Student Projects/Germination of seeds

SEED GERMINATION

Germination is defined as the growth of a seed into a young plant or a seedling. It can also be defined as the fundamental process by which plants grow from a single seed. An example of seed germination is the sprouting of a seedling from a seed of a monocot or dicot plant.

The Process of Seed Germination:

Seed germination takes place in the following steps:

• The seeds absorb water, which results in the swelling of the seed and radicle and plumule comes out due to the rupture of seed coat. This process is called imbibition.

• Respiration: due the entering of water in the seed, it is rehydrated causing the resumption of metabolic activities. Initially their respiration may be anaerobic later it becomes anaerobic as oxygen starts entering the seed. This is lag phase of seed germination.

• In the next stage, the cell of the seed elongates and divides, which brings out the roots out of the seed and cotyledons expand, which are the true leaves of the plant.

Conditions Necessary for Seed Germination

• Water is extremely necessary for the germination of seeds. Dry seeds need to take water, relative to their dry weight. Water helps in 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.

• Oxygen: It is an essential source of energy required for seed growth. It is required for the metabolism. Oxygen can be found in-between sand particles.

• Temperature: Seed requires a moderate temperature of around 25-30°C for germination. Different seeds require different optimum temperatures. Some seeds require special requirements either lower or higher temperature between 5 to 40°C.

• Light: It acts as an environmental trigger. Many seeds do not germinate until sunlight falls on them.

Factors Affecting Seed Germination

External factors

1. Water: The seed germination is affected by poor or additional supply of water.

2. Temperature: It affects the growth rate and the metabolism of the seed.

3. Oxygen: As the germinating seeds respire vigorously and release the energy required for their growth, deficiency of oxygen affects the seed germination

Internal Factors

Seed Dormancy

Sometimes, the seeds are prevented from germinating even under favourable conditions. The seeds are said to be dormant in such cases. During seed dormancy, • The seed coat becomes resistant to water and gases which restrict water uptake and oxygen exchange.

• seeds may have undeveloped or immature embryo which do not germinate.

• Some seeds contain plant growth regulators that inhibit germination.

• Some seeds take more time to start germinating.