In plants, fertilisation is the union of the male and female gametes to form a zygote. In flowering plants, double fertilisation occurs when the two male nuclei in the pollen grain fuse with the egg and the polar nuclei to form the diploid zygote and triploid endosperm.

Definition of Post-Fertilization

Post fertilisation is defined as a series of events that occur in order for the plants to produce a fruit. Following fertilisation of plants, an embryo division occurs mitotically to produce a multicellular embryo. The endosperm in a zygote breaks down to form a mass of endosperm cells, which nourish the developing embryo. 

After fertilisation, the flower undergoes a variety of transformations. The diploid zygote develops into a plant, followed by the ovary, which develops into a fruit, and the ovules, which develop into a seed.

Events of Post-Fertilization

After fertilisation, a series of events occur in the development of plants to form a fruit from a diploid zygote. The four different developmental steps that occur during post fertilisation are described below:

• The Formation of an Endosperm
• The Growth of an Embryo
• The Growth of a Seed
• Fruit Development

The Formation of an Endosperm

The development of the endosperm occurs before the development of the embryo. The essential endosperm cell divides repeatedly to form a triploid endosperm tissue.

• Most of the time, the primary endosperm nucleus undergoes progressive atomic divisions without cytokinesis to produce free atomic endosperm

• As a result, cell wall formation begins at the periphery and the endosperm becomes entirely cell, as in rice, maize, coconut, sunflower, and so on

Functions of the Endosperm

The two major goals of endosperm are listed below.

• The endosperm tissues store food materials and provide metabolic support to the developing embryo

• The endosperm is also used by the seed and aids in the development of embryos prior to seed germination

The Growth of an Embryo

The embryo development process is known as embryogeny, and it begins in the zygote at the micropylar end of the embryo sac. The zygote begins to divide after the formation of endosperm, and endosperm provides nutrition for its development. The zygote gives rise to a pro embryo, which develops into a globular, heart-shaped, mature organism. Regardless of plant structure, the stages for the formation of embryogeny are nearly identical in both dicot and monocot plants.

Embryo of a Monocot

• The monocot Embryo has only one cotyledon on one side, known as the scutellum

• The embryonal axis has a radical and root cap enclosed in an undivided coleorhiza on the lower side
• The epicotyl forms part of the embryonal axis over the scutellum like in grass, banana, bamboo, and palm, it has a shoot peak and a couple of leaf primordia encased in an empty foliar structure called a coleoptile.

Embryo Dicot

• One embryonal axis and two cotyledons make up the dicotyledonous embryo plant

• The epicotyl is the part of the embryonic axis above the cotyledon that terminates the plumule or stem tip

• The rounded part below the cotyledon level, known as the hypocotyl, terminates in the radicle or root tip
• The root tip of the hypocotyl end and the cover of the tip id are referred to as root caps in plants such as apple, mango, raddish, rose, and so on

The Growth of a Seed

In angiosperms, double fertilisation results in the development of an ovule into a seed. These seeds germinate within the fruits. The seeds are made up of three parts: the seed coat, the cotyledon, and the embryo axis.

• The integuments typically produce a double-layered seed coat
• The inner end of the integuments produces an inner layer of seed coat known as tegmen, while the outer integuments produce an outer layer of seed known as testa

• Cotyledons are usually thick and enlarged with food materials
• They are usually one to two in number and are very good at storing food

• The micropyle is a small opening found on the seed coat that allows water and oxygen into the seed

Fruit Development

Following cell division and separation in the ovary, it is transformed into fruit as a result of fertilization-induced stimuli. The ovary wall develops into the pericarp of a fruit, which can be fleshy, as in guava, tomato, and cucumber, or weathered and dry, as in pea, bean, and mustard. The pericarp protects the seeds and aids in their dispersal. Following all of the events, two types of fruits are formed:

• True Fruit: True Fruit is food that comes from the plant ovary and is associated with the non-capillary part of the plant, such as mango, tomato, and guava

• False Fruit: Fruit that grows from other accessory floral parts rather than the ovary is referred to as a false fruit and their examples include cashew nuts, strawberries, and apples

Conclusion 

In plants, fertilisation is the union of the male and female gametes to form a zygote. In flowering plants, double fertilisation occurs when the two male nuclei in the pollen grain fuse with the egg and the polar nuclei to form the diploid zygote and triploid endosperm. The endosperm in a zygote breaks down to form a mass of endosperm cells, which nourish the developing embryo. After fertilisation, the flower undergoes a variety of transformations. The diploid zygote develops into a plant, followed by the ovary, which develops into a fruit, and the ovules, which develop into a seed.