What is Fertilization?
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 -
Endosperm
Embryogeny
Seed
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 -
Nuclear formation
Successive nuclear divisions occur to the primary endosperm nucleus and create a wall free nuclear endosperm.
Cellular formation
Subsequently, from the periphery, the creation of a cell wall also starts, and cellular endosperm occurs. Example: rice, coconut, maize, etc.
Helobial formation
In between nuclear and cellular endosperm formation, another intermediate endosperm formation happens, and that is known as helobial formation.
Objective of Endosperm
Endosperm tissue cells reserve starch as food and provide metabolic support to the embryo.
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
Seed Coat
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.
Cotyledon
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.
Embryo Axis
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
True 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.
False Fruit
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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FAQs on Post Fertilization Events in Plants
1. Mention the Importance of Post Fertilization Changes in Flower
Through the post-fertilization changes, a zygote transforms into a seed, and the concerned plant species continues its existence. The flowers main function was the fertilization process and after it has been done, the flower is dismantled and the various parts of the plants are reused or functioned for the post-fertilization phase of the reproduction, like the ovule of the flower transformed into the seeds and the ovaries, converts for the formation of fruits.
2. What is Post-Fertilization?
Post-fertilization is a process of successive events that occurs in the zygote and helps it become a seed. After the successful fertilization event in a plant, all the next series of functions related to the reproduction cycle can be considered as the Post - fertilization events. The four most important events that occur in this cycle of plant reproduction are
Formation of the Endosperm from PEC (primary endosperm cell)
Development of the embryo from the Zygote.
Transformation of the Ovule into the seeds.
Transformation of the ovaries into the fruits.
3. What Takes Place After Fertilization?
After fertilization, the zygote forms, and post-fertilization events happen in it. The zygote then develops to form the embryo or the embryonic plant and to successfully send it, to find a nice piece of soil and grow in there, the plant also produces endosperms. To protect these embryonic plants, the plant encloses it in seed, sometimes the seed is also covered in the fruits, which are also formed after the fertilization from the ovaries. When the development cycle of the embryonic plant, endosperm, seeds, and fruits are ready, then the embryonic plants will be dispatched from the plant to grow and continue the cycle.
4. What are the seeds and what are the Advantages of seeds?
The formation of the seeds in a plant is the post-fertilization part of the reproduction cycle of many types of plants. Seeds enclosed a plant, which is in its embryonic stage, inside it. Seeds are the product of ripened ovules, after fertilization by the pollen grains. The spermatophytes, including the gymnosperm and angiosperm plants, use the formation of the seeds as a means to reproduce because the seeds provide many benefits to the plant.
Some of the advantages the seed-producing plants get over the plants who don’t produce seeds are -
Seeds provide a protective coat for the embryo plant, so it can remain safe till it finds nice soil. Also to easily develop on a nice piece of soil, the embryonic plant will seek protection provided by the protective coats of the seed.
Food reserves come well packed in the seeds, so that needs of the plants in their early stages can be fulfilled.
Seeds are easy to disperse by animals, wind, and by birds too, which help the plant species to conquer a great piece of land. Some plant species create their seeds in such a manner that they can get eaten by animals and they spread them to the various parts of the forest.
5. What are the Functions of the endosperms in the plant's reproduction cycle?
Endosperms are tissues that are present in the seeds of the plant and perform many important functions there for the proper germination of the seed and the continuation of the reproduction cycle. Some of the most important functions performed by the endosperms in the plant seeds are given below:-
The endosperms provide protection to the developing embryo plant and also supply nutrients.
It also carries all the necessary food required for the healthy development of the embryonic plant.
Endosperms are the one who looks for the best environmental conditions for the germination of the seed.
They have the ability to control the speed of germination, seed growth and can even regulate the gene expressions.
