Pollination and fertilization in plants is a multi-step process. Pollen is transferred from the anther to the stigma of the flower through pollination, which can be self-pollination or cross-pollination. Upon reaching the stigma, the pollen grain germinates and the pollen tube grows down through the style until it reaches the ovule. Double fertilization then occurs, where one sperm cell fuses with the egg cell to form a zygote, and the other sperm cell fuses with the central cells to form the endosperm. This provides nutrition for the developing embryo and leads to the formation of seeds.

1. POLLINATION AND
FERTILIZATION IN PLANTS:

2. Complete Flower
Non – Essential Part Essential Part
Calyx Corolla Androecium Gynoecium
Stamen Carpel
Sepals Petals
To help in Pollination
& protection of inner
whorls
To Protect the
Whorls in Bud
condition
Connective
Filament
Anther Ovary
Style
Stigma
Unit
Unit
Function
Function

6.  Sexual Reproduction in flowering plants was first studied by Camerarius.
 A whorl or verticil is an arrangement of sepals, petals, leaves,
stipules or branches that radiate from a single point and surround or wrap
around the stem.
 The transfer of pollen grain from anther to stigma of a flower is called
Pollination. This transfer is achieved through either by biotic (insects,
birds) & abiotic (wind, water) pollinating agents. The process of pollination
occurs only in Gymnosperms and Angiosperms.
POLLINATION

7. SELF AND CROSS POLLINATION:

8.  Generally there are two types of Self- pollination:
 Autogamy – The transfer of pollen grain from anther to stigma of same
flower. Homogamy is the process of anther to stigma of a bisexual flower
mature at the same time which favours autogamy.
Geitonogamy – is the transfer of pollen grains from anther to stigma of a
flower of the same plant. Occurs in bisexual/unisexual flower of Plant.
Cleistogamy is the condition in which the flower fails to open.
Pros: It maintains the parental character and used to maintain pure lines of
hybridisation experiment. It ensures seed production.
Cons: New useful characters are seldom. Variability and adaptability to
change environment is reduced.
TYPES OF SELF POLLINATION:

9. I. Flowers must be bisexual and both the sexes should mature
at the same time i.e., Homogamy.
II. In some cases, flowers are bisexual and cleistogamous i.e.,
remains closed.
III. In some cases, pollination occurs in bud condition before
opening the flower.
CONTRIVANCES:

10. Allogamy is the process when pollen transfer from anther to the
stigma of different flower on different plant it is also called
Xenogamy.
Dichogamy, Dicliny, Herkogamy, Heterostyly and Self- sterility are
the main reasons for adaptations for cross- pollination.
Pros: It introduces genetic recombination and hence variation in
progeny, thereby increases the adaptability of the offspring towards
changing environment. New & useful varieties can be produced.
Cons: Some undesirable characters may creep in the race. It is
highly wasteful because plants will have to produce a large number
of pollen grains.
CROSS- POLLINATION:

11. Stigma
Pollen Grain = Generative nucleus + Tube nucleus
What kinds of things can move
pollen from an anther to the
receptive stigma of a flower?
 Pollination begins when a grain of pollen lands on a receptive
stigma.
 It ends when a pollen tube punctures the embryo sac.

12. Pollen grain
“germinates”.Tube
nucleus forms a pollen
tube which grows down
through the style.
Generative nucleus
Ovule inside the
flower’s ovary

13. The generative
nucleus divides to
create 2 sperm.
The tube nucleus
continues to lengthen
the pollen tube

14. The tube nucleus disintegrates when
it reaches the ovule. The 2 sperm
continues towards, down of the
pollen tube and eventually reach the
ovule as well.

15. Ovule
Integuments
Embryo sac
2 Sperm
Egg nucleus
Polar nucleus
(Central cell)
Pollen
tube

16.  The pollen grains from one species fails to germinate on the stigma of
another species. This is known as Interspecific incompatibility.
 Intra- specific incompatibility occurs when incompatibility occurs within
the members of species.
 Intra- specific incompatibility between the pollen and the stigmas of the
same plant or another plant termed as Self- incompatibility. It blocks
fertilization between 2 genetically similar gametes increasing the
probability of new gene combination by promoting auto crossing.
 Self- incompatibility responses is genetically controlled by single genetic
locus (S) with multiple alleles.
 There are two quite different types of self- incompatibility:
 Gametophytic Self incompatibility (GSI)
 Sporophytic Self incompatibility (SSI)
SELF- INCOMPATIBILITY

17.  This occurs when the S allele of the pollen grains matches either of the S
allele of the stigma. In this case, pollen tube begins developing but stops
before reaching the micropyle. For Eg., Solanaceae, Rosaceae etc.
 The 2 common mechanism of GSI are the RNAse mechanism and S-
glycoprotein mechanism.
 In RNAse mechanism, elongation of pollen tube stops within the style.
 In S-glycoprotein mechanism, the female determinant is small and
extracelluar molecule expressed in the stigma & male determinant in cell
membrane receptor.
 The interaction between male & female determinants transmits a cellular
signal into the pollen tube resulting in a strong influx of Calcium cations.
The influx of Ca+ ions arrest tube elongation.
GAMETOPHYTIC SELF INCOMPATIBILITY
(GSI):

19.  It occurs when one of the two alleles of the pollen producing
sporophyte matches one of the S alleles of the stigma.
 In SSI, the male determinant expressed in the diploid cells of the
anther tapetum and their products added to the pollen as a constituent
of the pollen coating.
 In Brassica, the male determinant is a cysteine-rich protein located in
the pollen coat & is called the S-locus cysteine-rich protein (SCR).
The female determinant is a serine/threonine receptor kinase, called
S- locus receptor kinase (SRK), located in the plasma membrane of
Stigma cells.
 Each SRK recognizes and binds only to its cognate SCR. Binding of SCR
to SRK causes auto-phosphorylation of the receptor. Phosphorylation of
the SRK receptor initiates a signaling cascade that inhibit pollen
hydration and germination.
SPOROPHYTIC SELF INCOMPATIBILITY
(SSI)

21. Cell signaling regulates recognition of pollen by the stigma, migration of pollen tubes
through the pistil, delivery of sperm to the ovules, and finally, co-ordinated development of
the zygote, endosperm, seed, and fruit. In this review, we summarize recent insights into
the mechanisms that control pollination and fertilization.

22.  How do SLG and SRK enable plants to reject incompatible pollen?
 Current models propose an interaction with a pollen-specific S locus gene,
initiating a phosphorylation cascade that results in pollen rejection.
Although the SI response is often accompanied by a rapid and localized
production of b-1,3 glucan, or callose, in the stigma, surprising recent
studies demonstrate that callose is not required for SI.

23. PLANT LIFE CYCLE & ALTERNATION OF
GENERATION:
 In plants both haploid and diploid cell can divide by mitosis. This abilities
leads to the formation of different plant bodies – Haploid & Diploid.
 The Haploid plant produces gamete by mitosis. This plant body represents
gametophytic stage. Following fertilization the zygote can divide by
mitosis to produce a diploid sporophytic plant bodies, haploid spore
produces by this plant body by meiosis.
 Therefore, according to the division three types of plant life cycle:
1) Haplontic
2) Diplontic
3) Haplo – Diplontic : This type of life cycle is present in bryophytes. Here,
the sporohytes totally or partially depends on gametophyte for its
anchorage and nutrition.

24. The dominant photosynthetic phases
gametophyte produced by haploid
spores. The gamete fuses & produced
on diploid zygote they represents the
sporophytic generation. Meiosis in the
zygote results in the formation of
haploid spores.
The diploid sporophyte is the dominant
photosynthetic phase of plants.
gametophyte produced by haploid spores.
The gametophytic phase is represented
by single to few cells called haploid
gametophyte. This type of life cycle
represented by all the seeds bearing plant.

25. OVERVIEW OF FERTILIZATION & POLLINATION

26.  The fusion of male gamete with the female gamete is called
Fertilization. The phenomenon of fertilization was first reported &
found by Eduard Strasburger in 1894.
 The male gamete are brought to the egg by a pollen tube the
phenomenon is known as Siphanogamy.
 Fertilisation cccurs in 4 main stages:
 A) Germination of pollen tube on stigma.
 B) Growth of Pollen tube.
 C) Pollen tube entry into embryo sac.
 D) Fusion of Gametes.
FERTILISATION

27. THE STEPS IN POLLINATION & FERTILIZATION
OF FLOWERING PLANT

30.  The pollen tube always enters the embryo sac at the micropyler
end. Inside the embryo sac on male gamete fuses with the egg
to form diploid zygote. This process is known as Syngamy.
 The other male gamete fuses with secondary nucleus to form
triploid primary endosperm nucleus; this process is known as
Triple Fusion.
 The occurance of syngamy and triple fusion simultaneously in
angiosperm is called Double Fertilisation.
 Double fertilisation is first reported by S.G.Nawaschin.
DOUBLE FERTILIZATION

31. Angiosperm
Life Cycle

32. Egg (n) Male gamete(n) Zygote (2n) Embryo
Secondary
nucleus
(2n)
Male gamete(n)
Primary
endosperm
nucleus
(3n)
Endosperm
Syngamy Triple Fusion Double Fertilization
Triple
fusion
Syngamy

33.  The female gametophyte stops its growth at 8-nucleated stage,
further growth continues after double fertilization.
 Syngamy leads a diploid zygote which later on changes into embryo &
triple fusion makes endosperm which provides nutrition to the
developing embryo. Thus, double fertilization is necessary for the
formation of viable seeds.
 Secondary nucleus stops its division before fertilization so, the triple
fusion induces dormant nucleus to regain its division power.
 The formation of endosperm is mainly related to its need which arises
after fertilization i.e., particularly for developing embryo.
SIGNIFICANCE OF DOUBLE
FERTILIZATION:

34. POST-FERTILIZATION EVENTS:
BEFORE AFTER
CALYX, COROLLA FALL OFF
ANDROCEIUM, STYLE FALL OFF
STIGMA FALL OFF
OVARY FRUITS
OVARY WALL PERICARP
OVULE SEEDS
INTEUMENT SEED COAT
OUTER INTEGUMENT TESTA
INNER INTEGUMENT TEGMENT
MICROPYLE MICROPYLE
FUNICLE STALK OF SEED
EGG CELL ZYGOTE
SYNERGID DISINTEGRATE, DISAPPEAR