Part 5: Plant reproduction
3. Seed dormancy
Normally when environmental conditions are favourable, a seed will begin to germinate, but in some cases a seed remains dormant even though the conditions are perfect for germination.
Why? To delay germination.
Why? To cause germination to be staggered, which allows seeds to travel different distances before they germinate, ensuring a wide geographical spread and so that seeds germinate at different times, protecting some of the seedlings against short periods of inclement weather or passing herbivores.
Some seeds can germinate after more than 2000 years of dormancy!
Primary dormancy: Seeds are released from the plant in a dormant state.
Secondary dormancy: Seeds are not dormant when they are released from the plant but become dormant if environmental conditions are unfavourable.
There are two types of seed dormancy
Coat imposed dormancy
- Prevention of water uptake
- Mechanical constraint
- Interference with gas exchange
- Retention of inhibitors
- Inhibitor production.
Embryo dormancy
- Embryo inhibits germination through the presence of growth inhibitors and the lack of growth promoters