Seed dormancy is important for plant survival.

It ensures that seed will germinate only under

optimal light, temperature, and moisture.

Aleurone Endosperm

Scutellum(cotyledon)

Radicle

Seed dormancy also gives additional time for seed dispersal over distances.

ABA is the main reason for seed dormancy

GAABA

(ABA)

ABA inhibits seed germination. Actually, it is the ratio of ABA to GA in

seeds determines whether the seed remains dormant

or germinates.

Mutants cannot synthesize or

perceive (sense) ABA will have seeds that

germinates right after seed maturation

(precocious germination).

GAABAABAABA

Light, cold or water (rain) trigger the

inactivation of ABA, which

makes dormant

seeds able to germinate.

GA

After seeds take up water, GA is released from the embryo to signal aleurone.

-amylase

The aleurone responds by synthesizing and secreting digestive enzymes (-amylase) to

hydrolyze stored nutrients in the endosperm.

Nutrients (ex. sugars) absorbed from the endosperm by the scutellum (cotyledon) are

consumed by the seedling during germination.

The growth of seedling starting with the roots first, then shoot growth follows.