Pre-Fertilization: Meaning, Structures & Events

Pre-fertilization is the process that happens before real fertilization, i.e. the process that occurs before gamete fusion. Plants are capable of both sexual and asexual reproduction. Almost all blooming plants reproduce sexually. Flowers are important because they include both male and female reproductive components, known as androecium and gynoecium. Before fertilization, two events happen namely Gametogenesis, i.e, the formation of male and female gametes and Gamete transfer, which is bringing the male and female gametes together.

Key Terms: Pre-Fertilization, Pollination, Pollen Grains, Gametogenesis, Gamete Transfer, Anther, Ovule, Zygote, Flowers, Gametes

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Fertilization in Plants

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The process of amphimixis that occurs as a result of pollination and germination is known as fertilization in plants. Following carpal pollination, male gametes (pollen grains) are infused with feminine gametes (ovum) to produce a diploid zygote by a physicochemical process. The whole thing happens in a zygote, which eventually turns into a seed. 

Pollinators transport male gametes into female reproductive organs during the procedure (butterflies, honey bees, birds, flower beetles, and bats,). As a result, an embryo forms throughout the seed's growth. Angiosperm flowers are also reproductive organs, and they reproduce uniquely.

Fertilization in Plants

Read More: Morphology of Flowering Plants

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Gametogenesis

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It is the process of gamete formation. Inside the anther, male gametes are formed. Microsporogenesis and microgametogenesis are two of the phases. Megasporogenesis and megagametogenesis are the two processes involved in the formation of female gametes inside the ovules. The structures and procedures are described here.

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Structures Involved in Gametogenesis

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The structures involved in the gametogenesis process are elaborated in detail below.

• Microsporangium: The Microsporangium is surrounded by the epidermis, middle layers, endothecium, and tapetum (Pollen sac). Pollen grains are formed in this area. On the plant, there were four pollen sacs. A part of each sac is made up of sporogenous tissues, which are a collection of compactly packed homogenous tissues.
• Ovules: Ovules are the sites where female gametes develop. These are located at the bottom of a carpel, which is a vase-like structure with a style neck and a stigma opening at the top.
• Pollen Grains: Pollen Grains are available in a range of sizes. It has two walls: a cellulose-based inner wall called endospore and a sporopollenin-based outer wall.
• Anther: The anther is a two-lobed structure. The strip of the sterile section is connected to the two lobes.
• Stamen: The stamen's filament is the stalk. The thalamus, which is a flower petal, is linked to the filament's proximal end.

Structure of Flower in Sexual Reproduction

Read More: Flower Structure

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Formation of Male Gametes

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The process of formation of Male Gametes is as follows: 

Microsporogenesis

• Microsporogenesis is the first step in the production of microspores or pollen grains in the microsporangium, the pollen sac of the anther.
• Meiosis produces four haploid microspores from the diploid pollen mother cell.
• A pollen grain develops from each microspore.

Read More: Difference between Haploid and Diploid

Microgametogenesis

• The creation of a male gametophyte from a pollen grain is known as micro gametogenesis.
• Pollen grains undergo mitosis, which produces two types of cells: smaller reproductive cells and larger vegetative cells. Pollination takes happens in this area.
• The generative cells create two male gametes, whilst the vegetative cells produce pollen tubes.

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Formation of Female Gametes

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The process of formation of Female Gametes is as follows: 

Megasporogenesis

• The megaspore forms in the megasporangium. This process is known as megasporogenesis.
• The process takes place in the nucellus, a structure within the ovule.
• The diploid megasporocyte within the ovule undergoes meiosis, culminating in the creation of four haploid megaspores.
• Only one megaspore grows into a megagametophyte, while the other three dissolve.

Mega-gametogenesis

• The female gamete is produced by a fully functional megaspore. This process is known as megagametogenesis.
• The megaspore undergoes three rounds of mitosis before forming an embryo sac with eight nuclei.
• Each chalaza, micropyle, and the end had four nuclei at first. During fertilization, one of them from each pole merges in the centre to form a diploid nucleus.
• The three cells eventually dissolve at the chalaza end chalaza.
• The egg cell develops from one of the three cells at the micropyle. The last two secrete chemicals that guide the pollen tube.

Read More: Difference Between Pollination and Fertilization

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Gamete Transfer

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Pollination is the transfer of pollen grains from one strong bloom to the stigma of another, and it is the same as reproduction. It's also possible that it'll show up in the same blossom. This method is the initial step in sexual reproduction in flowering plants. Pollen grains contain the male gamete, which is located in the anthers of the floral part.

Pollination

Read More: Difference Between Cross-Pollination and Self Pollination

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Things to Remember

• Pre-fertilisation can be defined as the process that occurs before the fusion of gametes or actual fertilization. 
• Two events take place before fertilization namely Gametogenesis (Formation of male and female gametes) and Gamete transfer (Bringing the male and female gametes together).
• Gametogenesis is the process of formation of male and female gametes. 
• The male gametes are formed inside the anther and involve two major steps namely microsporogenesis and microgametogenesis in their formation. 
• Similarly, the female gametes are formed inside the ovules and involve two steps namely megasporogenesis and megagametogenesis. 
• Pollination is essential for the formation of seeds. In pollination, the pollen grains are transferred to the stigma from anther. They germinate on the stigma and reach the ovule through the pollen tube, where the male gametes are then released near the egg.