Seed germination may be defined as the fundamental process by which different plant species grow from a single seed into a plant. This process influences both crop yield and quality. A common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm.
Stages of Seed Germination
- During the beginning stage of the germination, the seeds take up water rapidly and this results in swelling and softening of the seed coat at an optimum temperature. This stage is referred to as an Imbibition. It starts the growth process by activation of enzymes. The seed activates its internal physiology and starts to respire and produce proteins and metabolizes the stored food. This is a lag phase of the germination of seed.
- By rupturing of the seed coat, radicle emerges to form a primary root. The seed starts absorbing underground water. After the emerging of the radicle and the plumule, shoot starts growing upwards.
- In the final stage of germination, the cell of the seeds become metabolically active, elongate and divide to give rise to the seedling.
Factors Affecting Germination of Seed
There are some major factors that affect germination of seeds. These include:
- Water: The poor or additional supply of water affects the germination of seed.
- Temperature: This affects the growth rate as well as the metabolism of the seed.
- Oxygen: Germinating seeds respire vigorously and release the energy required for their growth. Therefore, deficiency of oxygen affects the germination.
In certain cases, a temperature below the moderate level slows down the germination and promotes fungal growth. In some cases, the germination stops at the temperature above the moderate level.
This is a condition in which the seeds are prevented from germinating even under favourable conditions.
During seed dormancy:
- The seed coat, which is resistant to water and gases, restrict water-uptake and oxygen exchange.
- The seeds with undeveloped or immature embryo do not germinate.
- Certain seeds contain plant growth regulators, which inhibit germination.
- Some seeds require more time for their germination.