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Vernalisation: History, Site, Requirements, Mechanism, Types of Plants on the Basis of Lifespan , Significance of Vrnalisation, Practice Problems and FAQs

Vernalisation: History, Site, Requirements, Mechanism, Types of Plants on the Basis of Lifespan , Significance of Vrnalisation, Practice Problems and FAQs

You can see a variety of plants around you. You may be growing a variety of flowering plants in your garden too. We all like flowers. You know that in your garden plants flower at different times. For example, Dahlia plants bloom in winter. 


Fig: Dahlia flowers

But have you ever wondered why there are some plants that bloom twice a year whereas some plants that bloom once a year? 

Different plants have different requirements for blooming. Some important factors for the blooming of flowers include weather conditions, pollinating agents, precipitation or rainfall, sunlight, etc. Hence, plants bloom at that time of the year when they get the required conditions for their blooming. But it will be nice if we are able to make them bloom whenever we need. Do you think this is possible? Yes, it is possible because science has reached that level now. So in this article let's take a deep dive into the details of vernalisation, one of the such treatment methods for the plants. 

List of contents

Vernalisation

Vernalisation is the process of shortening of the juvenile or vegetative phase and fastening flowering by a previous cold treatment. Vernalisation promotes the plant to achieve proper vegetative growth and allows it to prepare to bloom. It ensures proper development of leaves, stem and the vascular system. It prevents premature development of the reproductive system. It enables the plant to have sufficient time to reach maturity.


GIF: Vernalisation allows proper vegetative growth in plants

Seasons

The rotation of Earth around the Sun and the tilt of its axis causes variations on Earth. It causes annual variations in the intensity and duration of sunlight or solar radiation and temperature reaching on Earth. It results in distinct seasons on Earth. 


Fig: Reason for the formation of seasons

A season is a period of the year that is distinguished by special climatic conditions. These seasons follow one another regularly and each season has its own light, temperature, and weather patterns. The following are the four seasons:

  • Spring
  • Summer
  • Autumn
  • Winter


Fig: Seasons

History of vernalisation

Many plants such as biennials do not flower if they are not exposed to low temperatures. They normally show vegetative growth during the warm season. After receiving the low temperature during winter they grow faster and bear flowers and fruits. This was first noticed by Klippart in 1857. 

In 1928, Lysenko proposed that winter varieties of biennials can be made to flower in one season by providing low temperature treatment. This can be achieved by providing low temperature treatment to the water soaked seeds. He discovered vernalisation. 

Site of vernalisation

The sites of vernalisation in a plant are normally the meristematic cells present on the shoot tips, root tips, developing leaves, tips of embryos etc. They are continuously dividing cells.


GIF: Shoot apical meristem

Requirements of vernalisation

The process of vernalisation requires the following factors: 

Duration of low temperature

The duration of low temperature treatment varies. It depends on the plant species. 

Actively dividing cells

The site of vernalisation in plants is actively dividing cells. Hence the treatment is normally done on germinating seeds or meristematic tissues.


Fig: Meristematic tissue

Low temperature

The low temperature required for the vernalisation process varies from 0 - 4 °C. It depends on the plant species.

Water

Plants will receive the vernalisation treatment and show its effect, if the humidity is maintained properly. Hence watering the plants is highly important. 

Gases

Plants require a proper amount of oxygen to perform the various life processes. They also require carbon dioxide for photosynthesis. This is hence highly important for successful vernalization. 

Nutrients

The chemical substances that provide nourishment to the living organisms are termed as nutrients. Different minerals are required in different amounts in the plant body.


Fig: Requirements of a plant

Process of vernalisation

The following steps are commonly followed in vernalisation process:

  • Select the seeds.
  • Soak them in water to allow germination.
  • Expose them to 0 - 4 °C for a few weeks.
  • Then sow to the ground. 

Mechanism of vernalisation

The vernalisation stimulus is normally received by the actively dividing cells present on the shoot tips, developing leaves and embryonic tips. From here it is translocated to all parts of the plant. This stimulus is commonly called vernalin. It is believed that gibberellins also show the same effect of vernalin.

Types of plants based on lifespan

On the basis of lifespan plants are of of three types as follows:

  • Annual plants
  • Biennial plants
  • Perennial plants


Fig: Types of plants on the basis of duration of flowering pattern

Annual plants

Annual plants are those which germinate, grow, and bloom in one year. They show their entire life cycle from the seed to flower and to seed in a single growing season. The roots, leaves and stems of the plant die annually. Here the seed which is in dormant stage connects one generation to the next generation. Examples include wheat, barley and rye. 

Varieties of annual plants

Some annual plants, such as wheat, barley, and rye have two varieties: 

  • Spring varieties
  • Winter varieties

Spring variety

The plants of spring varieties are planted in spring. They grow over spring and some parts of summer. They are harvested in mid summer. They do not require any exposure to a cold environment to produce flowers.


Fig: Annual plant of spring variety

Winter variety

The plants of winter varieties are planted in autumn. These plants grow into small seedlings in winter. They continue their growth in spring. In mid-summer, they flower and produce grains. They are harvested in mid-summer. They need to undergo the winter cold temperatures to produce flowers next summer. This phenomenon is known as vernalisation. If these plants are sown in the spring season, they would not produce flowers.


Fig: Annual plant of winter variety

Biennial plants

The word biennial is derived from two words, ‘bi’ means two and ‘annus’ means years. These are monocarpic plants that grow and flower over two years. They take two years normally to complete their life cycle. In the first season, the growth normally results in a small cluster (rosette) of leaves near to the soil surface. In the second season growth results in elongation of the stem, flowering and formation of seed. This is followed by the death of the entire plant. Examples include sugar beet and cabbage.


Fig: Examples of biennial plants

Vernalisation in biennials

The biennial plants are grown in spring. They germinate in spring and undergo vegetative growth in summer. They enter a period of dormancy once they reach winter. In the second year, the plants flower in spring. They form seed during summer and die in winter. The key is the exposure to cold in winter, and this shows vernalisation in biennials.


Fig: Biennial plant

Subjecting the growth of a biennial plant to a cold treatment stimulates a subsequent photoperiodic flowering response. This speeds up the process of flowering in biennials. 


Fig: Vernalisation in biennials

Perennial plants

Perennial plants are characterised as those plants that live for more than two years. The winter varieties show vernalisation in them. Generally in these plants, the top portion of the plant dies back each winter and regrows in the following spring from the same root system. Examples include purple coneflower. Many perennial plants keep their leaves around the year and offer attractive groundcover and borders.

Significance of vernalisation

The following are the few importance of vernalisation in plants:

  • It helps in shortening the period between germination and flowering.
  • It increases yield as more than one crop can be obtained during a year.
  • Sowing of winter crops in the spring season after this treatment helps the plants to escape from the severe winter.
  • It increases resistance to cold in plants. 
  • It helps in removing the kernel wrinkles in Triticale, a product obtained from crossing wheat (Triticum) and rye (Secale)

Practice Problems

Q1. Match column I (Plant variety) with column II (Growing method) and select the correct option from below.

Column I (Plant variety)

Column II (Growing method)

A. Winter variety

  1. Planted in spring, grows till winter, flowers and forms seeds in the next year

B. Spring variety

2. Planted in autumn, germinates in 

winter, grows in spring, and 

harvested usually during mid-summer

C. Biennial variety

3. Planted in spring and 

harvested during mid-summer

A. A - 2, B - 3, C - 1
B. A - 3, B - 2, C - 1
C. A - 1, B - 3, C - 2
D. A - 1, B - 2, C - 3

Solution: The plants of winter varieties are planted in autumn. These plants grow into small seedlings in winter. They continue their growth in spring. In mid-summer, they flower and produce grain. They are harvested in mid-summer. The plants of spring varieties are planted in spring. They grow over spring and some parts of summer. They are harvested in mid summer. The biennial plants are grown in spring. They germinate in spring and undergo vegetative growth in summer. They enter a period of dormancy once they reach winter. In the second year, the plants flower in spring. Hence, the correct option is a.

Q2. Find the odd one out

A. Coconut tree
B. Bamboo
C. Rice
D. Wheat

Solution: Monocarpic plants flower once in their lifetime. Examples include wheat, rice, and bamboo. Polycarpic plants produce flowers and seeds every year. Examples include coconut trees. Hence, the correct option is a.

Q3. Which hormone is responsible for the phenomenon of vernalisation?
Answer: Gibberellin is primarily involved in the phenomenon of vernalisation. This is because it is a key hormone that stimulates plant development and bud formation.

Q4. Which are the sites of vernalisation?
Answer: Vernalisation is the process of shortening of the juvenile or vegetative phase and fastening flowering by a previous cold treatment. Vernalisation promotes the plant to achieve proper vegetative growth and allows it to prepare to bloom. It occurs in the apical meristems of shoots, developing leaves and germinating seeds.

Q5. What is the significance of vernalisation?
Answer: Vernalisation promotes the plant to achieve proper vegetative growth. It ensures proper development of leaves, stem and the vascular system. It prevents premature development of the reproductive system. It enables the plant to have sufficient time to reach maturity.

Q6. Who discovered the phenomenon of vernalisation in plants?
Answer: Lysenko discovered vernalisation in plants in the year 1928. He was a Russian scientist.

FAQs

Question 1. What is the main difference between vernalisation and photoperiodism?
Answer: Vernalisation is a phenomenon due to which flowering depends either quantitatively or qualitatively on the exposure to a low temperature. It is the process of shortening of the juvenile or vegetative phase and fastening flowering by a previous cold treatment.Vernalisation promotes the plant to achieve proper vegetative growth. On the other hand, photoperiodism is the phenomenon of the response of plants to the relative length of day and night.

Question 2. What is called seed vernalisation?
Answer: In seed vernalisation the moistened seeds are subjected to cold temperatures to stimulate germination. This method is used when plant growers need to plant seed in the spring season. Vernalisation method imitates winter conditions and causes seed germination.

Question 3. Give an example for a plant which does not show vernalisation?
Answer: Natural varieties of rice plants normally do not show vernalisation. 

Question 4. Why is vernalisation important in agriculture?
Answer: Vernalisation is important in agriculture. Some plant species bloom in cold regions and these plant species need vernalisation to enter the regenerative stage. It induces the early flowering and the fruit set in plants. This is useful in increasing the yield and quality. More than one crop can be obtained during a year using this method.

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