Double fertilization is the process found in angiosperms in which out of the two male gametes released inside the embryo sac, one fuses with the egg cell (syngamy) and another fuse with secondary nucleus (triple fusion).
Megasporogenesis is the process of formation of megaspores from the megaspore mother cell.
In the hypodermal region of nucellus towards the micropylar end develops a primary archesporial cell.
Dr. T. Annie Sheron
Annie Sheron
Kakatiya Government College
Anther culture:- the in vitro culturing of anthers containing microspores or immature pollen grains on a nutrient medium for the purpose of generating haploid plantlets.
Culturing anthers for the purpose of obtaining Double Haploid is not easy with many field crop species, particularly with the cereals, cotton, and grain legumes.
The Shoot apex is also known as the terminal bud of plants that grows from 0.1-1.0 mm and consists of the apical meristem, developing leaves and the immediate surrounding leaf primordial. The shoot apex is present in both dicot and monocot plants.
Double fertilization is the process found in angiosperms in which out of the two male gametes released inside the embryo sac, one fuses with the egg cell (syngamy) and another fuse with secondary nucleus (triple fusion).
Megasporogenesis is the process of formation of megaspores from the megaspore mother cell.
In the hypodermal region of nucellus towards the micropylar end develops a primary archesporial cell.
Dr. T. Annie Sheron
Annie Sheron
Kakatiya Government College
Anther culture:- the in vitro culturing of anthers containing microspores or immature pollen grains on a nutrient medium for the purpose of generating haploid plantlets.
Culturing anthers for the purpose of obtaining Double Haploid is not easy with many field crop species, particularly with the cereals, cotton, and grain legumes.
The Shoot apex is also known as the terminal bud of plants that grows from 0.1-1.0 mm and consists of the apical meristem, developing leaves and the immediate surrounding leaf primordial. The shoot apex is present in both dicot and monocot plants.
Wall layers of anther have different functions most importantly they help in providing nutrition to developing pollens and also help in anther dehiscence.
Apomixis in flowering plants is defined as the asexual formation of a seed from the maternal tissues of the ovule, avoiding the processes of meiosis and fertilization, leading to embryo development.
The ovules is also known as megasporongia which are borne on a cushion-like tissue called placenta in the ovary. One or more than one ovules are present inside the ovary.
Wall layers of anther have different functions most importantly they help in providing nutrition to developing pollens and also help in anther dehiscence.
Apomixis in flowering plants is defined as the asexual formation of a seed from the maternal tissues of the ovule, avoiding the processes of meiosis and fertilization, leading to embryo development.
The ovules is also known as megasporongia which are borne on a cushion-like tissue called placenta in the ovary. One or more than one ovules are present inside the ovary.
Fertilization is the process of fusion of the female gamete, the ovum or egg and the male gamete produced in the pollen tube by the pollen grain. Fertilization in flowering plants was discovered by Strassburger in 1884.
Flowers are the reproductive structures of angiosperms. They vary greatly physically and are of great diversity in methods of reproduction. The process of fertilization in plants occurs when gametes in haploid conditions meet to create a zygote which is diploid.
The male gametes of the flower are transferred on to the female reproductive organs through pollinators. The final product of this process is the formation of embryo in a seed.
In this lesson you will learn about :
1) What is Fertilization?
2) The Pollen Grain (Male Gamete)
3) The Ovule (Containing Female Gamete)
4) Microsporogenesis and Megasporogenesis
5) Germination of Pollen Grain
6) Double Fertilization
7) Post Fertilization Events
I hope this document is helpful to you. Please share the document with your friends if you think this will benefit them. Get ready for the next lesson. Thanks.
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Procedure for release of the varieties at Central level
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ICAR NET, ARS & STO (T-6)
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PLANT SCIENCE: Seed Science and Technology
TITBITS 2: Sporogenesis, Gametogenesis, Fertilization & Seed
Development
Prepared by
Dr. K. Vanangamudi
Formerly Dean (Agriculture),
Dean Adhiparasakthi Agricultural College,
Professor & Head,
Seed Science & Technology, TNAU, Coimbatore
2. Reproduction - process by which living organisms give rise to offspring of
similar kind (species).
In crop plants, mode of reproduction is of two types, viz.
1) Sexual reproduction
2) Asexual reproduction
Sexual reproduction
Multiplication of plants through embryos which have developed by fusion of male
and female gametes
Ovule development
Development of ovule occurs within the ovary, which provides a location for
nurture and development of the female gametophyte
Ovule growth begins as a small outgrowth within the nucellus.
Secondary outgrowths,orcollars(integuments),soonappear aroundtheperiphery
of the nucellar outgrowths and envelop it.
Consist of the inner and outer integuments and ultimately become the testa
(seed coat) of the mature ovule.
Funicle, hilum, chalaza and raphe
Developing ovule is commonly attached to placenta by the funiculus.
Scar on the ovule made where the funiculus detaches at maturity - hilum.
Point where the integuments meets at the nucellar apex is the micropyle, and
the region of integumentary origin and attachment, usually opposite the
micropyle, is the chalaza.
Between chalaza and hilum of many species is an area known as the raphe.
3. Nucellus
Nucellus provides tissue for the origin and nature of the female gametophyte,
from archesporial cell to the mature megagametophyte.
Originates from ovary tissues and provides site of archesporial cell origin.
Integuments
Nature and thickness of the integuments vary considerably among species,
depending on their role in contributing to embryo sac and ovule development.
Micropyle
Integumentary pore or opening in the ovule through which the pollen tube
grows to fertilize the egg cell of the female gametophyte.
Epistase
Development of well-defined nucellar or integumentary tissue in the micropylar
region of the seed of certain species.
Cells adjacent to the micropyle may show a marked elongation.
SEXUAL REPRODUCTION
Sporogenesis
Production of microspores and megaspores
In anthers, microspores are formed through microsporogensis
In ovules, the megaspores are formed through megasporogenesis.
Gametogenesis
Production of male and female gametes in the microspores and megaspores.
Microsporogenesis
Sporophytic cells in the pollen sacs of anther which undergo meiotic division to
form haploid i.e., microspores are called microspore (MMC) or pollen mother
cell (PMC)
Each PMC produce four microspores and each microspore after thickening of
the wall transforms into pollen grain.
4. Microgametogenesis
Production of male gametes or sperm.
On maturation of the pollen, microspore nucleus divides mitotically to produce a
generative and a vegetative or tube nucleus.
Pollen is generally released in this binucleate stage.
Reach of pollen over the stigma - pollination.
Generative nucleus undergoes another mitotic division to produce two male
gametes or sperm nuclei.
Pollen along with pollen tube possessing a pair of sperm nuclei -
microgametophyte.
Pollen tube enters the embryo sac through micropyle and discharges the two
sperm nuclei.
Megasporogenesis
In angiosperms, seeds originate from meristematic tissue of the ovary wall
called ovule primordial.
From nucellus, one cell develops special characteristics that distinguish it from
adjacent cells.
As this cell increases in size, its nucleus becomes larger and its cytoplasm grows
denser in preparation for cell division (archesporial cell).
First division results in a megaspore mother cell and a parietal cell. Usually the
parietal cell remains undivided and soon deteriorates; however, in some
species, it undergoes further division and contributes to seed formation.
5. A diploid (2N) megaspore mother cell undergoes a two-step cell division called
as meiosis which (Fig. 2) resulted in four megaspores (haploid (1N) cells), each
having one half the chromosome complement of the mother plant.
Normally, only one megaspore is functional, while the other three
degenerate.
Megagametogenesis
Nucleus of the functional megaspore undergoes three mitotic divisions to produce
eight or more nuclei.
The megaspore nucleus divides thrice to produce eight nuclei.
Three of these nuclei move to one pole and produce a central egg cell and two
synergid cells on either side.
Another three nuclei migrate to opposite pole to develop into three antipodal
cells.
Two polar nuclei remaining in the center, fuse to form the secondary nuclei.
Megaspore develops into a mature female gametophyte - megagametophyte or
embryo sac.
Development of embryo sac from a megaspore - megagametogeneis.
Fertilization
Fusion of one of two sperms with egg cell producing a diploid zygote
Fusion of the remaining sperm with secondary nucleus leading to formation of a
triploid primary endosperm nucleus - triple fusion.
6. Seed development
Embryo sac may be ellipsoidal, elongated or variously bent in shape.
Longitudinal axis extends from chalaza to micropyle and through antipodal cells,
the endosperm nucleus and the egg apparatus.
Morphologically, micropyle is at upper end of the embryo sac.
As embryo sac is growing, it requires a constant nutritive supply, which is provided
through the chalaza, establishing a polar gradient from the antipodal to the
micropylar end.
Also obtained from the nucellus and integumentary layers directly through the
wall of the embryo sac.
Embryogeny
7. After sexual fusion or syngamy, a brief period of reorganization occurs, during
which the large vacuole gradually disappears, with the zygote cytoplasm
becoming more homogeneous and the nucleus large.
Lines of polarity in preparation for future division and growth already exist in
embryo sac having been established in the unfertilized egg.
The still undivided zygote typically elongates along the horizontal axis, and
small vacuoles become evenly distributed through the cytoplasm.
1. Globular stage
Globular stage of embryo development precedes the cotyledon development.
Embryo is spherical in shape. Suspensor also develops along with embryo.
2. Heart stage
Globular embryo develops into two lobed form and looks like a heart.
Suspensor acts as an “umbilical cord” providing nutrients to the embryo.
3. Torpedo stage
Cotyledons and axis elongate, enlarge and grow longer.
Embryo may remain straight or became curved.
4. Mature embryo
As the embryo mature, cotyledons curve and provide nutrition to plant, enough to
get plant started with photosynthesis.
Suspensor disappears when cotyledons enlarge and mature.
Endosperm has been used for nutrients for the development and maturation
of cotyledons and embryonic axis.
8. Endosperm development
Endosperm is the principle nutritive support for the embryo of many species
(especially monocotyledons) during both seed development and germination.
Provide nutrition for the developing embryo; therefore, its composition is
compatible with the embryo’s needs.
But, endosperm must also draw its nutritive support from embryo sac and
surrounding tissues.
Net effect is to surround embryo with a rich nutritive tissue from which it can
draw for development and growth.
Creates competition for nutrients, both within and outside the embryo sac.
Types of endosperm development
Division of the primary endosperm nucleus yields micropylar and chalazal
chambers
When only one develops, the other is crushed and soon degenerates.
Classification depending on the sequence of nuclear division and cell wall
formation.
Cellular endosperm
Each nuclear division is accompanied by cell wall formation.
Nuclear endosperm
Characterized by nuclear divisions unaccompanied by cell wall formation.
Nuclei may remain free or may later be separated by cell walls that form in one of
the three ways:
(1) one to three layers of cell wall may form around the periphery, with free nuclei
inside
(2) A cell wall may form in the micropylar area, with the rest remaining in a free-
cell state, or
(3) Entire endosperm may be filled with walled cells.
9. Helobial endosperm
Intermediate between nuclear and cellular types.
Free nuclear divisions occur, but cell wall formation accompanies nuclear division
in some parts of the endosperm as well.
Endosperm haustoria
Nutrient gathering outgrowths called haustoria.
May develop at either the micropylar and chalazal ends and reach into the
nucellar, integumentry, or even ovary tissue.
Branch into several prominent lobes, or diverticulae.
When local food supply is exhausted, haustoria lobes terminate and become
crushed by further endosperm and embryo growth.
The mature endosperm
Monocotyledonous endosperms usually reach their maximum morphological
development at physiological maturity.
In dicotyledonous species, endosperm may not develop or may be used up by
developing embryo.
Seed with little or no endosperm are exalbuminous.
Well-developed endosperm (or perisperm) are known as albuminous.
Some species have a well developed chalazosperm, in which both the nucellus
and endosperm disappear during development and chalazal tissue proliferates
and forms storage tissue.
Outermost layer of the endosperm is known as the aleurone layer.
Become thickened and filled with protein granules.
Functions: both as storage tissue and for secretion of hydrolytic enzymes,
which upon activation during germination help to break down storage tissue.