What Happens Before Fertilisation: An Introduction
Plants can reproduce asexually and sexually. All blooming plants almost always reproduce sexually. Flowers are significant because they contain the androecium and gynoecium, or male and female reproductive organs. Gametogenesis, or the development of the male and female gametes, and gamete transfer, or the joining of the male and female gametes, take place prior to fertilisation. Keep reading ahead to learn more about pre fertilisation events.
What is Pre-Fertilisation?
Pre-fertilisation is the procedure carried out prior to actual fertilisation or the procedure carried out before gamete fusion.
Plant Pre Fertilisation
In plants, fertilisation is the amphimixis that happens due to pollination and germination. After carpal pollination, male gametes (pollen grains) are combined with female gametes (ovum) by a physicochemical process to create a diploid zygote. A zygote, which finally develops into a seed, is where the entire process takes place.
During the process, pollinators transfer male gametes into female reproductive organs (butterflies, honey bees, birds, flower beetles, and bats). As a result, during the seed's development, an embryo develops. The reproductive organs of angiosperm flowers are distinct from other reproductive organs.
Gamete Formation
Gametogenesis is the gamete creation process. The male gametes are created inside the anther. Two of the phases are microsporogenesis and microgametogenesis. The two processes contributing to the development of female gametes inside the ovules are megasporogenesis and megagametogenesis. Here are descriptions of the structures and processes.
Pre Fertilisation Structure
Microsporangium: The endothecium, tapetum, middle layers, and epidermis surround the microsporangium (Pollen sac). In this region, pollen grains are created. There were four pollen sacs on the plant. The sporogenous tissues, a group of tightly packed homogeneous tissues, comprise a portion of each sac.
Ovules: The locations where female gametes develop are called ovules. These are found near the base of a carpel, which is shaped like a vase and has an aperture for the stigma at the top.
Pollen Grains: A variety of sizes are offered for pollen grains. It has an outer wall made of sporopollenin and a cellulose-based inner wall known as an endospore.
Anther: A two-lobed structure is an anther. The two lobes are joined by the strip of the sterile portion.
Stamen: The filament of the stamen is its stalk. The proximal end of the filament is connected to the thalamus, which resembles a flower petal.
Pre-Fertilisation Events
The pre-fertilisation events are as follows:
Male Gametes Formation
The following is the method of pre fertilisation structure and events by which male gametes are formed:
Microsporogenesis: The initial stage of microsporogenesis occurs in the microsporangium, the pollen sac of the anther, where microspores of pollen grains are produced. The diploid pollen mother cell undergoes meiosis to produce four haploid microspores. Each microspore grows into a pollen grain.
Microgametogenesis: Micro gametogenesis is the process through which a pollen grain develops into a male gametophyte. Mitosis, a cell division process, divides pollen grains into two types of cells: smaller reproductive cells and bigger vegetative cells. In this area, pollination occurs. While the vegetative cells form pollen tubes, the generative cells produce two male gametes.
Female Gametes Formation
The following is the method by which female gametes are formed:
Megasporogenesis: In the megasporangium, the megaspore forms. Megasporogenesis is the name of this process. The nucellus, a part of the ovule, is where the process takes place. The ovule's diploid megasporocyte goes through meiosis, producing four haploid megaspores. The other three megaspores disintegrate, while only one develops into a megagametophyte.
Mega-gametogenesis: A functional megaspore produces the female gamete. Megagametogenesis is the name for this process. Megaspores go through three cycles of mitosis before developing an eight-nucleate embryo sac. At first, each chalaza, micropyle, and the end had four nuclei. A diploid nucleus is formed when one of them from each pole unites in the centre during fertilisation.
At the chalaza end of the chalaza, the three cells gradually disintegrate. One of the three cells at the micropyle gives rise to the egg cell. The final two release substances that direct the pollen tube.
Transfer of Gametes
Pollination, which is the same as reproduction, is the movement of pollen grains from one robust bloom to the stigma of another. Additionally, it's possible that it will appear in the same flower. The first stage of sexual reproduction in flowering plants begins with this technique. The male gamete, found in the floral part's anthers, is present in pollen grains.
Interesting Facts
Spermatogenesis and oogenesis are the processes by which male and female gametes are created. The development of ova is aided by oogenesis, whereas the development of sperm is aided by spermatogenesis. A zygote is created when sperm and ova combine, and this zygote later grows into an embryo.
The primary endosperm cell is created when the other sperm nucleus fuses with the binucleate central cell, while the zygote is created when one sperm nucleus fertilises the egg cell. From the cell formed during multiple fertilisation, the endosperm grows.
A single fertilised egg can create two or more embryos, leading to identical twins in humans in a condition known as polyembryony. A common occurrence in many plant and animal species is polyembryony. The nine-banded armadillo, which typically bears four identical young, exhibits it.
Important Questions
Define Pollination.
Ans: Pollen transfer refers to the movement of pollen from an anther to a stigma in angiosperms or from a microsporangium to a micropyle in gymnosperms.
Who identified pollination?
Ans: Christian Konrad Sprengel.
Key Features
The two main processes, microsporogenesis and microgametogenesis are used to generate the male gametes inside the anther.
Similar to how male gametes develop inside ovules, female gametes also go through two stages of development: megasporogenesis and megagametogenesis.
For seeds to develop, pollination is necessary. The male gametes are subsequently released close to the egg after they germinate on the stigma and travel to the ovule through the pollen tube.
FAQs on Pre-Fertilisation
1. What happens in flowers to cause fertilisation?
When pollen grains land on the stigma, a pollen tube stretches from the grain, through the style, and into the ovary. Sperm cells from the pollen grain enter the ovary, which contains the ovules, through the pollen tube. The process of fertilisation starts when one sperm cell joins an egg inside an ovule.
2. What is double fertilisation?
Only flowering plants go through the unique process of two-fold fertilisation. After entering the synergid, one of the male gametes joins the nucleus of an egg cell to create the zygote. The primary endosperm nuclei are produced when a second male gamete interacts with the polar nuclei. This procedure is called double fertilisation since it necessitates triple fusion and syngamy.
3. What does the endosperm do?
The endosperm is critical in encouraging embryonic growth throughout seed development and germination by supplying nutrients, shielding the embryo, and controlling embryo expansion by acting as a mechanical barrier.
