This document provides an overview of plant embryology and seed dormancy. It begins with definitions of embryology and the structures studied, including the flower, stamen, anther, and ovule. It describes processes like microsporogenesis, megasporogenesis, double fertilization, and the development of the dicot and monocot embryos. It also discusses seed dormancy types, causes, methods of breaking dormancy both natural and artificial, and the importance of seed dormancy.

1. UNIT VI EMBRYOLOGY
By ,
Pranav Vijay Gadkar,
Assistant Professor,
Department Of Botany,
BNB College Digras.

2. INTRODUCTION
 What is Embryology ?
The Branch of biology which deals with the
formation , early growth and development of living
organism.
 What we study in Plant Embryology?
• Plant embryology studies not only embryonic
development but also the formation of gametes in
generative sphere and fertilization.
• Comparative plant embryology studies
embryological processes in various species in
order to obtain data for systematics and
phylogeny.

3. FLOWER – REPRODUCTIVE
STRUCTURE
 Flower is defined as highly modified &
condensed reproductive shoot of plant.

4. MALE REPRODUCTIVE
STRUCTURE
 STAMEN-

5. STRUCTURE OF ANTHER

6. MICROSPOROGENESIS
 FORMATION OF POLLEN GRAINS-
Meiosis I Meiosis
II
Pollen
Mother Cell
(2n)
Tetrad of haploid
pollen cell
Pollen Grains
Mature Pollen
grain
Exin
e
Intin
e
Germpor
e Haploid
Nucleus

7. Development of Male
Gametophyte
Exine
Germpor
e
Nucleus
Intine
Generative
Cell
Tube
Cell
Generativ
e Cell
Tube
Nucleus
Pollen
tube
Male
Gamet
Tube
Nucleu
s
A) Pollen
Grain
(Microspore)
B) 2 Celled Pollen
grain
C)
Germinating
Pollen grain
D) Male
gametophyte

8. Types of Ovules

9. Structure of Anatropous Ovule

10. Megasporogenesis and
Development of Female
Gametophyte

11. Monosporic Embryo Sac

13. Double Fertilization and Triple
Fusion

14. Development of endosperm
where repeated
free-nuclear
divisions take
place; if a cell wall
is formed it will
form after free-
nuclear divisions.
Commonly
referred to as
liquid endosperm.
Coconut water is
an example of this.

15. Development of endosperm
where a cell-wall
formation is coincident
with nuclear divisions.
Coconut meat is
cellular endosperm.
Acoraceae has cellular
endosperm
development while
other monocots are
helobial.

16. Development of endosperm
Where a cell wall is laid
down between the first
two nuclei, after which
one half develops
endosperm along the
cellular pattern and the
other half along the
nuclear pattern.

17. Development of Dicot Embryo

19.  Two cell stage
 Following fertilization, the zygote and endosperm are present
within the ovule, as seen in stage I of the illustration on this
page. Then the zygote undergoes an asymmetric
transverse cell division that gives rise to two cells - a small
apical cell resting above a large basal cell .These two cells
are very different, and give rise to different structures,
establishing polarity in the embryo.
 apical cell The small apical cell is on the top and contains
most of the cytoplasm, the aqueous substance found within
cells, from the original zygote. It gives rise to
the hypocotyl, shoot apical meristem, and cotyledons.
Basal cellThe large basal cell is on the bottom and consists of
a large vacuole and gives rise to the hypophysis and
the suspensor.

20.  Eight cell stage
 After two rounds of longitudinal division, and one round of
transverse division, an eight-celled embryo is the
result. Stage II, in the illustration above, indicates what the
embryo looks like during the eight cell stage. According to
Laux et al., there are four distinct domains during the eight
cell stage. The first two domains contribute to the embryo
proper. The apical embryo domain, gives rise to the shoot
apical meristem and cotyledons. The second domain,
the central embryo domain, gives rise to the hypocotyl, root
apical meristem, and parts of the cotyledons. The third
domain, the basal embryo domain, contains the hypophysis.
The hypophysis will later give rise to the radicle and the root
cap. The last domain, the suspensor, is the region at the very
bottom, which connects the embryo to the endosperm for
nutritional purposes.

21.  Sixteen cell stage
Additional cell divisions occur, which leads to
the sixteen cell stage. The four domains are
still present, but they are more defined with the
presence of more cells. The important aspect
of this stage is the introduction of the
protoderm, which is meristematic tissue that
will give rise to the epidermis.[7] The protoderm
is the outermost layer of cells in the embryo
proper.[

22.  Globular stage- The name of this stage is indicative
of the embryo's appearance at this point in
embryogenesis; it is spherical or globular. Stage III, in
the photograph above, depicts what the embryo looks
like during the globular stage. 1 is indicating the
location of the endosperm. The important component
of the globular phase is the introduction of the rest of
the primary meristematic tissue. The protoderm was
already introduced during the sixteen cell stage.
According to Evert and Eichhorn, the ground meristem
and procambium are initiated during the globular
stage.The ground meristem will go on to form
the ground tissue, which includes the pith and cortex.
The procambium will eventually form the vascular
tissue, which includes the xylem and phloem.

23.  Heart stage- According to Evert and Eichhorn, the heart stage is a
transition period where the cotyledons finally start to form and
elongate.[7] It is given this name in eudicots because most plants
from this group have two cotyledons, giving the embryo a heart
shaped appearance. The shoot apical meristem is between the
cotyledons. Stage IV, in the illustration above, indicates what the
embryo looks like at this point in development. 5 indicates the
position of the cotyledons.
 Pro embryo stage-This stage is defined by the continued growth of
the cotyledons and axis elongation.In addition, programmed cell
death must occur during this stage. This is carried out throughout
the entire growth process, like any other development.However, in
the torpedo stage of development, parts of the suspensor complex
must be terminated.The suspensor complex is shortened because
at this point in development most of the nutrition from the
endosperm has been utilized, and there must be space for the
mature embryo. After the suspensor complex is gone, the embryo is
fully developed.Stage V, in the illustration above, indicates what the
embryo looks like at this point in development

24. Development of Monocot
embryo

25. Seeds and their significance
The distribution and dominance of angiosperm on earth is due
to seeds
Success of seed as propagule is due to many characteritics
Dormancy
Viability
Reserve food
Protective coat
Dispersal
Edible fruits

26. Suspended Animation (
Dormancy)
 State or a condition in which seeds are
prevented from germinating even under the
favourable environmental conditions for
germination.
 The main reason behind these conditions is
that they require a period of rest before being
capable of germination.
 These conditions may vary from days to
months and even years.
 These conditions are the combination of light,
water, heat, gases, seed coats and hormones.

27. Causes of Seed dormancy
There are certain major causes for the seed dormancy. Listed
below are the few reasons for the seed dormancy.
 Light
 Temperature
 Hard Seed Coat
 Period after ripening
 Germination inhibitors
 Immaturity of the seed embryo
 Impermeability of seed coat to water
 Impermeability of seed coat to oxygen
 Mechanically resistant seed coat
 Presence of high concentrate solutes

28. Types of Seed Dormancy
 The seed dormancy is of following types:
Innate dormancy
 It is the condition of seeds which is incapable of germination even if
conditions suitable for seedling growth are supplied. This inability to
germinate may be due in certain species to the embryo being
immature at the time of dispersal.
Enforced dormancy
 It is the condition of seeds which is incapable of germination due to
an environmental restraint which includes, an adequate amount of
moisture, oxygen, light and a suitable temperature.
Induced dormancy
 This type of seed dormancy occurs when the seed has imbibed
water, but has been placed under extremely unfavourable
conditions for germination. Finally, seed fails to germinate even
under more favourable conditions.

29. Methods of Breaking Seed
Dormancy
 The different methods of breaking dormancy are mentioned below:
The natural breaking of Seed Dormancy
 Nature of dormancy stops when the embryo gets appropriate
environment such as adaptive moisture and temperature. The seed
coat that exists in many species becomes permeable due to the
rupturing of smoothing action of natural agents like microorganism,
temperature, and abrasion by the digestive tract of birds and
animals that feed on these seeds. Other natural methods include:
 Completion of the over-ripening period.
 Leaching of inhibitors present in the seed coat.
 Inactivation of inhibitors by the supply of cold, heat, and light.
 Leaching of the excess and highly concentrated solutes from the
seeds.
 Production of growth hormones which can neutralize the effect of
inhibitors.

30. Artificial Overcoming of Seed
Dormancy
Some of the artificial methods used for breaking seed
dormancy are listed below:
 Action with hot water for termination of waxes, surface
inhibitors, etc.
 Rupturing of seed coats by filing, chipping, or
threshing through machines.
 Exposure to heat, cold or light, depending upon the
type of seed dormancy.
 By applying Hydraulic pressure for 5 to 20 minutes in
order to weaken the tough seed coats.
 Seed coats are treated with concentrated sulphuric
acid for removing all traces of the mineral acid.

31. Treatment to break dormancy in
seeds
 There are separate treatments to overcome dormancy, and they are further
divided into the following groups:
Seed coat treatment
 These treatments make a hard seed coat permeable to water or gases
either by softening or cracking. This process is called scarification. The
treatment can be either chemical or physical in nature.
Embryo treatments
 Stratification: The incubation of seeds at an appropriate low temperature
over a moist layer before transferring to a temperature suitable for
germination.
 High-temperature treatment: Incubation at 40-50 °C for a few hours to a
few days may have an effect in overcoming dormancy in some species. For
instance, rice seeds treated with hot water at 40°C for at least 4 hours.
 Chemical treatments
 Plant growth regulators or other chemicals can be used in induced
germination growth regulators.

32. Seed Dormancy pathway

33. Seed germination

34. Importance of Seed Dormancy
 It follows the storage of seeds for later use by animals
and man.
 It helps in the dispersal of the seeds through the
unfavourable environment.
 Dormancy induced by the inhibitors present in the
seed coats is highly useful to desert plants.
 Allows the seeds to continue to be in suspended
animation without any harm during cold or high
summer temperature and even under drought
conditions.
 Dormancy helps seeds to remain alive in the soil for
several years and provides a continuous source of
new plants, even when all the mature plants of the
area have died down due to natural disasters