Fertilization is the fundamental step to initiate the reproductive system in plants. In this process, the female and the male gamete merge to produce a diploid zygote. A series of post-fertilization events take place in the zygote, and a seed develops.
Angiosperm is the most developed species of plant that consists of flowers, stems, leaves, and roots. Flower acts as a carrier of seeds. The formation of the seed occurs in the ovule a fruit develops, inside an ovary that forms in flowers.
In the reproductive system of a plant, after fertilization, several changes happen that cause the development of a fruit. Here are the four developmental steps to describe the post-fertilization changes in a flower –
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Endosperm
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Embryogeny
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Seed
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Fruit
Development of Endosperm
The endosperm, a tissue, present in the seed during the fertilization, precedes the development of an embryo. The development of endosperm can be categorised into three types –
Successive nuclear divisions occur to the primary endosperm nucleus and create a wall free nuclear endosperm.
Subsequently, from the periphery, the creation of a cell wall also starts, and cellular endosperm occurs. Example: rice, coconut, maize, etc.
In between nuclear and cellular endosperm formation, another intermediate endosperm formation happens, and that is known as helobial formation.
Objective of Endosperm
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Endosperm tissue cells reserve starch as food and provide metabolic support to the embryo.
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The endosperm also mechanically supports the embryo and helps in its development. Contrastingly, during seed germination, the endosperm is utilised by the seed.
Development of Embryo
The development process of an embryo from the zygote is known as embryogeny. This is the second post fertilization event. Mostly, after some endosperm formation, the zygote starts dividing. At first, the zygote develops to a pre-embryo and then it matures to a complete embryo.
The stages of embryogeny are similar for dicot and monocot plants. However, they have different structures.
Dicot Embryo
The embryo in a dicot plant has one embryonal axis and two cotyledons. The part of the embryonal axis above the cotyledon level is called epicotyl and hypocotyl, which is situated below the cotyledon level. The hypocotyls end in the root tip and the cover of the tip is known as root cap.
Monocot Embryo
Monocot plants have one cotyledon, called scutellum. Coleorhiza, an undifferentiated sheath, covers the root cap. Above the scutellum, the part of the embryonal axis is known as epicotyl. A shoot apex and some leaf primordia called coleoptiles are present in epicotyl.
Development of Seed
Usually, a Seed has Three Body Parts
The seed coat is double-layered and made by integuments. Testa is the hard outer part of the seed coat. Tegmen is the inner part of the seed coat. A small opening on the seed coat, called micropyle, helps in water and oxygen movement in the seed.
There are one or two cotyledons present in a seed. These cotyledons are swollen and thick due to the preservation of foods for the seed.
The embryonic root and shoot are together called the embryo axis. The part of this axis above cotyledon grows as a shoot, and the lower part becomes the root.
Various Types of Seeds
There are mainly two types of seeds in existence in the plant kingdom, these are – Monocotyledonous Seed and Dicotyledonous Seed.
Monocotyledonous Seed: as the name suggests, these are the seeds with only one cotyledon. Seeds of cereals are its examples
Dicotyledonous Seed: they have two cotyledons. Castor seeds are its example
Development of Fruit
A fruit develops through differentiation and cell division process in the ovary. The ovary wall matures into pericarp (which is the fruit wall). In some fruits like guava, cucumber, etc. the pericarp is fleshy. However, in pea, mustard, etc. a leathery pericarp is found.
The primary function of the pericarp is to protect the seed from any damage. It also helps the seed to disperse.
Types of Fruit
Without the association of the non-capillary part, when a fruit derives from the ovary of a flower, it is called true fruit.
Example: Mango, Guava, Tomato, etc.
Other than an ovary, when a fruit derives with the help of other accessory parts of a flower, it is called false fruit.
Example: Strawberry, Cashew Nut, etc.
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