post fertilization changes

POST FERTILIZATION CHANGES

DEVELOPMENT OF ENDOSPERM

Endosperm is the nutr it ive t issue for nourishment of developed embryo.

In some angiosperm, the product of second fert i l izat ion or tr ip le fusion is PEN.

I t develops into endosperm.

In some cases i t is absent such seeds are cal led non endospermic or ex-albuminous seeds eg. pea, bean, grams etc.

In other angiosperm, endosperm persists in mature seeds and i t support the growth of embryo, such seeds are cal led endospermic or a lbuminous seeds eg. Sunfl ower, castor, coconut, maize etc

DEPEND ON THE MODE OF DEVELOPMENT

Endosperm

Nuclear endoperm

Cellular endosperm

Helobial endosper

m

TYPE OF ENDOSPERM

DEVELOPMENT OF EMBRYO

FORMATION OF SEEDS AND FRUITS Simaltaneously with the development of embryo and

endosperm, ovary enlarges in size.

Sepals, petals, stamens, style and stigma fall off and ovary changes into fruit.

Ovary wall change into pericarp (fruit wall).

Pericarp initially is green and on ripening become orange, red, purple, yellow etc.

Each ovule in ovary also enlarge, outer integument become thick and hard outer seed coat, called testa .

Inner integument become thin, inner seed coat, called tegmen.

PARTHENOCARPY

Mostly, the fruits are formed after fertilization but there are some species in which fruits develop without fertilization.

This is called parthenocarpy and such fruits are called parthenocarpic fruits eg. Banana.

APOMIXIS AND POLYEMBRYONY

Seeds are the product of fertilization.

In some spices of grasses seeds are produce without fertilization.

This is called apomixis and such seed is called apomictic seeds.

Some nucellar cell near embryo sac start dividing and develop many embryo this is called polyembryony.

SIGNIFICANCE OF SEED

The distribution and dominance of angiosperms on earth is due to the seeds.

Success of seeds as propogule is due to many characters such as –

1. Dormancy 2. Viability3. Reserve food4. Protective coat 5. Dispersal 6. Edible fruits