1. Seed dormancy is important for plant survival
Seed dormancy is important for plant survival. It ensures that seed will germinate only under optimal light, temperature, and moisture.
Aleurone
Endosperm
Scutellum
(cotyledon)
Seed dormancy also gives additional time for seed dispersal over distances.
Radicle

2. ABA is the main reason for seed dormancy
ABA inhibits seed germination. Actually, it is the ratio of ABA to GA in seeds determines whether the seed remains dormant or germinates.
ABA GA
(ABA)

3. Mutants cannot synthesize or perceive (sense) ABA will have seeds that germinates right after seed maturation (precocious germination).

4. Light, cold or water (rain) trigger the inactivation of ABA, which makes dormant seeds able to germinate.
ABA
ABA
ABA GA

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

6. The aleurone responds by synthesizing and secreting digestive enzymes (a-amylase) to hydrolyze stored nutrients in the endosperm.
a-amylase

7. Nutrients (ex. sugars) absorbed from the endosperm by the scutellum (cotyledon) are consumed by the seedling during germination.

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