Factors that causes the seed dormancy?

Question

What are the factors that causes the seed dormancy?
Or
Mechanisms that maintain seed dormancy.

Answer 1

The main factors that causes the seed dormancy are:

1. Seed coats impermeable to water: The seed of certain family have very hard seed coats which are impermeable to water. This dormancy remains until the testa layer decay by soil microorganisms. The impermeable seed coats are found in the family leguminosae, Malvaceae, convolvulaceae.
2. Seed coat impermeable to oxygen:  This type of dormancy is because of the impermeability of the seed coats to oxygen. But later seeds become more permeable to oxygen so that it germinates afterwards. This type of dormancy in found in the family compositae.
3. Mechanically resistant seed coat: In certain seeds of weeds have hard seed coats that prevent the expansion of embryo.
4. Immaturity of the embryo: In the seeds of plants like the Orchids, Ginkgo etc. The immaturity of the embryo is due to the failure of the embryo to develop when the seeds are shed.
5. Due to the effect of germination inhibitors: The inhibition caused due to the presence of the inhibitor substances in the seed coat, endosperm, embryo or any structure. Some of the important germination inhibitors are; Coumarin, Phythalids, Ferulic acid, Abscisic acid, Dehydracetic acid and parasorbic acid.
6. Low temperature: In certain plants the seeds remain dormant after harvest because they require low temperature for germination. The seeds germinate in the spring season.
7. Light sensitive seeds: In certain seed the germination is affected by the light so the absence of light results in the seed dormancy. These seeds which are sensitive to sunlight are termed as the photoblastic seeds, where as in some other seeds the light inhibits the seed germination so they are negatively photoblastic.