Photoperiodism, Vernalisation, And Seed Dormancy – Definition, Meaning, Stages, Importance, Facts

Introduction

Plant growth and development is a continuous stream of complicated processes that start from the time of germination, proceed through maturity, and end with plant reproduction. It controls the phases of growth and the transitions between them that are impelled by internal genetic programs and external environmental cues.

An understanding of photoperiodism, vernalization, and seed dormancy is important in making a plant aligned to its seasonal environment: flowering and hence reproduction occur at the most appropriate time to maximize reproductive success, while plants survive periods of unfavourable conditions. In this way, such mechanisms will turn out to be very instrumental in manipulating agricultural practices toward better crop yields and hence food security and sustainable agriculture.

Photoperiodism

Photoperiodism is discussed below:

Definition

Photoperiodism is an organism's physiological response to the duration of day or night, mainly in plants. It is the duration of illumination that affects several developmental procedures like flowering. This is because plants do measure light duration to know the time for reproduction and growth.

Types of Photoperiodic Responses

The types of plants photoperiodic responses are:

Short-day plants

Short-day plants, for example, poinsettias or chrysanthemums, bloom when the day length is shorter than a critical length.

Long-day plants

Long-day plants, including spinach and radishes, need longer daylight periods to be induced to flower.

Day-neutral plants

Day-neutral plants, examples include tomatoes and cucumbers, their flowering does not depend on day length. It can flower in any light condition.

Vernalisation

Vernalisation is discussed below:

Definition

Vernalization is a process wherein plants require some period of cold temperature before they initiate flowering. This cold exposure ensures that the flowering procedure is timed appropriately during the spring season and not during the winter period.

Examples of Vernalisation

Winter wheat and other biennials, such as carrots or beets, need periods of cold to break dormancy so they may flower the next season.

Agricultural Applications

Vernalisation is used in agriculture to

• Ensure early flowering and harvesting by artificial cold treatment of seeds.

• Useful for synchronizing crop cycles and increasing yield in temperate regions.

• Useful during winters, especially in temperate climates, this aids in ensuring flowering and fruiting at the correct time.

Seed Dormancy

Seed dormancy is discussed below:

Definition

Seed dormancy is the period when seeds fail to germinate even when the environment is very conducive to their growth. It is considered to be of different kinds: intrinsic due to genetic programs, enforced due to environmental factors, and induced due to exogenous factors.

Types of Seed Dormancy

The types of seed dormancy are:

Breaking Seed Dormancy

Stratification, scarification, other techniques of cold, and physical or chemical treatments in breaking dormancy support germination. These methods allow control of seed germination in an agricultural environment to establish crops successfully.

Ecological and Evolutionary Significance

Seed dormancy is a very vital attribute to plant survival since avoiding germination at the most inappropriate time of the year, makes a coincidence in time so that seeds germinate at the right time. It avails evolutionary advantages since it is tailored for various environmental situations.

Interconnections between Photoperiodism, Vernalisation, and Seed Dormancy

These processes interact to coordinate the life cycles of plants concerning growth, flowering, and seed germination at appropriate times for the environment. Photoperiodism and vernalisation interact in flowering and growth, and mechanisms of seed dormancy ensure that seeds survive until the conditions are appropriate for germination. All together, they help plants adapt to seasonality and environmental variables.

Photoperiodism, Vernalisation, and Seed Dormancy NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Key points about Photoperiodism, Vernalisation and Seed Dormancy

• Interconnectedness between the three

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

Recommended video on "Photoperiodism, Vernalisation, And Seed Dormancy"