Causes of Dormancy

1. Seed coat factors

a. Seed coat impermeable to water

• Common in seeds of leguminaceae, malvaceae, convolvulaceae and chenopodiaceae
• Seed coat with thick waxy cuticle, lignin and suberin barriers makes seeds impermeable to water

b. Seed coat impermeable to oxygen

• Any disturbances to the entry of oxygen and exit of CO2 decreases respiration and there by remains in dormant condition

c. Mechanically resistant seed coat

• Hard seed coats of nuts make it difficult for embryo to germinate and break the seed coat
• High salt concentration in water also aids to cause mechanical resistance to germination

2. Embryo factors

a. Immature/rudimentary embryo

• Found in Ranunculus spp.
• These embryos require after ripening though their growth is completed morphologically
• This is also called physiological dormancy

3. Inhibitory Factors

• The inhibitors (e.g : coumarin, caffeic acid, ferulic acid and ABA) may present in the embryo, endosperm or seed coat or pericarp
• These inhibitors deactivate enzymes like Amylase, protease and phytase
• This will limit the supply of simple substances like sugars and fatty acids
• If the ratio of these inhibitors is higher than the that of endogenous hormones especially GA the seeds remain dormant till a balance between them is reached in favor of growth promoters.