In simple words, germination can be defined as the growth of a seed into a young plant or a seedling.
What is Seed Germination?
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 seed germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm.
Also, read: Formation and Dispersal of Seeds
The Process of Seed Germination
The complete process of seed germination is carried out in the following steps:
- 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 seed germination.
- 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 seed germination, the cell of the seeds become metabolically active, elongate and divide to give rise to the seedling.
Also Read Parts of a Seed.
Conditions Necessary for Seed Germination
Here are some important requirements which are essential for a seed to germinate into a seedling and to a plant.
Water: It is extremely necessary for the germination of seeds. Some seeds are extremely dry and need to take a considerable amount of water, relative to the dry weight of the seed. Water plays an important role in seed germination. It helps by providing necessary hydration for the vital activities of protoplasm, provides dissolved oxygen for the growing embryo, softens the seed coats and increases the seed permeability. It also helps in the rupturing of seed and also converts the insoluble food into soluble form for its translocation to the embryo.
Oxygen: It is an important and essential source of energy required for seed growth. It is required by the germinating seed for the metabolism and is used as a part of aerobic respiration until it manages to grow green leaves of its own. Oxygen can be found in the pores of soil particles, but if the seed is buried too deep it will be deprived of this oxygen.
Temperature: For a seed to germinate, it requires a moderate temperature of around 25-30°C. Quite obviously different seeds require different optimum temperatures. There are some seeds which require special requirements either lower or higher temperature between 5 to 40°C.
Light or darkness: This can act as an environmental trigger. Many seeds do not germinate until sunlight falls on them.
The process of seed germination triggers under the above mentioned favourable conditions. The seeds undergo rapid expansion and growth of the embryo and subsequently rupturing the covering layers and emergence of the radicle. This radicle emergence is considered the completion of germination.
Explore more: Significance of Seeds and Fruits Formation
Factors Affecting Seed Germination
There are some major factors that affect seed germination. These include:
- Water: The poor or additional supply of water affects the seed germination.
- 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 seed germination.
In certain cases, a temperature below the moderate level slows down the seed 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 seed germination.
- Some seeds require more time for their germination.
To learn more about the seed, its parts, seed germination, its process, factors affecting seed germinations and any other related topics visit BYJU’S Biology