WHAT IS MEGASPOROGENESIS? - BIOLOGY - 2025

The megasporogenesis is a process of sexual reproduction in angiosperms and gymnosperms in which megasporas are formed. This process involves reductional (meiotic) cell divisions where the ovarian tissue and the stem cells of the plant give rise to embryonic sacs or also called female gametophytes.

The spore formation process is essential in the sexual reproduction of plants. The study of this and other types of embryological processes, allows to know evolutionary and taxonomic aspects of higher plants.

Development of the female gametophyte and embryo in the herbaceous plant Arabidopsis sp. Taken and edited from Double_fertilization_in_arabidopsis.jpg: * Female_gametophytic_and_early_zygotic_mutant_phenotypes_highlight_the_essential_role_of_corresponding_genes_for_reproductive_development.jpg: Johnston et al.derivative (talkativeKetative) derivative (workPC: CopperKetative)

The knowledge of the megasporogenesis process is used to understand the reproduction and achieve the genetic improvement of many plants with high commercial interest, in order to obtain successful planting cycles.

Process description

In angiosperms

Angiosperms are the group of organisms with the greatest extension and diversity among plants. They are characterized mainly by producing flowers and fruits with seeds, have a great plasticity of forms and have adapted to live almost anywhere on the planet.

From a phylogenetic point of view, this group of plants is monophyletic, which indicates that all species have a common ancestor and therefore their classification is natural.

In this group of plants, megasporogenesis begins in ovarian tissue. The mother cell of the megaspores, through two processes of meiotic division (I and II), will form four nuclei or haploid megaspores (with half the genetic load).

Of these four megaspores, the largest or highest three will degenerate or undergo cell death, while the smallest or lowest will become a functional megaspore.

The functional megaspore will give rise to the embryo sac or megagametophyte (female gamete). To form the embryo sac, three more mitotic divisions must occur, which will form eight nuclei, giving rise to the embryo sac.

In this group of plants, at least three patterns of megasporogenesis are known:

Polygonum or monosporic

This occurs in most angiosperm plants. In this process or model, a plate of cells is formed after meiotic cell division I and II, giving rise to four megaspores with a single nucleus each (uninucleated), of which three will degenerate as indicated in the previous general process, where the embryo sac is formed.

Alisma or bisporic

In this model, a cell plate is formed after meiotic cell division I, but not after meiosis II, giving rise to two binucleate megaspores (two nuclei each), in which only one undergoes cell death and the other will give rise to the sac embryonic.

Druse or tetrasporic

In this pattern, a cell plate does not form after meiotic cell divisions I and II, which gives rise to a megaspore with four nuclei (tetranucleate).

In gymnosperms

Gymnosperms are long-lived plants, capable of reaching large sizes. They are characterized by presenting very small and not very showy flowers, they do not present fruits, and their seeds are bare. Pines and firs, for example, are gymnosperm plants.

This group of plants is phylogenetically considered polyphyletic, that is, the species that make it up do not descend from the same common ancestor. So it is an unnatural group.

Megasporogenesis in this type of plants also begins, as in angiosperms, with a mother cell of the megaspores, which by meiotic cell division processes produces four haploid cells (megaspores) in a linear way.

Of the four megaspores formed, only one will be functional and will form the female gametophyte (embryo sac); said female gametophyte consists of a tissue in which 2 or 3 structures called archegonia (depending on the species), typical of some gymnosperms such as pines, have formed.

In these archegonia another mitotic division will occur to form a bulky egg cell for each archegonia. This last stage will vary between gymnosperm species. Archegonia leave openings or holes through which the male gametophyte will enter.

In these plants this process can take several months to complete, while in angiosperms, on the other hand, it can take only hours or days.

Research Applications

Taxonomy and systematics

Embryological studies focused on systematics and taxonomy, seek to resolve the phylogenetic relationships between different groups of organisms and adapt, if the case warrants it, their taxonomic classification.

In both plants and animals, such studies have helped resolve taxonomic hierarchies in higher taxa such as classes, orders, or families. Evolutionary embryology studies in plants at the species level are relatively scarce, although they have gained some strength in recent decades.

Megasporogenesis studies have been very useful in differentiating taxonomic groups throughout the world; for example, studies on ornamental plants of the Crinum, Haemanthus and Hymenocallis genera.

farming

There have been many studies carried out in embryology, especially gametogenesis of plants of commercial interest, such as rice, potatoes, corn, wheat, soybeans, among many others.

These studies made it possible to determine the ideal conditions to renew crops and to know with greater certainty the synchronization times between gametes, fertilization and development of the embryo, consequently improving the knowledge and technology applicable to the different crops.

Life cycle of an angiosperm plant. Taken and edited from: LadyofHats Mariana Ruiz. Translated by Chabacano.

Genetics

Attempts to achieve genetic improvement of plants often result in their sterility. Megasporogenesis studies and other embryological analyzes seek to reveal what happens in the reproductive process, and what is the cause for which the embryos are not viable.

For example, a study published by the FAO in 1985 showed that certain potato clones were sterile, and the analysis of microsporogenesis and megasporogenesis allowed the conclusion that the tepetum and the endothelium had lost their functional or physiological activity.

The tapetum is a tissue in charge of providing nutrients to the microspores during their development. Due to this loss of activity, the process of supplying nutrients to pollen and the female gametophyte failed. As a result of this, sterility occurred in both the female and male phases.

References

1. Magaspore. On Wikipedia. Recovered from en.wikipedia.org.
2. R. Yadegari & GN Drews (2004). Female Gametophyte Development. The plant cell.
3. Morphology of vascular plants. Unit 23, Reproduction and pollination. Recovered from biologia.edu.ar.
4. Sporogenesis. EcuRed. Recovered from ecured.cu.
5. Sexual Reproduction in Gymnosperms. Lumen. Recovered from courses.lumenlearning.com.
6. Generalities of gymnosperms. Science and Biology. Recovered from Cienciaybiologia.com.
7. MB Raymúndez, M. Escala & N. Xena (2008). Megasporogenesis and megagametogenesis in hymenocallis caribaea (l.) Herb. (amaryllidaceae) and some characteristics of its seminal development. Acta Botánica Venezuelica.
8. JS Jos & K. Bai Vijaya (1985) Sterility in a sweet potato clone. Recovered from agris.fao.org.