Post Fertilization - Events And Changes In Flowering Plants

Fertilization In Flowering Plants

Fertilization in flowering plants is the process by which male and female gametes fuse to form a zygote.

Description Of Fertilization Process

The fertilization process is described below:

Pollination

• Self-pollination: This is the transfer of pollen from anther to the stigma of the same flower, or different flower of the same plant.

• Cross-pollination: This is the transfer of pollen from the anther of one plant to another plant's stigma.

Double Fertilization

• A pollen grain lands on the stigma, germinates and produces a pollen tube.

• The pollen tube grows down the style and into the ovary to the ovule.

• One sperm combines with an egg cell to form a zygote (2n).

• The other sperm combines with two polar nuclei to form the triploid endosperm (3n).

Post-Fertilization Changes

• Such post-fertilization changes in a flower are necessary for the formation of seed and fruit.

• This is a continuous process that finally propagates to the perpetuation of the plant life cycle.

Development Of Zygote

• Mitotic division of the zygote forms the embryo.

Endosperm Development

• The triploid cell divides to nourish the developing embryo.

Seed Development

The sequence from the development of the zygote to the embryo brings about seed formation.

Zygote To Embryo Stages

The stages are described below:

Proembryo Stage

• Initial divisions of the zygote.

Globular Stage

• The embryo becomes spherical.

Heart Stage

• The embryo becomes heart-shaped as cotyledons develop.

Torpedo Stage

• Additional elongation and differentiation of the embryo.

Development Of Seed Coat

The zygote's developmental series goes through a couple of stages of development that eventually lead up to seed formation.

Zygote To Embryo Development Stages

The development stages are given below:

Proembryo Stage

• Initial cell divisions of the zygote.

Globular Stage

• The embryo develops into a sphere.

Heart Stage

• The embryo takes on a heart-like shape as cotyledons develop.

Torpedo Stage

• Further elongation and differentiation of the embryo.

Seed Coat Formation

• The protective outer layers develop from the integuments of the ovule.

Maturation Of Seed

• The accumulation of nutrients.

• Seeds become dehydrated and their coats harden.

Endosperm Formation

The endosperm develops after fertilization and serves to nourish the embryo.

Endosperm Type

• Nuclear: Free nuclear divisions followed by cell wall formation.

• Cellular: Cell wall formation coincides with nuclear divisions.

• Helobial: A fusion of nuclear and cellular types.

Role Of The Endosperm In Seed Development

Supplies nutrition to the developing embryo.

Development Of The Fruit

The ovary becomes a fruit, which serves to protect and disperse the seed.

Transformation Of The Ovary Into Fruit

• The ovary wall thickens and differentiates into pericarp layers.

Types Of Fruits

• Simple Fruits: Derived from a single ovary (e.g. cherry).

• Aggregate Fruits: Originate from several ovaries of one flower (e.g. raspberry).

• Multiple Fruits: Originate from ovaries of several flowers (e.g. pineapple).

Hormones And Fruit Development

• Auxins: Stimulate cell elongation.

• Gibberellins: Promote growth and development.

• Cytokinins: Stimulate cell division.

Methods Of Seed Dispersal

Seed dispersal mechanisms contribute to the distribution of seeds for species propagation.

• Wind: Seeds are light enough to become airborne (e.g. dandelion).

• Water: Seeds are buoyant and distributed by water (e.g. coconut).

• Animals: Seeds have either barbs or an attached nutritious reward to attract animals that disperse them (e.g. burs, berries).

• Mechanical: Explosive release, for example, touch-me-not.

Seed Adaptations For Various Means Of Dispersal

• Special structures such as wings or flotation organs.

Role Of Seed Dispersal In Plant Reproduction

• Spreads plants out, reduces competition, and enhances colonization of new locations.

Seed Dormancy And Germination

• Dormancy provides for seed survival during adverse conditions until the seed germinates.

• A resting or quiescent state of metabolic inactivity.

Factors That Affect Dormancy

• Temperature: Low temperatures can initiate dormancy.

• Moisture: Amount of available water impact.

• Light: Some seeds require the action of particular light intensity to end dormancy.

Process Of Seed Germination

• Imbibition: Water uptake by the seed.

• Activation of Enzymes: Stored nutrients are hydrolysed by enzymes.

• Radicle and Plumule Emergence: Root and shoot development.

Favourable Conditions For Germination

• Correct Temperature, water, oxygen, and light.

• Environment plays an essential role in determining changes after fertilisation and the process of seed development.

• Action of Temperature, Water, Light, and Soil on Changes after Fertilisation

• Appropriate environmental conditions are required for the development of seeds and fruits.

• Effects of Biotic Factors, for example, Pests, Pollinators

• Biotic interactions can affect fertilization, seed development as well as dispersal.

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