Question

The causes of seed dormancy are
A. Impermeable seed coats
B. Presence of seed inhibitory substances
C. Presence of ABA
D. All of the above

Answer 1

Seed dormancy can be defined as a physiological inability of a seed to germinate even under favorable conditions.

Complete answer: The main causes of seed dormancy are as follows:
1. Hard Seed Coat or impermeable seed coats: Hard seed coat stops the entry of water into the seed. A hard coat blocks the exchange of gases, especially oxygen. Oxygen is necessary for respiration. Hard seed coats cause mechanical resistance which influences radicles not to come out which causes dormancy.
2. Immature Embryo: The embryo is fully developed inside the seed before shedding it from the parent plants. In Fraxinus and Anemone development of the embryo is incomplete at the dispersal stage – for such seeds remain dormant and fail to germinate.
3. Presence of ABA (Abscisic acid): ABA is considered as a chief phytohormone regulating seed dormancy.
4. Presence of seed inhibitory substances: There are several naturally occurring compounds that inhibit the germination of seeds such as phenolic compounds.
The example of phenolic compounds is ferulic acid, parasorbic acid, and coumarin.
These compounds are present in the embryo or in the seed coats and inhibit the germination of the seed.

Hence, the correct answer is option D. all of the above.

Note: Some other causes of seed dormancy are light, temperature, and the time period after-ripening of fruit.