The fusion that occurs between a male and female gamete in plants in order to be developed into a diploid zygote is termed as fertilisation. Once the fertilisation process is complete, other phenomena or events occur in order to form seed from zygote, this occurrence of events after fertilisation is termed as post fertilisation.
The post fertilisation events includes
1) Reproductive structure development
2)Embryo development
3)Ovules maturing into seed
4)Ovary maturing into fruit
Endosperm
This is a product of triple fusion and develops from the central cell of the embryo sac. It’s typically a triploid tissue. The cells of this tissue are stuffed with reserve food materials and are used for the nutrition of the developing embryo. It’s absent in families like the orchid family, Podostemaceae and magnoliopsida family.
Mode of Development of Endosperm
(1) Free nuclear reproductive structure development: It’s the most typical sort of reproductive structure development. PEN undergoes sequential nuclear divisions to offer rise to free nuclei. Finally, wall formation begins and makes the reproductive structure a cellular tissue.
Examples: Cotton, maize
(2)Cellular mode of development: Primary reproductive structure nucleus divides persistently and every division is followed by wall formation.
(3) Helobial endosperm formation : The formation of endosperm occurring between the cellular and nuclear type is termed as Helobial endosperm formation.
Example: petunia
The coconut milk from tender coconut is free nuclear reproductive structure (made of thousands of nuclei. The encompassing white kernel is the cellular reproductive structure.
Fate of reproductive structure: Reproductive structure is supposed for alimentation of the embryo. Endosperm will be fully consumed during development of the embryo or it will persist in mature seeds.
Embryo Development
The development of embryo from a cell is termed as embryogeny
(1) Embryogeny in dicot Plants
(a) cell (oospore) divides into 2 unequal cells, larger protective suspensor cell towards micropyle and a smaller embryonal cell (= terminal cell) towards antipodal region.
(b) The protective suspensor cell undergoes cross divisions forming 6-10 celled long protective suspensor.
(c) The primary cell of the protective suspensor (towards micropyle) is giant and known as vesicular or sac cell.
(d) The last cell of the protective suspensor towards the embryo cell is hypophysis. It forms a radicle structure tip.
(e) Embryonal cell divides doubly vertically and once transversally to supply 2 there’d eight-celled embryos.
(f) The epibasal tier forms 2 cotyledons and a plumule whereas hypobasal tier produces solely hypocotyl and most radicles.
(g) For this the measuring device embryo undergoes periclinal divisions manufacturing protoderm, procambium and ground plant tissue. it’s ab initio ball-shaped however with the expansion of cotyledons it becomes unsubdivided then assumes the everyday form.
Structure of a typical dicot embryo
A typical dicotyledonous embryo consists of
- An embryonal axis
- Two cotyledons
Parts of Embryonal axis
- Epicotyl: The portion of the embryonal axis on top of the amount of cotyledons that terminates into stem tip or plumule.
- Hypocotyl: The cylindrical portion below the amount of cotyledons that is not any root tip-or radicle.
The root tip is roofed by plant organ
Embryogeny in Monocotyledons
1) The cell or oospore divides transversally manufacturing a protective suspensor cell towards micropylar finish and embryo cell towards chalazal finish.
2)The embryo cell divides transversally once more into a prime and a middle cell.
3)The terminal cell divides vertically and transversally into a ball-shaped embryo.
Structure of a typical flowering monocot plant embryo
- One seed leaf known as scutellum that’s located towards one aspect of the embryonal axis.
- At its lower finish, the embryonal axis has a radical associated degreed plant organ closed in an uniform sheath known as coleorhiza.
- The portion of embryonal on top of the amount of attachment of scutellum is that of the epicotyl. It’s a shoot apex with few leaf primordia closed during a hollow foliar structure known as coleoptile.
- Remains of second seed leaf occur in some grasses. It’s known as epiblast.
Seed
A fertile ovule is termed a seed. Seeds could also be:
Endospermic/Albuminous seeds: eg. Wheat, maize, barley, coconut, castor
Non-endospermic/Exalbuminous seeds:eg. Pea, bean, groundnut
Perisperm seeds: Seeds within which remains of plant part in seen, the residual persistent nucellus called perisperm, eg. Black pepper, beet
Structure of Seed: A typical seed consists of
- Seed coat
- Endosperm
- Embryo
Dormancy and Seed Germination
- Dormancy: It’s a state of inactivity of embryo once the seed isn’t able to germinate
- Germination: The power of a seed to supply a seeding in presence of favourable condition
Advantages of Seed to Angiosperms
(1) Seeds have higher adaptive methods for dispersion to new surround.
(2) It’s spare food reserves for nourishment of young seedlings.
(3)Protection is provided to young embryos by the exhausting reproductive structure.
Fruit
(1) A ripe ovary is termed a fruit.
(2) The wall of the ovary forms a pericarp.
Fruits might be:
- True fruit
- False fruit
Parthenocarpic fruit: The first stimulation for fruit development comes from polarisation whereas the second stimulation is received from developing seeds and therefore the third stimulation is provided by the provision of nutrients.
Conclusion
Triple fusion leads to formation of reproductive structure from the central cell of the embryo sac cell to the embryo. Dicot have 2 seed leaves and flowering plants have just one seed leaf that is in the lateral aspect. The dicot embryo contains an embryonal axis and 2 seed leaves. The ovules change into seed. The ovary develops into fruit.