Fertilisation in Plants: Introduction, Structures, Methods

If you are excited to learn about fertilisation in plants, you have come to the right place!

Female Hormones

Introduction

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Fertilisation in Plants

Pre-Fertilization Events

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Gametogenesis

Structures

• Epidermis, endothecium, middle layers, and tapetum make up its four walls, forming the microsporangium (pollen sac) which creates the pollen grains. The pollen sacs are four in number. A collection of tightly packed homogeneous tissues called sporogenous tissues make up the centre of each sac.
• Ovules: The location where female gametes are formed. They are located at the base of a vase-like structure called a carpel, which also contains an aperture at the top called the stigma and a neck called the style.
• Pollen grains come in a range of sizes. They have two walls: an inner wall known as an endospore, made of cellulose, and an exterior wall made of sporopollenin.
• The structure of the anther has two lobes. The strip of the sterile section is joined to the two lobes.
• The filament is a stalk that makes up the stamen. The filament's proximal end is joined to the thalamus, a flower petal.
• creation of male gametes

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Microsporogenesis

• In the pollen sac of an anther known as a microsporangium, microspores or pollen grains first develop through microsporogenesis.
• Using meiosis, the diploid pollen mother cell produces four haploid microspores.
• Each microspore matures into a pollen grain.

Microgametogensis

• Microgametogenesis is the process through which male gametophytes develop from pollen grains.
• A pollen grain goes through mitosis and divides into two types of cells: small generative cells and large vegetative cells. This is where pollination happens.
• While the vegetative cells give rise to the pollen tube, the generative cells produce two male gametes.

Megasporogenesis of Female Gametes:

• Within the megasporangium, the megaspore grows through megasporogenesis.
• The process happens inside the nucellus, a component in the ovule.
• The ovule's diploid megasporocyte goes through meiosis to split into four haploid megaspores.
• While the other three megaspores disintegrate, only one matures into a megagametophyte.

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Megagametogenesis

• The functioning megaspore produces the female gamete through megagametogenesis.
• The megaspore goes through three rounds of mitosis and produces an embryo sac with eight nuclei.
• At first, there are 4 nuclei in each micropyle and chalaza end. One from each pole fuses at the centre during fertilisation to form a diploid nucleus.
• Later, the three cells at the chalaza end disintegrate.

Pollination

Pollination Methods

• Autogamy or self-pollination and
• Allogamy or cross-pollination.

• Pollination brings blooming plants' non-motile male and female gametes closer together so that syngamy or fertilisation can occur.
• Cross-pollination introduces novel gene combinations, which aid species development.

Pollen Germination

• Pollen starts germinating if the stigma is receptive and touches a compatible species.
• A brief cytoplasmic extension known as a germ tube, which developed during the degeneration of a pollen tube, emerges from the germ pore carrying the intine (the interior integument of a pollen grain) and its contents.
• Calcium-boron-inositol sugar complex molecules responsible for the pollen tube's direction towards the ovary cause it to be positively chemotropic and negatively aerotropic. (grows away from the air).
• The pollen tube's development is stimulated and nourished by the sucrose solution released by the stigma's epidermal cells.
• To pass through the stigma, style tissues, and reach the ovule, the pollen tube generates certain enzymes.
• The vegetative or tube nucleus and the generative nucleus are the two nuclei that make up the pollen tube.
• The pollen tube's tube nucleus, located at the tip, directs the pollen tube's development until it eventually disintegrates.
• Male gametes are two male nuclei created when the generative nucleus splits via mitosis.
• Through a tiny aperture known as the micropyle, the pollen tube develops and penetrates the ovule.
• The filiform mechanism, which directs the pollen tube's entrance, allows the pollen tube to enter one of the synergids.

Double Fertilisation

• One of the synergids breaks down after getting inside the embryo sac.
• The synergids' cytoplasm is where the two male gametes are released from the pollen tube.
• Primary fertilisation: The diploid zygote is created when the egg nucleus and one of the male gametes (n) fusion together (2n). It's also referred to as syngamy, and it's the first fertilisation process.
• Second fertilisation: In the centre cell, the other male gamete relocates and fuses with the secondary diploid nucleus or the two polar nuclei, (formed by the fusion of 2 polar nuclei). The primary endosperm nucleus, a triploid nucleus, is created by this fusion. The second fertilisation process or triple fusion is used to describe this procedure.

Post-Fertilization Events

• The seed embryo is created by mitotic division of the diploid zygote (2n).
• The primary endosperm nucleus (PEN), also known as the triploid nucleus (3n), develops into a mass of tissue that becomes the seed's endosperm. The developing embryo receives nutrition from the endosperm.
• The stigma, style, and petals wilt and typically fall off.
• If the calyx is intact, it will either fall off or take on the dry, shrivelled appearance of a tomato, guava, etc.
• The fruit wall is part of the ovary wall as it enlarges to become the fruit. A soft fruit wall or a dry, hard fruit wall can develop from the ovary wall.
• Ovules form seeds.

Fertilisation Significance

• Have you ever considered how a flower converts into a fruit? How are the seeds of a plant formed?
• The answer to the above questions is ‘Double Fertilization’ because seeds and fruit result from double fertilisation. Without this unique fertilisation, a plant can not have fruits and seeds.
• Once the double fertilisation is completed- the zygote and the PEN are formed. Further, during post-fertilization events, the zygote is developed into the embryo.
• The PEN is converted into the endosperm that will nourish the developing embryo; without an endosperm, the embryo cannot develop. Have you ever wondered why coconut water is considered among the healthiest drink?
• All credit goes to the endosperm because the water inside the green coconut is nothing but its endosperm which is highly rich in minerals, ions, and nutrients.
• During post-fertilization events, the flower's ovary converts into the fruit, the ovule converts into the seed, and this seed has its embryo inside it to help germinate it.

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