Give various causes for seed dormancy.

Various Causes for Seed Dormancy :

Underdeveloped embryo.

Seed coats impermeable to water.

Mechanically hard and strong seed coats which do not permit germination.

Physiologically immature embryo.

Presence of some germination-inhibiting chemicals. Amongst them the main one is Abscisic acid.

Amongst hormones, Gibberrelins are absent in dormant seeds.

At this time, ABA remains active.

It inhibits the transcription of genes. As a result, proper enzymes are not synthesized.

Removal of Seed Dormancy :

When production of Gibberellins begins in the seed and when their concentration exceeds that of $A B A$, the effect of $\mathrm{ABA}$ is removed and the embryo becomes active.

To induce germination of seed, it is necessary to remove its dormancy.

Such a removal of dormancy can also be artificially achieved.

Some of these methods are as under -

Seeds can be scraped lightly with sandpaper. Thus, their seed coats become permeable to water and germination is induced.

A similar result can be achieved by using chemicals.

Soaked seeds in an $\mathrm{O}_{2}$ containing environment, can be provided higher or lower temperature for a definite period. Dormancy is removed in this way.