SEXUAL REPRODUCTION IN FLOWERING PLANTS

1. RALLI INTERNATIONAL SCHOOL

3. Events in Sexual
Reproduction
Pre-Fertilization
Fertilization or
Syngamy
Post-fertilization

4. Pre-Fertilization
Gametogenesis
- Formation of gametes
Gamete Transfer

5. Male Reproductive Part of a flower
Stamen
Anther [Bilobed] – It has
two theca hence called
dithecous
Filament
T.S. of anther – Tetragonal in shape
Microsporangia – They are four in number.
They develop into pollen Sac.

6. Structure of Microsporangium : Circular in shape
 Protection
 Dehiscence of anther [helps
in opening of anther to
release pollen grains]
 Nourishment to pollen grains]
 It has dense cytoplasm and is
binucleated

7. Microsporogenesis
 Process of formation of microspore in pollen
grains from MMC
 Every cell of sporogenous tissue is MMC
(Microspore Mother Cell)
Pollen Grain / Microspore / Male Gametophyte
(Spherical in shape)

8. Exine
 Made up of sporopollenin
 Resistant to organic material
 Can withstand high temperature, strong acid
and alkali. Hence can be preserved as fossil.
Intine
 Continuous inner layer
 Made up of cellulose and pectin
Vegetative cell
 Bigger, abundant food reserve and irregular
shaped nucleus.
Generative Cell
 Small, dense cytoplasm and spindle shaped
nucleus

9.  In 60% of angiosperms, pollen grains are shed
at this stage (2-celled stage) and in remaining,
generative cell divides mitotically to give rise to
2 male gametes (3-celled stage)
3-celled stage 2-celled stage
Vegetative cell Vegetative cell
2 Male Gametes Generative Cell

10. Female Reproductive Part of a flower
Gynoecium
Monocarpellary (single pistil)
Multi carpellary (More than one pistil)
Pistil is fusedSyncarpous
Pistil is freeApocarpous

11. Pistil
Landing platform for pollen
grain
Elongated slender part
Basal bulged part
Inside ovary we have ovarian
cavity (locule)

12. Megasporangium (Ovule)
Ovule
One
eg. Wheat, paddy,
mango
Many
eg. Papaya, watermelon,
orchids
Figure of Megasporangium (Ovule)

13. Megasporogenesis

14. Pollination
Autogamy Geitonogamy Xenogamy
Pollination – Transfer of pollen grains from anther to
stigma of a pistil
Transfer of pollen grains
from anther to stigma of
a same flower
eg. pea
Transfer of pollen grains
from anther to stigma of
another flower of same
plant eg. cucurbita
Transfer of pollen grains
from anther to stigma of
another flower of different
plant eg. papaya

15. Flower
eg. Viola, Oxalis,
Commelina
Chasmogamous
Exposed anthers &
stigma
Cleistogamous
Closed flowers
Autogamy (Self-pollination)

16. Agents of pollination
Agents of Pollination
Abiotic Biotic
Wind Water
Reptiles Mammals Insects Birds
Animals

17. Adaptation for wind pollination
 Pollen grains are light & non-sticky
 Well exposed stamens & feathery
stigma
 Flowers packed into inflorescence.
 eg. Corn cob-tassels (stigma & style)
Adaptation for water pollination
 Common in algae, bryophytes,
pteridophytes & monocots
 Vallisneria, Hydrilla (fresh water)
and sea grasses like zostera
(marine)
 Exception : water hyacinth & water
lily pollinated by insect or wind
 Pollen grains are long ribbon like
and have mucilaginous covering

18. Adaptation for insect pollination
 Flowers large, sticky and brightly coloured
 Have honey and nectar which act as floral
rewards
 Tallest flower of Amorphophallus provide safe
place (floral reward) for laying eggs.
 Moth & Yucca – Moth deposits its egg and
Yucca in turn gets pollinated

19. Outbreeding devices
 Stops inbreeding depression due
to self pollination
 No synchrony between pollen
release and stigma receptivity
 Anther and stigma placed at
different positions
 Self incompatibility
 Production of unisexual flowers
 Monoecious plants (Male &
Female flowers on same plant)
prevent autogamy but not
geitonogamy
 Dioecious plants prevents both
autogamy and geitonogamy

20. Pollen-Pistil Interaction
 Events from pollen deposition on the stigma until
entry of pollen tube into ovule.
 Dynamic process, incompatible pollens don’t grow
 Compatible pollens develop pollen tubes which
grows through stigma & style to reach the ovary. It
enters the ovule through micropyle and reaches the
synergids guided by filiform apparatus.

21. Artificial Hybridization
 Helps to obtain desirable characters.
 Emasculation – Anthers are removed using forceps
 Bagging – Flower is covered with paper bag
 Re-bagging – Pollen grains dusted on stigma and
the flower covered again
Double Fertilization
Syngamy Triple Fusion
Male gametes fuses with
egg nucleus to form zygote
Other male gametes fuses
with polar nuclei to form
Primary Endosperm Nucleus(PEN)

22. Double Fertilization
Syngamy Triple Fusion
Male gametes fuses with
egg nucleus to form zygote
Other male gametes fuses
with polar nuclei to form
Primary Endosperm Nucleus(PEN)

23. Post-Fertilisation
Development of
• Endosperm
• Embryo
Maturation of
• Ovule(s)  Seed(s)
• Ovary  Fruit

24. Endosperm
 Endosperm development precedes embryo development.
 Primary Endosperm Cell (PEC) formed as a result of triple fusion
undergoes repeated divisions and a triploid endosperm tissue is formed.
 In most of the cases, the PEN undergoes successive nuclear divisions
without cytokinesis, to give rise to free nuclear endosperm.
 Subsequently, cell wall formation starts from the periphery and the
endosperm becomes completely cellular, e.g., coconut, rice, maize,
sunflower, etc.
 Filled with reserve food materials used for nutrition of developing embryo.
 The endosperm may be completely utilised by the developing embryo
before the maturation of seeds as in pea, bean and mustard, etc.

25. Embryo
Dicot Embryo Monocot Embryo

26. Embryo : Development (Embryogeny)
 Develops at micropylar end of the embryo sac where zygote is situated.
 Zygote  Proembryo  mature embryo (globular, heart-shaped).

27. Seed (fertilised ovule)
 It is the final product of sexual reproduction
 Consists of seed coat, cotyledons and an embryonal
axis
 Perisperm: Residual, persistent nucellus. Ex. Black
pepper and Beet
 Integuments of ovules harden to form the seed coat.
 Micropyle facilitates the entry of oxygen and waer
into the seed
 As the seed matures the embryo enters into a state of
dormancy.

28. Fruit (Develops from ovary)
 Wall of the ovary develops into wall of fruit called
pericarp.
 Consists of seed coat, cotyledons and an embryonal
axis
 Fruits may be fleshy ex. Guava, mango
 Fruits may be dry ex. Groundnut and mustard
FRUITS
TRUE FALSE PARTHENOCARPIC

29. Advantages of seeds
 Seed formation is more dependable as fertilization and
pollination does not require water.
 Better adaptive strategies for dispersal
 Have sufficient food reserves.
 Hard seed coat provides protection to the young
embryo.
 Generates new genetic combination leading to
variation.
 Can be stored as food.

30. APOMIXIS
 Apomixis is a mode of reproduction which does
not involve formation of zygote through gametic
fusion.
 Is mechanism of seed production without involving
the process of meiosis and syngamy.
 It plays an important role in hybrid seed
production.
POLYEMBRYONY
 The phenomenon of the development of more than
one embryo in one ovule, seed or fertilized ovum is
called polyembryony.
 Caused due to fertilization of one or more than one
embryonic sac or due to the origination of embryos
outside of the embryonic sac.