includes the ovules, nucellus, and integuments in flowering plants. Megasporogenesis is the process by which a megaspore divides into successive meiotic and mitotic divisions to generate a megasporangium.