Vernalization is the process where some plant species require a period of cold temperatures to induce flowering. It is most effective between 1-7°C. There are two main theories that explain the mechanisms of vernalization - the phase development theory and hormone theory. The phase development theory states that low temperatures accelerate the completion of the thermo phase to induce early flowering. The hormone theory suggests that low temperatures produce a flowering stimulus called vernalin, which interacts with gibberellins and florigen to induce flowering under correct photoperiod conditions. Vernalization is most effective at specific developmental stages of the plant and can be reversed by high temperatures through a process called devernalization.

1. Vernalization
R. Sivakumar
Lecture 24
06.01.2023
Low temperature

2. Some crop plants require prior treatment followed by
appropriate photoperiod for flowering
Term coined by Lysenko
Induction of flowering by low temperature treatment
Vernalization - Definition

3. 1. Prepares the plant to flowering
2. Most effective temperature is 1 to 7°C
3. Vernalization alone cannot induce flowering
5. Vernalization stimulus called as Vernalin
Important points about vernalization
4. After vernalization - correct photoperiod

4. 2. Plant - Active apical meristem
Perception of stimulus for flower initiation
1. Seed - Embryo is the most receptive tissue
Site of Vernalization
Actively dividing cells of leaves and roots

5. Soak the seeds in water Keep it in 1 to 7°C
Correct duration
Dry the seeds in shade
Sow the seeds to field
Vernalization in seed – Technique

6. Conditions for Vernalization
1. Age of the plant
Cereals - Germinating seeds & developing embryos
2. Low Temperature - 1 to 7°C - Most effective
3. Duration of treatment - Mostly 1½ months
Vernalization effective only certain stage of crop
Four days to three months
Several months needed for vernalization
Over vernalization

7. 4. Oxygen - Important for Vernalization
Absence of O2 - Vernalizationis not effective
5. Water - Essential for Vernalization
Vernalization - Aerobic process
It is not possible in dry seeds

8. Mechanisms of Vernalization
Theories of Vernalization
1. Phase Development Theory - Lysenko Theory
2. Hormone Theory 1. Chailakhyan Hypothesis
2. Lang and Melchars

9. Phase development theory
1. Growth and development are two distinct phenomena
2. Development of a plant consists - series of phases
3. Next phase initiates only on the termination of
previous phase
4. Completion of phase depends upon
light and temperature

10. 5. Two Phases
Thermo Phase Photo phase
Temperature dependent Light dependent
Ex: Winter wheat variety
Low temperature is required for completion of thermo phase
Vernalization accelerates thermo phase - Induces early flowering
Photoperiodism

11. Hormone theory - Chailakhyan
Low Temperature treatment
Flowering stimulus
Vernalin
Gibberellins
Flowering in LD plants
Anthesin
Florigen

12. Gibberellins are ineffective to produce flowers in
SD plants
Vernalin
No florigen No flowering
No Anthesin
SD plants lack Anthesin
Because
Gibberellin

13. A B C Florigen
Flowering
Low tem Normal tem Correct photoperiod
Degradation of B
De Vernalization
High Tem
D No flowering
Hormone Theory -- Lang and Melchars
Vernalin

15. Devernalization
Effect of vernalization can be removed by
high temperature treatment
This reverse effect is called De vernalization
It occurs at more than 30°C

16. Low temperature
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