Vernalization is the process by which flowering is promoted through a period of cold temperature exposure. It involves the perception of cold, which results in the formation of a floral hormone called vernalin. Vernalization requires specific conditions like the age of the plant, duration and temperature of cold exposure, oxygen, sugar, and water. There are two main theories that explain its mechanism - the phasic development theory which proposes vernalization accelerates a developmental phase, and the hormonal theory which suggests it converts a precursor into the flowering hormone vernalin. Vernalization is significant for crop improvement by converting winter varieties to spring varieties and inducing early flowering.

1. Vernalization

2. Vernalization
• Latin word vernus = of the spring
• It is the process by which flowering is promoted with cold
temperature( chilling treatment)
• The term vernalization was introduced by Lysenko
• The low temperature requirement for flowering was first noticed by
Klippart
• The low temperature is given to buds, seeds or seedlings

3. The potential sites of vernalization are apical meristems, actively
dividing cells and fragments of embryo
It is believed that the perception of cold stimulus results in the
formation of a floral hormone (vernalin), which is transmitted to
different parts of the plant
But this hormone has not yet been isolated

4. • The effect of vernalization can be cancelled by high temperature
treatment immediately after it and the phenomenon is called
devernalization
• Studies have shown that gibberellins can replace the low
temperature requirement for vernalization
• So it is assumed that the product of vernalization, which induces
flowering could be a gibberellin or mixture of gibberellins

5. Conditions necessary for vernalization
1) Age of the plant
• It is a major factor influencing vernalization and varies in
different species
• Germinating seeds and developing embryo can be subjected to
vernalization in cereals
• In henbane, vernalization is found to be successful only after the
plant has reached rosette stage and has completed atleast 10
days of growth

6. 2) Low temperature treatment and its duration
• The optimum temperature for vernalization is 0 to 50C
• But it varies in different species of plants
• In the plant winter rye, vernalization fails below -40C and is effective
up to 140C
• The duration of treatment also varies with a minimum of 4 days and a
maximum of three months

7. 3) Oxygen
Vernalization will not take place in the absence of oxygen and so it is
an aerobic process utilizing metabolic energy
4) Sugar
During embryo cultures, vernalization without sugar in the media is
ineffective
5) Water
For vernalization, water is essential. Vernalization of dry seeds is not
possible. Seeds must imbibe minimum 50 % of water for vernalization

8. Mechanism of vernalization
There are two main theories to explain the mechanism of vernalization
a) Phasic Development theory
• It was proposed by Lysenko
• The development of a seed plant consists of a series of phases, which
proceeds in a definite sequence
• A phase cannot start until the previous phase is completed
• These phases need external conditions for completion
• Thermophase and photophase are involved in plant development
• Vernalization accelerates the thermophase, after which the photophase
starts
• Vernalization can be done in pea, rice, soyabean, barley, oats etc

9. b) Hormonal theory
• It was first proposed by Lang and Melchers
• According to this theory, vernalization involves the formation of
the flowering hormone vernalin
The concept can be explained as follows:-
A precursor A is converted into a thermolabile compound B by cold
treatment. Under normal temperature, B changes into a stable product
C (vernalin), which is responsible for flowering. At high temperature, B
will be converted to D and flowering does not take place

10. Significance of vernalization
• Winter varieties can be converted to spring varieties
• Crop improvement
• Induce early flowering
• Increases cold resistance of plants
• Increases resistance of plants to fungal diseases