UNIVERSITY OF ALLAHABAD

1. UNIVERSITY OF ALLAHABAD
DEPARTMENT OF BOTANY
“Fertilization And Apomixes”
Presented by :-
BRIJESH PRATAP SINGH
(M.Sc. 2nd SEM. )
Presented to:-
Dr. RAJIV YADAV

2. INTRODUCTION :-
 Pollen shed from the anther it has two cells :-
A Generative Cell and A Tube Cell.
 The generative cell Give rise to male gametes.
 One of the male gamete fuses with egg and forms the
zygote. This fusion of male and female gametes is
known as fertilization. The second male gamete fuses
with the two polar nuclei (or secondary nucleus if the
two have already fused ) and forms a triple-fusion
nucleus, called primary endosperm nucleus.

4.  Various event leading fertilization :-
(1) Germination of pollen grains
(2) Formation of pollen tube
(3) Entry of pollen tube into ovule
(a) Porogamy
(b) Chalazogamy
(c) Mesogamy
(4) Entry of Pollen Tube in the Embryo-sac
(5) Movement of sperms toward egg and polar
nuclei
(6) Fusion of gametes

5. (1) Germination of pollen grains-
 Once the pollen grain has landed on the receptive
stigma, its germination starts.
 One of the requirements for germination of the pollen
grain is that it should adhere to the stigmatic surface.
 In plants like Petunia hybrida, Strelitzia reginea & Zea
mays the stigma secretes a sticky and oily exudate and
pollen grains adhere to this stigmatic fluids.
 In Brassica pollen grains stick to the stigmatic papillae
because of a ‘melting together reaction’ with the waxy
coating of the cuticle brought about by cutinase
enzyme.
 In Cosmos pollen grains are attached to the stigmatic
surface by mucilagenous strands.

7.  In some 80 families of angiosperm the stigma has short
papillose outgrowths.
 The surface of these papillose outgrowths is made of
hydrophilic proteins, which keep it moist.
 This help in the hydration of pollen grains.
 The stigmatic papillae collapse after pollination and a
watery substance is formed by degeneration of their
cytoplasm, helps in pollen germination.
 The germination of pollen grains depends upon their
longevity, i.e. the duration for which they remain viable.
 It varies considerably in different species.
e. g. – for 3 minutes in Reseda, 5 min. in Zea mays, 2 hrs
in Beta vulgaris, 12 hrs in Secale cereala, 15 days in Prunus
padus, 35 days in Viola odora & 56 days in Primula elatior
The viability also depends upon moisture and temperature
conditions.

8.  Presence of many hydrolitic enzymes such as acid and
alkaline phosphatase, ribonuclease, esterase & amylase
in the intine of pollen grains play a significant role in
the process of pollen germination.
 Usually pollen grains are monosiphonous i.e. each
pollen grain produces only a single pollen tube, but in
Campanulaceae, Cucurbitaceae, & Malvaceae they are
polysiphonous.
 In Althea rosea as many as 10 pollen tubes from a
single pollen grain have been observed, & in Malva
neglecta the number goes up to 14, only one pollen
tube carries pollen nuclei and others are degenerate at
different stage of development .

9. Monosiphonous
Polysiphonous

10. (2) Growth of pollen tube
 The growth of the pollen tube down through the style
depends upon internal structure of the latter.
 The style of Lilium & Ribes are hollow and secrete a
mucilagenous secretion which help in the passage of
pollen tube.
 Mostly the style is solid and hence passage of tube
involves the secretion of tissue dissolving enzyme
(pectinase) by the growing tip of the tube.
 In Oenothera, Petunia & Datura the pollen tube grows
through the intercellular spaces in the style.
 In Phaseolus vulgaris & P. coccineus, the pollen tube
usually grows in style close to the vascular tissue.

11.  When pollen grain germinates, its entire contents move
into the pollen tube.
 The growth of the pollen tube is primarily restricted to its
tip where most of the cytoplasm is concentrated.
 The cytoplasm is restricted to the tip of the pollen tube by
callose plug, which grow centripetally and finally seal the
tube.
 The extreme tip of the pollen tube, which appears as a
hemispherical transparent area under light microscope, is
known as cap block.
 The wall of the pollen tube is made up of cellulose and
pectin.
 Growth of pollen tube in the style is always directed
towards the ovary, such unidirectional growth is perhaps
due to hydrotropic, chemotropic and mechanical factors.

12. (3) Entry of pollen tube into ovule
 On reaching the ovary, the pollen tube grows towards one
of the ovules. It may enter the ovule through one of the
following three routes:
(a) POROGAMY-
When the pollen tube enters into the
ovule through micropyle, it is known as porogamy.
This is the most common mode of pollen tube entry into the
ovule.
(b)CHALAZOGAMY-
When the pollen tube enters the ovule
through its chalazal end, is called chalazogamy
It is common in Betula, Juglans regia, Casuarina, Ostrya and
Pterocarya.

13. (c)MESOGAMY-
When the pollen tube enters the ovule
through integuments, the condition is described as
mesogamy.
 Alchimella, Cucurbita & Populus are some examples of
mesogamy.

15. (4)Entry of pollen tube in the
embryo-sac
 Irrespective of the place of entry into the ovule, the
pollen tube always enters the embryo-sac through the
micropylar region.
 It may enter the embryo-sac via one of the following
routes-
 (a)between the egg cell and one of the synergids
without destroying the latter,
 (b)between the wall of the embryo-sac & one or both
the synergids,
 (c)between the two synergids without destroying
either of them,
 (d)directly penetrates one of the synergids,

16.  Usually a single pollen tube enters in an embro-sac but
3-5 pollen tubes have been observed in a single
embryo-sac in some taxa

17. (5)Movement of sperms toward
egg and polar nuclei
 Contents of the pollen tube are released in one of the
synergids, and as the egg cell and synergids are in close
contact, sperm do not have to travel long.
 In some embryo-sac, where synergids are absent (e g
Plumbago & Plumbagella types), the pollen tube
penetrates the embryo-sac in between the wall of the
embryo-sac and egg cell.
 The sperms show amoeboid movements, one of the
male gametes moves towards the egg and the other to
the polar nuclei.

18. (6)Fusion of gametes
 Fusion of one of the male gametes with the egg is
known as syngamy or true fertilization. It results in the
formation of a diploid zygote.
 The union of second male gamete with the polar
nuclei results in the formation of primary endosperm
cell and constitutes double fertilization.
 Most of the embryo-sacs have two polar nuclei, double
fertilization involves fusion of three nuclei i.e. triple
fusion.
 Gerassimova-Navaschina(1960, 1982)
 recognized following three types of gametic fusion-

19. (a)Pre-mitotic-
In this type the sperm nucleus attains its
mitotic rest after penetrating the egg nucleus but prior
to the initiation of the first zygotic nucleus.
 This type of fusion is common in Poaceae, Asteraceae,
Ranunculaceae, Solanaceae & Cucurbitaceae.
(b)Post-mitotic-
In this type of syngamy the sperm nucleus
completes its mitotic cycle while in contact with the
female nucleus.
 It is also known as zygotic mitosis.
 It can be seen in Lilium & Fritillaria

20. (c)Intermediate-
In some taxa like Impatiens, Mirabilis &
Tradescantia the nucleus fuses with the egg nucleus
after completing telophase of its previous mitosis.

21. (7)Interval between pollination
and fertilization
 Time gap between pollination and fertilization is from
2 hr to 12 days or even more.
 Syngamy and triple fusion usually begin
simultaneously; wherever these processes are
disjunctive, it is mostly the triple fusion which comes
off earlier.
 The actual process of nuclear fusion is also more brisk
in the central cell than in the egg.

22. X-bodies
 After the discharge of pollen tube contents into the
embryo sac, two darkly stained bodies have been
observed in the synergids penetrated by the pollen
tube, or in the vicinity of the egg apparatus.
 These bodies, called x-bodies by S. G. Nawaschin, have
been interpreted as decomposition products of
vegetative nucleus.

23. Apomixis :-
 According to H. Winkler(1908), the term apomixis
(away from mixing) refers to the substitution of sexual
reproduction by any such method which does not involve
meiosis(production of gametes) and syngamy(formation
of zygote).
 Apomixis (Apo=without; mixis=mingling) and plants are
apomictic plant.
 Two Main categories:-
a) Agamospermy
b) Vegetative Reproduction

24. Agamospermy :-
Plants belonging to this category have retained seed for
propagation but embryo is formed by some process in which
normal meiosis and syngamy have been eliminated.
a) Adventive embryony:- Embryo arise directly from diploid
sporophytic cells (nucellus or integument).
b) Diplospory:- An archesporium differentiates, but MMC
develops into an unreduced(absence of meiotic) embryo
sac. The embryo is formed by unfertilized egg
(parthenogenesis) or some other cell of embryo sac
(apogamy).E.g. Aerve tomentosa.
c) Apospory:- somatic cell in the nucellus directly formed
unreduced Embryo.

25. Vegetative Reproduction:-
New individual is arises from group of
cell, where neither embryo nor seed are
produced.
 Reproduction by bulbs, bulbils,
tubers, runners and suckers and these
propagules are formed by sporophyte
only.

26. Types Of Apomixis:-
 Dr. P. Maheshwari(1950) sub-divided apomixis in 3 types:-
a) Non-recurrent:- Embryo arise from an unfertilized egg
(haploid parthenogenesis) e.g., Epipactus lantifolia or
from gametophyte cell(haploid apogamy).E.g. Nicotiana
tobbacum .
 Acc. To Maheshwari egg may fails to fertilize due to
following cause-
Absence of pollen tube, inability of the tube discharge
its contents, an insufficient attraction between male
and female nuclei, an early the generation of sperm etc.

27. b) Recurrent:- Embryo sac arise from archesporial cell(generative
apospory) Eg. Partheium argentatum. or from nucellus(somatic
apospory)Eg. Hieracium
c) Adventive embryony:- Diploid tissue of sporophyte give rise to
embryo, also called sporophytic budding. Eg. Euphorbia dilcis

28. Significance :-
 It offers possibility of indefinite propagation, which may
be highly heterozygous or sexually Sterile.
 Apomictic genera are polyploids, By Strasburger.
 According to Ernest apomictic plant serve as hybrid.
 Haploid parthenogenesis helps in obtaining true
breeding homozygous material.
 Apomictic crop plants are citrus,mango and black
berries.
 An apomixis does not involve meiosis, there is no
segregation and recombination of chromosome. Thus is
useful in preserving desirable characters for indefinite
periods.

29. REFERENCES:-
A TEXT BOOK OF BOTANY “ANGIOSPERMS”:-
SINGH. PANDEY. JAIN
A TEXT BOOK OF BOTANY- Dr. R.K. SINGH

30. BRIJESH PRATAP SINGH