Female Gametophyte

In the life cycle of all plants and some algae species, the gametophyte is a stage that can be found in the early stages of development. Both multicellular diploid generation, known as Sporophyte, and multicellular haploid generation, known as Gametophyte, are involved in this process. Sporophyte is the more complex of the two.

The term Diploid refers to cells that contain two sets of chromosomes, which are typically represented by the letters ‘2n’. Haploid refers to a cell that contains only one set of chromosomes, which is represented by the letter ‘n’.

One of the most important responsibilities of a gametophyte is the creation of Gametes. The haploid reproductive cells, such as sperm and eggs, are formed from the gametes that have been produced.

Gametophyte’s reproductive organs are

In a gametophyte, there are two types of reproductive organs that can be found:

Archegonium: 

A multicellular sex organ found in females that is responsible for egg production. It is similar to a female’s ovary in that both structures produce haploid cells for egg development.

Antheridium:

 A multicellular sex organ in the male that is responsible for the production of sperm. Because both the antheridium and the testis in human males produce haploid sperm cells, they are similar in appearance.

Both antheridia and archegonia are microscopic structures that are normally found in the human body.

Some of the gametophytes have antheridia as well as archegonia on their bodies. These are referred to as bisexual gametophytes because they include both female and male reproductive structures. A unisexual gametophyte is a gametophyte that possesses just one type of gametangium, as opposed to a bisexual gametophyte.

Haploid

A cell is said to be haploid if it only has one set of chromosomes, which is the case in most cases. In addition, the term “haploid” can refer to the number of chromosomes present in gametes, which can be either eggs in females or sperm cells in males, depending on the species.

Human gametes are haploid, which means that they contain 23 chromosomes, unlike other animals. Each of these chromosomes exists as a pair in diploid cells, and each of these chromosomes is present as a pair in diploid cells. The number of chromosomes that are present in a single set can be represented by the letter ‘n,’ where ‘n’ is also referred to as the haploid number. In the case of humans, the number is 23.

Gametes contain half of the chromosomes found in typical diploid cells of the body, whereas normal diploid cells do not. Somatic cells are the term used to describe these diploid cells.

Meiosis is the process through which haploid gametes are generated. It is a type of cell division in which the number of chromosomes in the parent diploid cell is reduced by half, resulting in a haploid cell. Some organisms, such as algae, have portions of their life cycle that are haploid in nature. Other creatures, such as male ants, continue to exist as haploid entities for the duration of their lives.

Female Gametophyte: Embryo sac

It is worth noting that the female gametophyte of gymnosperms is a large and multicellular structure that performs the dual functions of supporting gametes and nurturing the developing embryo. This is in contrast to the state of the female gametophyte in angiosperms, which is minute, typically eight-nucleated, and only contains a single functional gamete.

Female gametophytes are responsible for the generation of female gametes, as well as for the production of the molecular and physical basis for fertilisation and the initiation of the development of the seed. It is these microscopic forms that serve as the fundamental hub for plant reproduction, which is dependent on molecular processes for its development and growth. Besides gene functions, it is supported by cellular functions that are encoded by accessory cells that can become genetically active in the event of failure of one or more gametes.

Growth and Development of the Female Gametophyte

Women’s gametophyte development is divided into two distinct phases, which are described here. The first step is known as megasporogenesis, in which a single diploid mother cell undergoes meiosis to generate a haploid megaspore tetrad, of which only one will survive and the other three will dissolve, while the second phase is known as sporogenesis. The embryo sac formed by the functional megaspore is called a blastopore.

Megagametogenesis is the second phase of the life cycle, during which the functioning haploid megaspore undergoes mitosis to produce a 7-celled, 8-nucleate gametophyte known as an embryo sac. Polar nuclei are the ones that travel to the center of the cell and fuse together to form a single diploid cell at the center of the cell. This is the cell that fuses with the sperm to generate triploid endosperm, which is the product of the union. All but one of the nuclei will grow into antipodal cells, while the other two will develop into synergid cells that will eventually disintegrate.

Male Gametophyte: Pollen Grain

Microspore mother cells are transformed into pollen grains, which is the first gametophytic structure to be produced. During the germination process, which occurs prior to pollination, the pollen grain develops into a male gametophyte that reproduces.

Pollen mother cell (PMC) performs meiosis within the microsporangium, resulting in the formation of four microspores, which eventually mature into pollen grains and form pollen grains. The inner layer, known as the tapetum, provides nourishment for the developing microspores.

Pollen grains are made up of two cells: a vegetative cell and a generative cell, which are both present in the flower. Once the microsporangium has reached maturity, it bursts open, releasing the pollen from the anther into the air.

The pollen grain is made up of two layers, one on top of the other.

• The exine is the exterior thick layer, and the intine is the interior thin layer, both of which protect the pollen from being damaged by the environment.

The development of a male gametophyte can be divided into two stages: 

• Pre-pollination development and post-pollination development are two stages of development.

Growth and Development of the Male Gametophyte

A large central vacuole formation causes the nucleus to be pushed to one side, after which the nucleus undergoes mitosis, giving rise to two daughter nuclei. Precocious germination is a type of germination that occurs in the pollen sac and is characterised by the presence of a large central vacuole formation that causes the nucleus to be pushed to one side.

The small cell that forms is known as the generative cell, and the larger cell is known as the vegetative cell, which contains sufficient cytoplasm to serve as a food reserve for the development of the male gametophyte, while the generative cell forms at the mid-section of the pollen grain, and the vegetative cell is known as the reproductive cell. During this stage, the pollen grains land on the stigma, where they continue to develop further.

The pollen grains that fall on the stigma stimulate nutrition absorption through the germ pore on the stigma, which causes the vegetative cell to enlarge as a result of the pollen grains falling on the stigma. The enlargement causes the intine to travel out of the pollen tube through the germ pore, which is necessary for the creation of the pollen tube.

The pollen tube is reached by the nuclei of the vegetative and generative cells travelling together. At this stage, the generative cell divides to generate two haploids, which are the non-motile and unicellular male gametes, which are then divided again. As a result of the deeper insertion of the tube, the size of the developing male gametophyte is reduced, and the gametophyte obtains its sustenance from the tissues of the style.

Gametophytes examples

The following are some notable examples of gametophytes in action:

Mosses

The gametophyte stage of moss has a long life span, but sporophytes are long stalks that release spores when the wind blows across them. The sporophytes are generated by combining the sex cells of the gametophytes. As a result, as compared to gametophytes, they have twice the number of chromosomes present.

Hornwort

When growing on the ground, the gametophyte of hornwort is green, long-lived, and low-lying, whereas the sporophyte is a thin, long stalk from which the spores are expelled.

Hornwort gametophytes and sporophytes are two distinct organisms with differing chromosome counts, which are distinct from one another.

Conclusion

Because of genetic variation over generations, all plants reproduce both sexually and asexually.

Gametophytes and sporophytes are organisms that have genetic components from a particular plant species. Although some of the more complicated vascular plants spend longer time as sporophytes, mosses are not the same as vascular plants. The visible section of the plant is the gametophyte stage of these species, which is the most obvious component of the plant.

Haploid gametophytes have only one copy of each chromosome in each of their cells, which is why they must reproduce asexually throughout this stage of their development. Eventually, gametophytes produce gametes, which combine to form a diploid zygote, which develops into a sporophyte after maturing.

Diploid sporophytes have two copies of each chromosome, making them capable of supporting meiosis, which results in the production of haploid spores that develop into gametophytes, and so allowing for the alternation of generations.