Seed Germination: Description, Process, Diagram, Stages, Necessity, And Its Major Factors

What Is Seed Germination?

Seed germination may be defined as the fundamental process by which different species of plants develop from one seed into a plant. This process influences crop yield along with its quality. A common instance of seed germination could be the sprouting of a seedling from a seed of an angiosperm or gymnosperm.

Process Of Seed Germination

The whole process of seed germination occurs in some of the following significant steps:

Imbibition

At optimum temperature, the seeds quickly initiate absorption of water, causing swelling and softening of the seed coat. This stage of seed germination is known as imbibition. It reinitiates growth through the activation of enzymes, respiration of the seed, synthesis of proteins, and metabolism of stored food. Hence, it is usually regarded as a lag phase of seed germination.

Emergence Of Radicle And Plumule

As the seed coat ruptures, a radicle, or primary root, emerges, and the seed can start taking up underground water. Following radicle development, the plumule, or shoot, grows upward and forms the seedling.

Seedling Development

In the last stage of seed germination, the cells of the seed become metabolically active. Through cell elongation and cell division, the seedling forms in the final stage of germination.

Conditions Required For Seed Germination

For the germination of a seed into a seedling, and later a plant, the following are some of the key conditions that need to be fulfilled:

Water

Water is essential for seed germination. Exceedingly dry seeds have to imbibe a fairly significant amount of water about their dry weight. Water performs the roles of hydrating vital activities, loosening seed coats, enhancing permeability, and converting insoluble food into a soluble form for transport to the embryo.

Oxygen

Oxygen is a critical source of energy for seed growth. Metabolism requires it, and it is used in aerobic respiration until such time as the seedling has developed green leaves and can photosynthesize. Oxygen, however, can be found in the pores of soil particles and is absent in seeds buried too deep.

Temperature

Seeds germinate best at temperatures between 25 to 30°C, although the optimum temperature conditions vary with the seeds. Some may require higher or lower temperatures than this.

Light/Darkness

Light is also an environmental cue by which germination is triggered. While some seeds will not germinate until they are in the light, others need darkness to trigger the event.

Under these perfect conditions, seed germination is initiated, in which the embryo starts to expand and develop rapidly, breaking out with the radicle. The emergence of the radicle marks the completion of germination.

Factors Affecting Seed Germination

Seed germination is influenced by several factors that can mainly be categorized into external and internal factors.

External Factors

1. Water: Both the absence of water and excess water supply may inhibit seed germination.

2. Temperature: Temperature influences the speed of germination as well as metabolic activity within the seed. Temperature that is either very high or very low may retard germination or even promote the growth of fungi.

3. Oxygen: Oxygen is needed for respiration by the developing seeds. The absence of oxygen prevents germination.

Internal Factors

1. Seed Dormancy: Seed dormancy refers to a situation whereby the seed fails to germinate even when environmental conditions are favourable.

2. Seed Coat Resistance: Water and gas impermeable seed coats inhibit the amount of water that is taken up and oxygen exchange.

3. Immature Embryo: Seeds having underdeveloped or immature embryos won't be able to germinate.

4. Plant Growth Regulators: Some seeds possess growth inhibitors which act against germination.

5. Time Requirement: Various seeds simply take longer to germinate.

Difference Between Seed Germination and Dormancy

The difference between seed germination and seed dormancy is given in the table below:

Seed Germination NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Process of Seed germination

• COnditions required for seed germination

Practice Questions for NEET

Q1. The reasons of seed dormancy include

1. Impermeable and hard seed coat

2. Presence of chemical inhibitors such as abscisic acids, phenolic acids, para-ascorbic acid

3. Immature embryos

4. All of the above

Correct answer: 4) All of the above

Explanation:

Reasons for Seed Dormancy:
Seed dormancy can occur due to several factors, including:

1. Impermeable and Hard Seed Coat: A tough seed coat prevents water and oxygen from reaching the embryo, delaying germination.

2. Presence of Chemical Inhibitors: Compounds like abscisic acid, phenolic acids, and para-ascorbic acid inhibit germination by suppressing enzymatic activities.

3. Immature Embryos: Seeds with underdeveloped embryos require additional time for maturation before they can germinate.

These mechanisms help seeds survive unfavourable environmental conditions and germinate when conditions are optimal.

Hence, the correct answer is option 4) All of the above.

Q2. Which one is not a cause of seed dormancy ?

1. ABA

2. Seed coat

3. Optimum temperature

4. Gibberellins

Correct answer: 4) Gibberellins

Explanation:

• A- Seed coat is hard and impermeable and prevents the entry of water and oxygen

• B- ABA is a chemical growth inhibitor

• At the time of dispersal, some seeds are structurally immature and the embryo is unable to synthesise gibberellic acid

• D- Gibberellic acid does not act as an inhibitor to control seed dormancy.

Hence, the correct answer is option 4) gibberellins.

Q3. To overcome seed dormancy, the effect of inhibitory substances can be removed by subjecting the seeds to

1. Chilling temperature

2. Application of auxin

3. Application of gibberellins

4. Both a and c

Correct answer: 4) Both a and c

Explanation:

Chilling the seeds or administering specific chemicals, such as gibberellic acid and nitrates, eliminates the effect of inhibitory substances present in seeds. Inhibitors, which cause dormancy, present in the seed coat can be neutralized with these treatments so that germination can be effectively achieved. There are other techniques like water soaking to leach out inhibitors, hot water treatments, and mechanical scarification for enhancing moisture uptake and encouraging seed growth.

Hence the correct answer is Option (4) Both a and c.

Also Read:

• MCQs on Seed Dormancy

• Functions of Ethylene

• Auxin Bioassay