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Reproduction
Life span: Birth to death.
No organism is immortal, death is a certainly except in case of unicellular organism immortal, their
growth and reproduction is the same
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Tortoise : 100-150 yrs
Parrot : 140 yrs
Elephant : 65 yrs
Horse : 60 yrs
Crocodile : 60 yrs
Cow : 20-25 yrs
Dog : 20 yrs
Fruit fly : 2 weeks
Butterfly : 1-2 weeks
Banyan: 1000-2000 yrs. Mango tree has less life span than peepal.
Rose : 5-10 yrs
Banana: 1-2 yrs. Rhizome has life span of 20-25 yrs.
Rice : 4 month
Reproduction – A biological process in which organism gives ie to young ones (offspring) similar to itself
based on the no of organism participating in reproduction it is of two types
a) Sexual
b) Asexual
Asexual reproduction: when offspring is produced by a single parent with or without the involvement of
gamete formation (Gamete will not fuse), the reproduction is asexual.
Parthenogenesis: female gamete develops into embryo without fertilization ex. Rotifers , honey bees,
some lizards and birds (Turkey)
Monera reproduces only asexually
Protista and monera reproduce by cell division – the parent cell divides to form new individuals
Amoeba and paramecium – binary cell – the parent cell divides into two halves and ach half rapidly
grows into an adult
Yeast – budding
In yeast, the division is unequal and small buds are produced that remain attached initially to the parent
cell which, eventually gets separated and mature into new yeast organism (cells).
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Budding in yeast :- intranuclear mitosis-unequal cytoplasmic division
Binary fission in amoeba :
Thallophytes – algae and fungus reproduce through special asexual reproductive structures called –
mitospores / accessory spores. The most common is Zooospores – motile and without cell wall
Other methods
 Conidia (penicillium)
 Buds (hydra)
 Gemmules (sponge)
Asexual reproduction is the common methods of reproduction in organism in thallophytes and they shift
to sexual methods of reproduction just before the onset [start] of adverse conditions.
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Vegetative reproduction – very fast ; new individual are formed from bodu parts, the units of vegetative
propagation are Runner , Offset, Rhizome, Sucker, Tuber, Bulb [ these are called vegetative
propagules]. Since one parent is involved so it is also asexual
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Vegetative propagation – conserves variation , morphology, vigour for generations
Naturals methods of vegetative reproduvtion : all these exploited by gardners and farmers for
commercial propagation
a) By tuberous roots : sweet potato, dahlia, asparagus, tapioca
b) Leaves : adventitious buds present at the notches at leaf margins of Brophyllum and kalanchoe
c) By stem : buds arise from the nodes present in the modified stems of these plants. When the
nodes come in contact with damp soil or water, they produce roots and new plants
The underground stem modification are also act as organ of perenation to tide over condition
unfavourable for growth
a) Rhizome - ?
b) Corms - ?
c) By underground stem tubers : potato, buds (eyes) at nodes heaping of earth
Nodes contain buds and whwn node comes in contact with damp soil, bud grows producing shoot and
roots develop on those shoots
d) Suckers - ?
e) Runner - ?
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f) Stolon - ?
g) Offset -?
Terror of bengal ? invasive sp ? scourage of water bodies
h)bulbils – agave , oxalis
horticultural methods / artificial methods of propagation :
a) Stem cutting : rose , sugarcane
b) layering : roots induced on stem before separating from the plant, the lower branches of stem is
bend and buried in ground which induces roots in it. Ex strawberry , jasmine, cherry , grapevine.
c) Grafting : done only in dicots [ cambium]
Scion of a desirable variety / having superior characters is grafted on roots rubber , mango ,
guava.
Asexual (vegetative) a well as sexual modes of reproduction are exhibited by the higher plants.
Only sexual mode reproduction is present in mode of the animals.
Sexual reproduction: prokaryotes doesn’t have sexual reproduction
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In sexual reproduction, two parent (opposite sex) participate in the reprosctive process and also
involve fusion of male and female gametes.
One parent ma also perform sexual reproduction-but it should be bisexuals
SR is a slow, complex and elaborate process as compared to ASR, but have benefits of variation.
There are three phases in the life of an organism
1. Juvenile and vegetative phase
 all organism have to reach a certain stage of growth and maturity in their life before they can
reproduce sexually.
 That period of growth is called the juvenile phase.
 It is known as vegetative phase in plants.
 This phase is of variable durations in different organism.
2. Reproductive phase
 the end of juvenile / vegetative phase marks the beginning of the reproductive phase.
 It can be seen easily in the higher plants when they come to flower.
Vegetative phase of
a) Marigold
b) Rice
c) Wheat
d) Coconut
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e) Mango
In some plants where flowering occurs more than once, what would you call the inter – flowering period
– juvenile or mature ?
Why do you think the availability of fruits like mango, apple, jackfruit , etc. is seasonal ?
3. Senescent phase : after reproductive phase , till death
In both plants and animals, hormones are responsible for the transition between the three phases.
 The annual and biennial types plants: they shoe clear cut vegetative, reproductive and
senescent phases.
 But in the perennial species it is very difficult to clearly define these phases.
 Unusual flowering phenomenon: some of them such as bamboo species flower only once in
their life time, generally after 50-100 yrs, produce large numbers of fruits and die.
Flowering in strobilanthus kunthiana
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This plant – neelkuranji, flower once in 12 years.
This plant flowered during September-october 2006.
Its mass flowering transformed large tracks of hilly areas in kerala , Karnataka and tamil nadu
into blue stretches and attracted a large number of tourist.
Monocarpic plants: bamboo amnd neelkuranji
Polycarpic plants: they have an inter flowering vegetative growth
Even though the structures associated with sexual reproduction in different plants are indeed very
different.
The events of sexual reproduction though elaborate and complex, follow a regular sequence
Events in the sexual reproduction :
a) Prefertilistion – sporogensis in angiosperms
b) Fertilistion
c) Post fertilization-embryogeny and seed formation in angio
Pre fertilization events :
Two main events are: gametogensis and gamete transfer
Gametogensis : formation of male and female gametes. Gametes are always haploid.
Homogametes / isogametes:
Heterogametes : aniso and oogamy
Ex. Isogamy : spirogyra ulothrix, chlamydomonas
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Anisogamy :
Oogamy (common) : red algae, volvox , oomycetes
Brown algae and chlamydomonas
Homothallic / monecious : concept in angiosperm and non flowering plants with examples.
Heterothallic / dioecious condition : cocept in angiosperm and non floering with examples.
Gamete transfer
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In several simple plants like algae, bryophytes and pteridophytes, water s the medium through
which this gamete transfer takes place.(zoidiogamy)
A large number of the male gametes, however, fail to reach the female gametes.
To compensate this loss of male gametes during transport , the number of male gametes
produced is several thousand times the number of female gametes produced .
In seed plant : pollen grain carries male gametes, and by pollination that are transferred , siphonomy
[to get rid of water].
Fertilization : the most vital event of sexual reproduction
External fertilization : ex. Algae, fishes and amphibians. Both gamete produced in large number.
Organism exhibiting external fertilisation show great synchrony between the sexes and release a large
number of gamete into the surrounding medium ( water) in order to enhance the chance sof syngamy.
This happen in the bony fishes and frogs where a large number of offspring are produced.
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A major disadvantage is that the offspring are extremely vulnerable to predators threatening their
survival up to adulthood.
Internal fertilization : in fungus , bryo, pterido, gymno,angio. Less egg and more sperms
Case of bron algae- oagamous species .(red algae)
Usually motile male gametes, except non motile male gamete in seeed plant here they are carried by
pollen tubes
Post fertilization events : in organism belonginbg to fungi and algae , zygote develops a thick wall that
is resistant to desssication and damage- ( this structure called zygospore).
It undergoes a period of rest before germination.
In organism with haplontic life cycle , zygote divides by meiosis to form haploid spores that grow into
haploid individuals.
Case of red algae - complex post fertilization changes
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In flowering plants :
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The zygote is formed inside the ovule.
After fertilization the sepals, petals and stamens of the flower wither and fall off.
Can you name a plant in which the sepals remain attached / the pistils however, remains attached to the
plant.
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The zygote develops into the embryo and the ovules develop into the seed.
Endosperm provides nutrition.
The ovary develops into the fruit which develops a thick wall called pericarp that is protective in
function.
After dispersal, seeds germinate under favourable conditions to produce new plants.
Concept of haploid and diploid number
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Embryogenesis in embryophytes.
Embryology of flowering plants
PANCHANAN MAHESHWARI(1904-1966)
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F/o plant embryology in indai and F/o TC studies in india.
His work ob test tube fertilization and intra-ovarian pollination won worldwide acclaim.
Also authored the book’ An introduction to embryology of angiosperm’
History
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Grew reported the sex organs of the plant : the stamens
Camerarius discovered sexual reproduction
Floriculture – cultivation of flowers
Life cycle – technically haplodiplontic (NCERT – diplontic)
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Microspore is the first cell of gameteophyte generation
Meiosis occur during formation of gmeteophyte from sporophyte
Hetrospory – SAMS,Seed plants-Homospory
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Decision of SR is taken even before flower is formed,
Appropriate photoperiod,sensed by Pfr-Florigen transported to apex.
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Several hormonal (florigen) and structured changes are initiated which lead to the
differentiation and further development of the floral primordium.
The vegetative shoot apex start changing into reproductive apex
Inflorescences are formed which bear the floral buds and then the flowers.
In the flower male and female reproductive structures, the androecium and the gynoecium
differentiate and develop.
Stamens , Microsporangium and pollen grain
1. Stamen :
a) the long and slender stalk called the filament, and
b) the terminal generally bilobed structure called the anther.
c) The number and length of stamens are variable in flower of different species.
Filament : The proximal end if the filament is attached to the thalamus or the petal of the flower.
Anther :
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A typical angiosperm anther is bilobed with each lobe is called a theca. So anther is
dithecous (F-2-2).
Often a longitudinal groove runs lengthwise separating the theca.
Malvaceae shows momothecous anther.
Tissues and their organization in an anther
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The bilobed nature of an anther is very distinct in the tranverse section of the anther.
The anther is a four sided (tetragonal) structure.
It is consisting of four microsporangia located at the corners, two in each lobe.
The microsporngia develop futher and become pollens sacs.
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They extend longitudinally all through the length of an anther and are packed with pollen grain.
Anther cells are haploid, diploid, polypoid.
Structure of microsporangium
In a transverse section, a typical microsporangium appears near circular outline.
It is generally surrounded by four wall layers from outside to inside.
I.
II.
III.
IV.
Epidermis – exothecium
Endothecium / fibrous layer
ML : three cell layers thick, nutritive
Tapetum
The outer three wall layers perform the function of protection and also help in dehiscene of anther to
release the pollen
Tapetum :
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Nutritive in function ; provide nutrition to developing spores / pollen grain.
Cell show : dense cytoplasm, generally multinucleate condition,polyploidy.
Tapetum releases callase enzyme, IAA, pollenkitt.
Makes the exine of pollen by deposting aporopollenin. Ubisch body perform the thickening of
exine of pollen / deposits sporopollenin.
In the end ML and tapetum is finally consumed by the developing sporogenous tissue, and at
maturity only endthecium and epidermis remains.
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Sporogenous tissue :
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When the anther is young, a group of compactly arranged homogenous cells called the
sporogenous tissue occupies the centre of each microsporangium.
The cells of sporogenous tissue become pollen mother cells.
PMC divides by meiosis to form microspore tetrad – cluster of four (Microsporogenesis)
Microspore tetrad – surrounded by callose covering.
As the anther mature and dehydrate. The microspores dissociate from each other and develop
into pollen grains
Callase enz help in separation
Inside each microsporangium several thousand of microspores or pollen grains are formed that
released with the dehiscence of anther [ largest number of haploid cells occur in microsporagia,
all are genetically different]
250 sporocyte will produce 1000 PG
Abnormalities :
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Polyspory : formation of more than 4 spores per meiosis
Pollinium : all the PG of an anther lobe remain together in a sac called pollinium. Ex
asclepiadaceae-calotropis, orchidaceae.(most advanced monocot).
Palynology
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It refers to the study of morphology of PG
Longest pollen : sea grass- zostera it has filamentous pollen
Normally pollen spherical and is 25-50 𝜇𝑚 in size usually it looks yellowish powdery
In scanning electron microcope we can observe the variety of architecture – sizes, shapes,
colours, design- seen on the pollen grains of different plants. These pattern and design are due
to exine.
 PG has a prominent two layered wall.
a) Exine
b) Intine
 Exine : the hard outer layer called the exine is made up mof sporopollenium, a hydrophobic
carotenoids which is one of the most resisitant organic material known.
Sporopollenium can withstand high temperature and strong acids and alkali.
No enzyme that degrades sporopollenium is so far known.
Pollen grains are well preserved as fossils because of the presence of sporopollenin.
 PG analysis is done for identifying petroleum deposits.
 Pollen grain exine has prominent apertures called germ pores. Where sporopollenin is absent.for enry of water.
 Question : why do you think the exine should be hard ? what is the function of germs pore ?
Dicot-3GP , monocot-1GP
 Intine : the inner wall of the pollen grain is called the intine.
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it is thin and continous layer made up pf cellulose and pectin.
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Hay fever / seasonal asthma : Is chronic respiratory disorder like asthma, bronchits/ seasonal
asthma due to PG inhalation(anemophilous plants)
parthenium or carrot grass that came into india as acontaminant with imported wheat, has
become ubiquitos in occurrence and causes pollen allergy.
Pollen is rich nutrient as pollen tabelets are used as food supplement, pollen consumption
increases the performance of race horse and athlete
Pollen products are polen shake, syrup and pollen cream
Development of male gameteophyte / microgametogensis
1st division – unequal / asymmetric
a) Vegetative cell / tube cell : VC is large cell, large irregular shape, nucleus, abundant food reseve
b) Generative cell : small, spindle / boat shaped with dense cytoplasm and floats in the cytoplasm
of VC after pollination Gc forms 2 non motile male gamete
 No prothallial cells
 There are 3 cells in mature male gametophyte
 Pollen grains is a partrially developed male gametophyte
 PG released at 2 celled in 60% of the angiosperm,in 40% of angiosperm it is released at 3 cell
stage.
Pollen viability : the viability period is highly variable and to some extent depends on the prevailing
temperature and humidity. In some cereals like rice and wheat – PG lose viability within 30 minute
Solanaceae, leguminoseae, rosaceae - it can live a month
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PG Storage : it is possible to store pollen grains of a large numbers of species for year in liquid
mnitrogen(-196℃). Such stored pollen can be used as pollen banks, similar to seed banks, in crop
breeding programmes.
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Abnormalities :
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PG embryo sac / nemec phenomena: it occurs in hyacinthus
PG apogamy / androgamy / androgenesis : pollen culture is used to produce haploid plant by
tissue culture. In anther culture the occasional diploid cells are the cells of wall of anther
PG sterility / male sterility : unviable PG, Mitochondrial gens and nuclear genes. Unviable PG
Pollination : Transfer of pollen grains (shed from the anther) to the stigma of a pistils is termed
pollination. It is a method of transfer of non motile gametes. Now no need of water for transferring
gametes.
Due to water requirement P&B were restricted to narrow geographical regions. Seed plants could
spread to dry areas due to pollination – Pollination started from Gymnosperms
Depending on the source of pollen, pollination can be divided into three types.
1) Autogamy / ecological self pollination: pollination within the same flower
2) Geitonogamy : transfer of pollen grains from the anther to the stigma of another flower of the
plant. Although geitonogamy is functionally cross-pollination involving a pollinating agent,
genetically it is similar to autogamy since the pollen grains come from the same plant.
3) Xenogamy : [genetical cross pollination – result in hetrozygosity] transfer of pollen grains from
anther to the stigma of different plant. This is the only type of pollination which during pollination
brings genetically different types of pollen grains to the stigma. Ex sunflower
Allogamy / ecological cross pollination / functional cross pollination : pollination with different
flower-require pollinator-geitonogamy and xenogamy are two types of allogamy.
Autogamy adaptions.
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A. Bisexual flower
B. Homogamy-synchrony in pollen release and stigma receptivity and also
C. Chasmogamous : flower is open, anther and stigma are exposed to pollinators but the anthers
and the stigma should lie close to to each other so that self-pollination can occur.
D. Cleistogamous : flowers which do not open at al. in such flowers, the anther and stigma lie close
to each other. When anther dehisce in the flower buds, pollen grains come in contact with the
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stigma to effect pollination. Thus, cleistogamous flower are invariably autogamous as there is no
chance of cross pollen landing on the stigma.
Advantage of cleistogamy : Asssurance of seed set – even in bsence of pollinators.
Disadvantages: self fertilization leads to homozygosity and reducesd variation.
Viola (common pansy), oxalis, and Commelina produce two types of flower chasmogamous- above
ground and Cleistogamous- below ground / surface of ground.
Groundnut – also shows geocarpy with cleistgamy just as in commelina
Garden pea – self pollinated due to keel enclosing stamen and stigma
Bisexual flower plant : Auto, G, X
Monoecious plant: G, X – No auto
Dioecious plant: X - No auto, Geitono
Out breeding devices / adaption’s for cross pollination
Most flower are bisexual, so to prevent continous self pollination which leads to reduced variation
Heterozygosity increases- variation
Examples: Sunflowers, Maize, Millets, cotton, coconut, fruit and vegetables
5
1. Unisexual flower – monoecious / doecious plants.
2. Dichogamy : anther and stigma mature at different times. Or the pollen release ad stigma
receptivity is not synchonised
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a) Protandry ; anther mature first
b) Protogny : stigma mature first
3. Herkogamy : flower is bisexual – cross pollinated. The anther and stigma are placed at different
postion so that the pollen cannot come in contact with stigma of the same flower.
4. Self – incompatibility / instraspecific incompatibility / self sterility : this is a genetic mechanism
and prevent self pollen (from the same flower or other flower of the same plant ) from fertilizing
the ovules by inhibiting pollen germination or pollen tube growth in the pistil.
 Gamettophytic SI : If the incompatibility is due to genotype of pollen
 Sporophytic SI : if the incompatibility is due to genotype of pollen
 Mechanism – prevention of pollen germination, retardation of growth, deorientation of
pollen tube, or even failure of nuclear fusion.
 It is controlled by genes with multiple alleles
Agents of cross pollination / pollinators :
Abiotic agents:
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Wind (common) and water.
Wind is more common
Wind and water pollinated plants do not have colorful flower, nectar. Fragrance.
Reason : no evolutionary benefits (colour and fragrance – attract biotic pollinators)
Pollen coming in contact with stigma is a chance factor, so large number of pollen produced as
compared to ovules available, to compensate for uncertainities and loss of pollen.
A. Anemophily : Pollination by wind
 The polen here are smooth, light, non sticky, dry and small.
 Versatile anther – free movement of anther o filament
 Feathery stigma – [grasses] to trap air borne pollen
 Style is very long band comes out of flower, just like the corn Cob in which the silk / tassel is
the style and stigma which wave in the wind to trap pollen
 Numerous flower packed into acompact inflorescence with well exposed stamens and also
stigma
 Flower are with single ovule / ovary (grasses)
 Mostly the anemophilous plants are monocious or dioecious.
 Ex., Grasses (Sorghum, Maize), Coconut – hay fever eg. Papaya, Gate, Mulbery, Cannabis.
Wheat and rice are self pollinated but show all wind pollination adaptations
B. Hydophily : Pollination by water.
It is rare – 30 genera (mainly monocots)
In most water pollinated plants pollen covered by mucilage to prevent wetting
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Also exine is absent in many of them (no need of protection from dryness)
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C. Epihydrophily : pollination occur on the surface of water. Eg., submerged hydrophyte Vallisneria
(ribbon weed). In Vallisneria, the female flower reach the surface of water by the long stalk and
the male flower or pollen grains are released on the surface of water. They are carried passively
by water currents: some of them eventually reach the female flower and the stigma
D. Hypohydrophily : pollination occur inside water: e.g. Zostera, Hydrilla Zostera / Sea grasses.
Ceratophllum In marine sea grass / Zostera marine female flower remain submerged in water
and the filamentous pollen grains are released inside the water polen grains in many such species
are long, ribbon like and they are carried passively inside the water; some of them reach the
stigma and achieve pollination.
Nymphaea / water lily, Nelumbo and Water Hyacinth / Eichhornia the pollination is by insect or wind as
their flower emerges above the level of water.
Biotic agents: majority of plants use biotic agents
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Insects: Bees (most dominant biotic pollinator), Butterflies, Moths, Flies, Beetles, Wasps, Ants
Birds (sun birds and humming birds), Bats
Snails,
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Large animals
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Primates like lemurs,
Arboreal rodents,
Reptiles like Gecko lizards, snake
Flower of animal pollinated plants are adapted for a particular species of animal
A. Entomophily : Pollination by insects.
 Flowers are colorful, lrge sized, scented, rich in nectar
 If flower are small, then all clustered into a conspicuous colorful big inflorescence – sunflower
 Nectar and pollen are the rewards for sustained animal visits
 When animal visit flower for reward, they come in contact with anther and stigma. The pollen is
sticky (due to pollenkit) and rough so the body of insect get coated with the polen and it
transfers tom stigma of other flower whixh is large, rough, sticky.
 Flies and beetles pollinated flower secrete foul odours
 Moth pollinated flower (night blooming) have white petals, scented and have nectary
Other floral rewards
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Providing safe places to lay eggs; the tallest flower of Amorphophallus (the flower itself is about
6 feet in height).
Close association: the Pronuba moth (Tageticula) is associated with Yucca, the insect and plant
cannot complete the life cycle without each other. The moth deposits its eggs in the locule of
the ovary and the flower, in turn, gets pollinated by the moth. The larvae of the moth come out
of the eggs as the seeds starts developing.
Blastophaga : wasp is symbiotically associated with fig for the pollination – inflorescence used
for eggs laying, larva offered seeds
Pollen / nectar robbers: Take the reward – donot pollinate
No reward: The Mediterranean orchid Ophrys muscifera does not provide reward to the
pollinator; instead it employs ‘sexual deciet’ to get pollination done by a bee. One petal of its
flower resembles the female of the bee in size, colour and markings. The male tree is attracted
to the flower as it mistakes it to be a female and it pseudocopulates the flower.
Some other cases of insect pollination
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8
Aristolochia shows pit fall / fly trap mechanism.
Salvia shows turn pipe / lever mechanism for pollination
Calotropis and orchids shows translator shows translator mechanism,
Fabaceae -Piston mechanism – insect attracted by standard, it sits on wings and preses the keel
down finally stigma and anther comes out and brushes on the abdomen of insect.
B. Zoophily : pollination by animals
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C. Ornithophily: Polination vy birds. Bright colour, no scent, good nectar eg. Erythrina / Coral
tree,Bombax / Read silk cotton tree, Calistemon / bottle brush, Butea monosperma, Tobacco,
Bignonia,Banana
D. Chiropterophily: pollination by bats. Flower is white, odourless. Less number of prominent
stamens present like Adansonia / baobab tree has 1500-2000 stamens; large quantities of polen
are produced eg. Kigelia pinnata (Sausage tree), Adansonia, Anthocephalus (kadamb), Bauhinia
megalandra . Agave – century plant, Banana
E. Malacophily: Pollination by snail and slug
F. Ophiophily: Pollination by snakes
G. Myophily: Pollination by files
H. Mellitophily: Pollination by honey bees
I. Myrmecophily: Pollination by ants seen in Rubiaceae family, Mango (Bees, ants and other
insects).
The Pollinators in
1.
2.
3.
4.
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6.
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8.
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10.
11.
12.
13.
14.
15.
Cucumber : Bees
Mango : Bees
Coriander : Bees
Lobia : Bees
Onion : Bees
Cotton : Bees
Rose : Bees
Lemon : Bees
Banana : Bee, Wasp, Birds, bats
Tobacco : Moth, Birds
Eucalyptus : Insects
Papaya - wind
Peepal : wasp
Morus alba : wind
Asteraceae, Labiatae – Bees, Butterflies
The Pistils, Megasporangium (ovule) and Embryo sac
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Pistil / carpel / gynoecium: megasporophyll
Syncarpous- Papaver
Apaorarpous-Michelia.
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Stigma [receive polen], Style and Ovary
Placenta-megasporangia / integumented indehiscent megasporangia / ovule
One ovule – Wheat, Paddy, Mango
Many ovule – Papaya, Water melon, Orchids (millons), Poppy, Orobanche and striga
Ovule structure (Megasporangia)
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Ovule is attached to placenta
Funicle: The stalk of avule
Hilum: Point of attachment between the ovule and funicle.
Raphe: Is also the part of funicle fused with the ovule.
Integuments: each ovule ha sone / two protective covering around the ovule
Aril: It is a collar like outgrowth from the base of ovule sometimes considered as 3rd integument,
e.g., Litchi (Edible fleshy aril), Myristica / Jaiphal (dearilled seed is spice), lnga edulis
Micropyle:
o Micropyle helps in the entry of PT into the ovule
o Micropyle in the seed helps in the entry of water and oxygen in the seed
Caruncle / strophiole: It is a spongy outgrowth of integuments / hilum near the micropyle in
castor
Chalaza: the basal part of ovule opposite to the micropyle
Nucellus: megasporangia / parenchymatous tissue in ovule-abundant reserve food in its cells.
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
Embryo sac / female gametophyte: single ES inside the nucellus of ovule
Types of ovule
1. Orthotropous / atropus ovule : MCHF all in a straight line
2. Anatropous / Reasuoinate ovule: Inverted ovule, 180 degree inversion, MP and funicle side by
side and MP Faces placenta, Funicle fused with ovule 82 % angio
3. Hemitropous : 90 degree bend
4. Campylotropous: 90 degree bend but MP sirected down e.g. Leguminosae – Pisum sativum,
Cruciferae- Capsella
5. Amphitropous: Ovule curved / bends from middle and Es become horse shoe shaped
6. Circinotropous: 360 degree bend e.g. Cactus,
Megasporogenesis: development of megaspore from MMC by meiosis
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1
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Inside nucellus single MMc / Megasporocyte develop towards the micropyle, it is a large cell
with dense cytoplasm and prominent nucleus. [it develop from 1 Archesporial initial]
MMC divide by meiosis to from a linear tetrad of megaspore , but only the 4th megaspore from
their micropyle survives which is the larger cell [ Chalazal end] .
P.Mahshwari classified embryo sac into 3 types,
o Monosporic ES : In a majority of flowering plants, one the megaspore is functional while the
other three degenerate. Functional megaspore develops into the female gametophyte
(embryo ac). This method of embryo sac formation from a single megaspore is termed
monosporic development
o Bisporic ES:
o Tetrasporic ES: All the four nucleus after meiosis survive. Then ES is formed
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Development of Monosporic Embryo Sac / Megametophyte / Megagametogenesis
 Surviving megaspore nucleus – three free nuclear mitosis[2,4 and finally 8 nucleate
structure formed –(4 nucleus at each pole)
 Six of the eight nuclei are surrounded by cell walls and organized into cells; the
remaining two nuclei, called polar nuclei are situated below are formed
 Polygonum type of Embryo sac / typical Es at maturity has :7 cell and 8 nucleus
Structures in an Embryo sacSynergids, Egg, Antipodals, Polar nuclei
2
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Egg apparatus towards micropylar end – three cells are grouped together at the
micropylar end and constitute the egg apparatus. The egg apparatus in turn, consists of
two synergids and one egg cell.
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Synergid :
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Degenerating and persisting synergid
The PT enters into degenerating synergid
The synegids have special cellular thickenings at the micropylar tip called filiform
apparatus,
FA guides and attracts pollen tube
FA –Ca-B-inositol-sugae compolex which attracts the PT
Obturator guides the pollen tube towards micropyle
Egg / Oosphere- it is the haploid female gamete
Antipodals- 3 haloid cell towards chalazal end
Just before fertilization, 2 polar nuclei – fuse to form 2n secondary nucleus. All cells are haloid in
the embryo sac except the secondary nucleus / Central cell.
Central cell: Largest cell in embryo sac, contains two polar nuclei, it is the precursor of
endosperm
In a mature unfertilized ovule there are two generations
In a fertilized ovule / seed there arethree generations=2n is the egg / zygote, embryo, 3n is the
endosperm and 2n is the integument, nucellus
Pollen-pistil interaction:
Events-from pollen deposition on the stigma until pollen tubes enter the ovule- are together
referred to as pollen-pistil interaction.
It involves rejecting wrong type and guiding right type of pollen compatibility of pollen is
decided by chemical components of the pollen interacting with those of the pistil.
If the pollen landed on stigma is on of the wrong type, the pistil rejects the pollen by preventing
pollen germination on the stigma or the pollen tube growth in the style.
Right pollen:
Compatible pollen germinates on the stigma to produce a pollen tube through one of the germ
pores. The content of the pollen grain move into the pollen tube. Pollen tube grows through the
tissues of the stigma and style and reaches the ovary.
3
In plants which shed pollen at 2 celled, the generative cell divided and froms the two male
gametes during growth of pollen tube in the stigma.
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In plant which shed pollen in the three celled condition, pollen tubes carry the two male
gametes from the beginning.
Pollen tube, after reaching the ovary, enters the ovule through the micropyle and then enters
one of the synergids through the filiform apparatus
The PT shows chemottopic movement. Shows tip growth; release IAA, cell wall of PT is made up
of pectin and cellulose
Many recent studies have shown that filiform apparatus present at the micropylar part of the
synergids guides the entry of pollen tube.
The plant breeder can also manipulate pollen-pistil interaction, even in compatible pollination,
to get desired hybrids
Entry of PT into the ovule
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Porogamy is the entry thru Micropyle
Misogamy is the entry thru integuments like Cucumber / Cucurbits
Chalazogamy is the entry thru chalaza – Casuarina [2nd pref Basigamy]
Artificial hybridization:
Emasculation: If the female parent bears bisexual flower, removal of anthers from the flower
bud before the anther dehisces. No need of emasculation in sexual flowers.
Bagging: Emasculated flowers are covered by butter paper bag, to prevent contamination of its
stigma with unwanted pollen.
Pollination: When the stigma of bagged flower attains receptively, mature pollen grains
collected from anther of the male parent are dusted on the stigma, and the flower are
rebagged, and the fruits allowed to develop.
Pollen germination:
if pollen from Pea, Chickpea, Crotalaria, Balsam and Vinca is kept in 10% sugar soln-after 15-30
min PT will be seen unde low power lens of C.M
when pollen lands on the stigma, it germinates and forms polen tube this is called 2 celled
pollen forms 3 celled inside style/ forerunner/precursor of male gamete-Generative
cell/Microspore/MMC
Entry into the ES
4
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PT enters deg. Synergid thru FA
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Fertilisation
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Syngamy / generative fertilization:gg (oosphere) fuses with male gamete – zygote.
Amphimixis is union of a male and female gamete in sexual reproduction,
Vegetative fertilization / triple fusion: Central cell (2PN / Secondary Nucleus) fuses with
male gamete-PEC / PEN [3n]
DF is Syngamy + TF within the same embryo sac from 2 male gametes of same PT
DF is an exclusive / unique character of angiosperm only
DF absent in Orchidaceae, Podostmonaceae-no endosperm.
DF was discovered by Nawaschin in Fritillaria and Lilium
Df product – endosperm / seed
3 gamte, 4 cell nd 5 nucleus involved in DF
Heterofertilisation
Post-fertilisation Events in Sexual Reproduction
Events in sexual reproduction after the formation of zygote are called post-fertilisation events.
The Zygote
Formation of the diploid zygote is universal in all sexually reproducing organisms. In organisms with
external fertilisation, zygote is formed in the external medium (usually water), whereas in those
exhibiting internal fertilisation, zygote is formed inside the body of the organism.
Further development of the zygote depends on the type of life cycle the organism has and the
environment it is exposed to. In organisms belonging to fungi and algae, zygote develops a thick wall
that is resistant to dessication and damage. It undergoes a period of rest before germination. In
organisms with haplontic life cycle, zygote divides by meiosis to form haploid spores that grow into
haploid individuals.
Zygote is the vital link that ensures continuity of species between organisms of one generation and the
next. Every sexually reproducing organism, including human beings begin life as a single cell–the zygote.
Embryogenesis
Embryogenesis refers to the process of development of embryo from the zygote. During
embryogenesis, zygote undergoes cell division (mitosis) and cell differentiation. While cell divisions
increase the number of cells in the developing embryo; cell differentiation helps groups of cells to
undergo certain modifications to form specialised tissues and organs to form an organism.
Animals are categorised into oviparous and viviparous based on whether the development of the
zygote take place outside the body of the female parent or inside, i.e., whether they lay
5
fertilised/unfertilised eggs or give birth to young ones. In oviparous animals like reptiles and birds, the
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fertilised eggs covered by hard calcareous shell are laid in a safe place in the environment; after a period
of incubation young ones hatch out. On the other hand, in viviparous animals (majority of mammals
including human beings), the zygote develops into a young one inside the body of the female organism.
After attaining a certain stage of growth, the young ones are delivered out of the body of the female
organism. Because of proper embryonic care and protection, the chances of survival of young ones is
greater in viviparous organisms.
In flowering plants, the zygote is formed inside the ovule. After fertilisation the sepals, petals and
stamens of the flower wither and fall off. Can you name a plant in which the sepals remain
attached? The pistil however, remains attached to the plant. The zygote develops into the embryo and
the ovules develop into the seed. The ovary develops into the fruit which develops a thick wall called
pericarp that is protective in function (Figure 8). After dispersal, seeds germinate under favourable
conditions to produce new plants.
Endosperm
After entering one of the synergids, the pollen tube releases the two male gametes into the cytoplasm
of the synergid. One of the male gametes moves towards the egg cell and fuses with its nucleus thus
completing the syngamy. This results in the formation of a diploid cell, the zygote. The other male
gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce a
triploid primary endosperm nucleus (PEN) (Figure 13a). As this involves the fusion of three haploid
nuclei it is termed triple fusion. Since two types of fusions, syngamy and triple fusion take place in an
embryo sac the phenomenon is termed double fertilisation, an event unique to flowering plants. The
central cell after triple fusion becomes the primary endosperm cell (PEC) and develops into
6
the endosperm while the zygote develops into an embryo.
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Embryogeny
Embryo develops at the micropylar end of the embryo sac where the zygote is situated. Most zygotes
divide only after certain amount of endosperm is formed. This is an adaptation to provide assured
nutrition to the developing embryo. Though the seeds differ greatly, the early stages of embryo
development (embryogeny) are similar in both monocotyledons and dicotyledons. Figure 13 depicts the
stages of embryogeny in a dicotyledonous embryo. The zygote gives rise to the proembryo and
subsequently to the globular, heart-shaped and mature embryo.
A typical dicotyledonous embryo (Figure 14a), consists of an embryonal axis and two cotyledons. The
portion of embryonal axis above the level of cotyledons is the epicotyl, which terminates with
the plumule or stem tip. The cylindrical portion below the level of cotyledons is hypocotyl that
7
terminates at its lower end in the radical or root tip. The root tip is covered with a root cap.
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Embryos of monocotyledons (Figure 14 b) possess only one cotyledon. In the grass family the cotyledon
is called scutellum that is situated towards one side (lateral) of the embryonal axis. At its lower end, the
embryonal axis has the radical and root cap enclosed in an undifferentiated sheath
called coleorrhiza. The portion of the embryonal axis above the level of attachment of scutellum is the
epicotyl. Epicotyl has a shoot apex and a few leaf primordia enclosed in a hollow foliar structure,
the coleoptile.
Soak a few seeds in water (say of wheat, maize, peas, chickpeas, ground nut) overnight. Then split the
seeds and observe the various parts of the embryo and the seed.
Seeds
In angiosperms, the seed is the final product of sexual reproduction. It is often described as a fertilised
ovule. Seeds are formed inside fruits. A seed typically consists of seed coat(s), cotyledon(s) and an
embryo axis. The cotyledons of the embryo are simple structures, generally thick and swollen due to
storage of food reserves (as in legumes). Mature seeds may be non-albuminous or albuminous. Nonalbuminous seeds have no residual endosperm as it is completely consumed during embryo
development (e.g., pea, groundnut). Albuminous seeds retain a part of endosperm as it is not
completely used up during embryo development (e.g., wheat, maize, barley, castor, sunflower).
Occasionally, in some seeds such as black pepper and beet, remnants of nucellus are also persistent.
This residual, persistent nucellus is the perisperm.
Integuments of ovules harden as tough protective seed coats (Figure 15a). The micropyle remains as a
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small pore in the seed coat. This facilitates entry of oxygen and water into the seed during germination.
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As the seed matures, its water content is reduced and seeds become relatively dry (10-15 per cent
moisture by mass). The general metabolic activity of the embryo slows down. The embryo may enter a
state of inactivity called dormancy, or if favorable conditions are available (adequate moisture, oxygen
and suitable temperature), they germinate.
As ovules mature into seeds, the ovary develops into a fruit, i.e., the transformation of ovules into seeds
and ovary into fruit proceeds simultaneously. The wall of the ovary develops into the wall of fruit
called pericarp. The fruits may be fleshy as in guava, orange, mango, etc., or may be dry, as in
groundnut, and mustard, etc. Many fruits have evolved mechanisms for dispersal of seeds. Recall the
classification of fruits and their dispersal mechanisms that you have studied in an earlier class.Is there
any relationship between number of ovules in an ovary and the number of seeds present in a fruit?
In most plants, by the time the fruit develops from the ovary, other floral parts degenerate and fall off.
However, in a few species such as apple, strawberry, cashew, etc., the thalamus also contributes to fruit
formation. Such fruits are called false fruits (Figure 15b). Most fruits however develop only from the
ovary and are called true fruits. Although in most of the species, fruits are the results of fertilisation,
there are a few species in which fruits develop without fertilisation. Such fruits are
called parthenocarpic fruits. Banana is one such example. Parthenocarpy can be induced through the
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application of growth hormones and such fruits are seedless.
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Seeds offer several advantages to angiosperms. Firstly, since reproductive processes such as pollination
and fertilisation are independent of water, seed formation is more dependable. Also seeds have better
adaptive strategies for dispersal to new habitats and help the species to colonise in other areas. As they
have sufficient food reserves, young seedlings are nourished until they are capable of photosynthesis on
their own. The hard seed coat provides protection to the young embryo. Being products of sexual
0
reproduction, they generate new genetic combinations leading to variations.
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Seed is the basis of our agriculture. Dehydration and dormancy of mature seeds are crucial for storage
of seeds which can be used as food throughout the year and also to raise crop in the next season. Can
you imagine agriculture in the absence of seeds, or in the presence of seeds which germinate straight
away soon after formation and cannot be stored?
How long do the seeds remain alive after they are dispersed? This period again varies greatly. In a few
species the seeds lose viability within a few months. Seeds of a large number of species live for several
years. Some seeds can remain alive for hundreds of years. There are several records of very old yet
viable seeds. The oldest is that of a lupine, Lupinus arcticus excavated from Arctic Tundra. The seed
germinated and flowered after an estimated record of 10,000 years of dormancy. A recent record of
2000 years old viable seed is of the date palm, Phoenix dactylifera discovered during the archeological
excavation at King Herod’s palace near the Dead Sea.
Apomixis
Although seeds, in general are the products of fertilisation, a few flowering plants such as some species
of Asteraceae and grasses, have evolved a special mechanism, to produce seeds without fertilisation,
called apomixis. What is fruit production without fertilisation called? Thus, apomixis is a form of asexual
reproduction that mimics sexual reproduction. There are several ways of development of apomictic
seeds. In some species, the diploid egg cell is formed without reduction division and develops into the
embryo without fertilisation. More often, as in many Citrus and Mango varieties some of the nucellar
cells surrounding the embryo sac start dividing, protrude into the embryo sac and develop into the
embryos. In such species each ovule contains many embryos. Occurrence of more than one embryo in a
seed is referred as polyembryony.
Types of apomixes- explanation by flow chart
1. Gametophytic agamospermy: Embryo develop from diploid egg cell of diploid embryo ac. Such
embryo sac is formed without meiosis. It is of two types
a) Diplospory : The diploid embryo sac is formed from MMC without meiosis later on diploid
parthenogenis occur e.g taraxacum
b) Apospory : The diploid ES is formed from nucellus / integuments without meiosis, later on
diploid parthenogensis occur E
2. Sporophytic apomixes / agamospermy / Adventive embryony / Sporophytic budding: The cells
of nucellus / integuments surrounding ES starts dividing and protrude into the ES and develop
ino embryos directly without forming any diploid ES OR Formation of embryo directly from
nucellus / integuments
1
Nuclear embryo is apomictic diploid
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This result result in Polyembryony : Formation of more than one embryo in one seed.
Discovered by Leeuwenhoek in citrus
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Squeezing seed of orange will release many embryos
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E.g.,Citrus [Nucellar embryos], Mango, Opuntia.
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Parthenogenesis : Embryo develop from haploid or diploid egg without fertilization /
development of egg without fertilization
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Pseudogamy / gynogenesis :Like parthenogenesis but require stimulation by male gamete,here
pollination occurs but no syngamy
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Apogamy : Development of haploid embryo / from a cell of gametephyte like suspensor,
antipodal other than egg without fertilization
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Development of sporophyte fron from gameteophyte without fusion of gametes is Apogamy
Advantage of Apomictic seeds
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One of the problems of hybrids is that have to be produced every year. If the seeds collected
from hybrids sown, the plants in the progeny will segregate and do not maintain hybrids are
characters. Production of hybrid seeds is costly and hence the cost of hybrid seeds becomes too
expensive for the farmers. If these hybrids are made into apomicts, there is no segregation of
characters in the hybrid progeny. Then the farmers can be keep on using the hybrid seeds to
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raise new crop year after year and the does not have to buy hybrid seeds every year.
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