Post Fertilisation - Events in Flowering Plants: Structures And Events

Definition Of Fertilisation

In flowering plants, fertilisation is the process by which a male and a female gamete are combined in an ovule to form a zygote. Such a fundamentally overwhelming process is triggered by the transfer of pollen to the stigma and then by the growth of the pollen tube, which allows access of the sperm cells to the egg cell for fertilisation in the embryo sac.

Equally important are the following processes after fertilisation, as they start the development of seeds and fruits. This includes division and later differentiation of the zygote into an embryo, followed by the formation of endosperm for nourishment and the process through which the ovule matures into a seed and the ovary matures into a fruit, thereby ascertaining propagation and survival of plant species.

Formation Of The Zygote

One of the sperm cells, from a pollen grain, fertilises an egg cell in the ovule to form a zygote.

Definition And Formation

The fusion of the male to the female gamete becomes the key event in giving rise to a new organism of a plant; this marks the initiation of seed development.

Structure And Development

After fertilisation, the zygote directly undergoes several mitotic cell divisions to form a multicellular structure, the embryo. The latter will differentiate to produce all the tissues and organs of the mature plant.

Endosperm Development

The endosperm development is explained-

Types Of Endosperm

The endosperm may develop in one of the following ways:

• Nuclear endosperm: It is characterised by free nuclear divisions without immediate cell wall formation.

• Cellular endosperm: In this type, the cell wall forms immediately after each nuclear division.

• Helobial endosperm: It is intermediate between the free nuclear and cellular endosperm. In this, the primary division results in one large cell and one small cell.

Process Of Endosperm Development

Soon after fertilisation, the endosperm develops and grows to form a store of nutrition that feeds the growing embryo. The endosperm undergoes successive cell divisions and differentiates to achieve its job.

Functions Of Endosperm

The endosperm supplies the embryo with the required nutrients in the form of starch, proteins, and oils for its growth and development till the seedling becomes photosynthetic.

Embryo Development

The Stages of embryogenesis are:

Embryogenesis consists of just a few differentiated steps. These are:

• Globular stage: It is when the embryo is a spherical mass of cells.

• Heart-shaped stage: The differentiation of the embryo starts and it begins to form the rudiments of cotyledons or the seed leaves.

• Torpedo stage: Further differentiation occurs in the embryo to elongate it and form the fundamental structure of the plant.

Monocot Vs. Dicot Embryo Development

The more primitive, lower monocot embryos develop a single cotyledon whereas

Higher dicot embryos develop two cotyledons. This difference affects the overall structure of the seed and the initial pattern of growth.

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