POST-FERTILISATION :

STRUCTURES AND EVENTSDasari. Sreekanth. M.Sc., NET, TS/AP-

SET, (Ph.D).Department of Botany,

Osmania University,Hyderabd.

Email id: shreekanthdasari@gmail.com

POST-FERTILISATION : STRUCTURES AND EVENTS

PEN Endosperm (3n)Egg Zygote (2n) EmbryoOvule seedOvary Friuit.

Coconut water: free-nuclear endosperm

White kernel: cellular endosperm

Endosperm DevelopmentPEN

Free nuclear divisions

cell wall formation

Cellular endosperm

Embryo Development

EmbryoDicot embryo Monocot embryo

The Seed

Fertilised ovuleNon-Albuminous or Albuminous

Perisperm: persistent nucellus

Seed Dormancy

The Seed

Seed formation

Endospermic & Non-EndospermicMonocots & Dicots

Seed Formation• The zygote grows

repeatedly by mitosis to form an embryo

• An embryo consists of a plumule (future shoot), a radical (future root) and cotyledons (food stores needed for germination)

3N endosperm nucleus

2N Zygote

Endospermic Seed Formation

• The endosperm nucleus (3N) divides repeatedly to form the endosperm in endospermic seeds. This endosperm acts as a food store for the developing seed

• e.g. maize

3N endosperm nucleus

2N Zygote

Non endospermic Seed Formation

In non-endospermic seeds the endosperm is used up in the early stages of seed development so the food is stored in the cotyledons

e.g. bean 3N endosperm nucleus

2N Zygote

EndospermFood store for developing embryo

EmbryoPlumule, radicle, cotyledons

Integuments, becomes the seed coat

Seed Formation

If all the endosperm is absorbed by the developing embryo the seed is a non endospermic seed e.g. broad bean

Non endospermic Seed Formation

If all the endosperm is not absorbed by the developing embryo the seed is an endospermic seed e.g. Maize

Endospermic Seed Formation

Seed types and structure

Seed

embryo

Plumule (immature shoot)

Radicle (immature root)

Cotyledon (food supply or seed leaf)

endosperm Food store

All seeds

In some seeds

Endosperm

Seed coat (testa)

Cotyledon

Plumule – will develop into a new shoot

Radicle – will develop into a new root

Endospermic Seed e.g. Maize

Seed coat (testa)

Cotyledon

Plumule

Radicle

Non-Endospermic seed e.g. Broad Bean

e.g. Broad Bean e.g. Maize

Plumule

Radicle

Cotyledon

Endosperm

Non–endospermic and Endospermic seed

Development of the seed and fruit

Dicot embryos develop two cotyledons

Monocot embryos develop a single cotyledon

Fig. 38.8

micropyle –opening in ovule where pollen tube attached, sperm entered

hilum –scar where ovule attached to ovary

radicle –embryonic root

Seedling

Part of the Seed Function

Embryo Whole dormant immature plant inside the seed

Radicle Part of the embryo which will become the roots of the plant after germination

Plumule Part of the embryo which will become the shoots (stems, leaves etc.) of the plant after germination

Cotyledon This is a “leaf” of the embryo which can • be a food reserve (in non-endospermous seeds) or • absorb nutrients from the endosperm for growth of the during germination (in endospermous seeds)

Testa Protective coating of the seed, formed from the integuments of the ovule.

Functions of the Parts of the Seeds

more dependabledispersal to new habitatssufficient food reservesThe hard seed coat: ProtectionVariations

Seed: Advantages

Fruit Formation

Fruit Formation The ovule becomes the seed The ovary becomes the fruit

Fruit FormationA fruit is a mature

ovary that may contain seeds

The process of fruit formation is stimulated by growth regulators produced by the seeds

Seedless FruitsCan be formed in two ways1. Genetically Either naturally or by

special breeding programmes

e.g. seedless oranges

Seedless Fruits2. Growth regulators e.g.

Auxins

If large amounts of growth regulators are sprayed on flowers fruits may form without fertilisation

e.g. seedless grapes

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How do seedless fruits form?1. May be a genetic variety and occur

naturally e.g. some bananas & cucumbers.2. Spray flowers with auxin or gibberellin

(growth regulators) and fruits form without fertilisation taking place.

3. Gibberellin may also cause bigger fruit to form.

4. Ethene is used to ripen fruit and de-green skins of oranges, lemons and grapefruit.

Fleshy fruit/Dry fruit Fruit wall- Pericarp Pericarp- Epicarp, Endocarp, Mesocarp False fruits/True fruits Parthenocarpic fruits: developed without

fertilisation

Fruits

Seed development without fertilisation

Diploid egg Embryo

Nucellar cells protrude into the embryo sac and develop into the embryosPolyembryony

Apomixis

POLYEMBYONY:- It is the phenomenon of formation of more than one embryo during the development of seed. Rao(1965) has found polyembryony to develop during seed germination in vandal caused by cleavage of apical promeristem of single embryo.

Polyembryony was discovered by Leeuwenhoek(1719) in case of citrus .

Polyembryony is of three types I] Simple- eg. Poa , Casuarinas, Citrus II] Cleavage polyembryony- eg. Pinus, orchids III] Adventitive polyembryony-eg. Citrus,

opuntia ,Onion, Mangifera, Trillium,Groundnut.

The end POST-FERTILISATION : STRUCTURES

AND EVENTS