Post-fertilization Definition Structures and Events

Post-fertilization Events

Development of endosperm, embryo, maturation of ovule into seed and ovary into fruit are collectively termed as post-fertilization events.

(toc)

The following events after double fertilization are collectively called post-fertilization events: 

• (i) Development of endosperm from primary endosperm nucleus (PEN) 
• (ii) Development of embryo from zygote 
• (iii) Development of seeds from ovule 
• (iv) Development of fruit from ovary

Endosperm

• It is a mass of nutritive cell produced as a result of triple fusion through mitotic division.

• On the basis of development, it is of three types.

1. In nuclear type, which is a common method, the Primary Endosperm Nucleus (PEN) undergoes repeated mitotic division without cytokinesis. At this stage, the endosperm is called free- nuclear endosperm.
2. In cellular type, cell wall formation occurs, and the endosperm becomes cellular. The number of free nuclei formed before cellularization varies greatly, e.g., in coconut the water is free nuclear endosperm and surrounding white kernel is cellular endosperm.
3. In halobios type endosperm formation, one half of endosperm is nuclear type and other half is cellular type.

Functions 

• (i) The cells of endosperm tissue are triploid and filled with reserve food material to nourish the developing embryo. 
• (ii) The water of tender coconut in the Centre is free-nuclear endosperm and white kernel in the outer part is the multicellular endosperm. 
• (iii) The endosperm may be completely consumed by the developing embryo, e.g., pea, beans, or it may persist in mature seed, e.g., coconut.

Embryo

• It develops at the micropylar end of the embryo sac where the zygote is situated.

• Embryo formation occurs when certain amount of endosperm is formed, because endosperm provides nutrition for embryo development. 

1. Zygote divides by mitosis and forms proembryo.
2. This results in the formation of globular and heart-shaped embryo that finally becomes horseshoe-shaped (mature embryo) having cotyledon.

• Dicot embryo consists of two cotyledons and an embryonal axis between them...

1. The part of embryonal axis above the level of cotyledons is the epicotyl which becomes plumule (shoot).
2. The part of embryonal axis below the level of cotyledons is the hypocotyl which becomes radicle or root tip.

• Monocot embryo consists of only one cotyledon (called scutellum in grass family), e.g., rice, maize plants, etc.

1. Embryonal axis has the radicle on its lower end (hypocotyl), the radicle is covered by an undifferentiated sheath called coleorhiza.
2. At the upper end (epicotyl), the embryonal axis has plumule. It is covered by a hollow foliar sheath called coleoptile. 

Evolutionary Significance of Trochophore Larva, Introduction, Structure, Metamorphosis, Development, Significance, Affinities Torsion and Detorsion in Gastropodal, Introduction, Definition, Mechanism of Torsion, Effect of Torsion, Significance of Torsion, Detorsion What is Mollusca? write its Characteristics and Classification with examples What is Respiration in Mollusca? writes its types of Respiration. Structure and Function of Heart Water Vascular System in Asteroidea, Introduction, Water Vascular System, Working Mechanism, Function +3 Botany Honors Paper in CBCS Syllabus Model Notes +3 Zoology Honors Paper in CBCS Syllabus Model Notes Asexual Reproduction Definition , Classification with Examples Sexual Reproduction Definition, Characteristics Gametogenesis Definition, Characteristics and Types Structure and Function of Flower Male Reproductive Unit of Flower or Stamen

Structure of dicotyledonous embryo 

•  (i) A typical dicotyledonous embryo consists of an embryonal axis and two cotyledons. 
• (ii) The portion of embryonal axis above the level of cotyledon is called epicotyl, which develops into plumule or baby shoot (future shoot). 
• (iii) The cylindrical portion below the level of cotyledon is the hypocotyl, which develops into radicle or root tip (future root). 
• (iv) The root tip is often covered with a root cap (calyptra). 
• (v) Mango, apple, radish, rose, etc., are some dicot plants. 
• Structure of monocotyledonous embryo (i) A typical monocotyledonous embryo consists of one cotyledon. (ii) The cotyledon is situated on one side (lateral) of the embryonal axis and is called scutellum. (iii) The radicle and root cap are situated at the lower end of embryonal axis in an undifferentiated sheath called coleorhiza. (iv) The shoot apex and few leaf primordia are enclosed in a hollow foliar structure in epicotyl region called coleoptile. (v) The portion of the embryonal axis above the level of attachment of scutellum is called epicotyl. (vi) Grass, banana, bamboo, palm, etc., are some monocot plants.

Seed

• It is the fertilized ovule formed inside the fruits.

• It consists of seed coat (hardened ovule integuments), cotyledons and an embryonal axis.

• Two types of mature seeds are.

1. Non-albuminous in which endosperm is completely consumed, e.g., in pea and groundnut.
2. Albuminous that retain part of endosperm, e.g., wheat, maize and barley.

• In some seeds, remnants of nucellus are persistent which is called perisperm, e.g., black pepper and beet root.

• Micropyle of the ovule remains as the small pore in the seed coat. It facilitates the entry of oxygen and water into seed during germination.

• Dormancy In this condition, water content reduces, seed become dry, metabolic activities of embryo slow down and the seed may enter into a state of inactivity called dormancy. If conditions are not favorable seed will not germinate and it may germinate, if conditions are favorable.

Fruits

• Ovary develops into fruit and ovule matures into seeds. The wall of ovary becomes wall of fruit, i.e., pericarp.

1. In true fruits, ovary contributes to fruit formation.
2. Fruits may be fleshy such as, guava, orange, mango or dry such as groundnut, mustard, etc.
3. In false fruits, thalamus (swollen end of stems that bear floral parts) also contributes to fruit formation, e.g., apple, coconut, etc. 
4. Parthenocarpy fruits develop without fertilization and are seedless, e.g., banana. 
5. Seedless fruits can be reproduced artificially through the application of growth hormones.

Apomixis and Polyembryony 

• Apomixis is the special mechanism to produce seeds without fertilization, e.g., grass and is a form of asexual reproduction that mimics sexual reproduction and is useful for the hybrid industry. The modes by which apomictic seeds can be produced are agamospermy, adventive embryony, etc.

• Polyembryony is the presence of more than one embryo in a seed. In many Citruses and Mangifera varieties, some of the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo sac and develop into embryos.

FAQ

What are Post-fertilization Definition Structures and Events?

Post-fertilization Definition Structures and Events refer to the processes and structures that occur in plants after fertilization, leading to the development of seeds and fruits.

What are some examples of Post-fertilization Definition Structures and Events?

Examples include embryo development, endosperm formation, seed coat formation, fruit development, and seed dispersal mechanisms.

How does embryo development occur?

Embryo development begins with the zygote formed after fertilization. It undergoes mitotic divisions and differentiation to form the embryo, which eventually develops into a new plant.

What is endosperm formation?

Endosperm is a tissue that provides nourishment to the developing embryo. It is formed by the fusion of male and female gametes or by a process called double fertilization in angiosperms.

How does seed coat formation happen?

Seed coat formation involves the development of protective layers around the embryo and endosperm. These layers help protect the seed from desiccation, mechanical damage, and pathogens.

What is fruit development?

Fruit development is the process by which the ovary of a flower develops into a mature fruit containing seeds. It involves the growth and differentiation of various tissues, including the ovary wall and surrounding structures.

How do seed dispersal mechanisms work?

Seed dispersal mechanisms help in the dispersal of seeds away from the parent plant, increasing the chances of successful germination and establishment of new plants. Examples include wind dispersal, animal dispersal, and water dispersal.