Introduction:  Vernalization is the process whereby flowering is promoted by a cold treatment given to a fully hydrated seed or to a growing plant.  Dry seeds do not respond to the cold treatment.  Due to vernalization, the vegetative period of the plant is cut short resulting in an early flowering.  Also called yarovization.  Without the cold treatment, plants that require vernalization show delayed flowering or remain vegetative.  In many cases, these plants grow as rosettes with no elongation of the stem. History:  Klippart,1857- first noticed the low-temperature requirement for flowering while working with winter wheat and spring wheat.  Lysenko,1938-used the term vernalization for a low-temperature promotion of flowering in plants.  Chourad ,1960- defined vernaliZation as “acquisition or acceleration of the ability to flower by a chilling treatment”. Vernalization  For vernalization the seeds are allowed to germinate for some time and then are given cold treatment from 0 ̊C to 5 ̊C.  The period of cold treatment, varies from few days to many weeks.  After the cold treatment the seedlings are allowed to dry for some time and then sown.  Vernalization prepares the plant for flowering.  The cold stimulus usually perceived by the apical meristems. But in some species, all dividing cells of roots and leaves may be the potential sites of vernalization eg. Leennario biennis.  Vernalization induces the plant to produce a hormone called vernalin. It was discovered by Melcher(1936).  The vernalization stimulus can be transmitted from one plant to another through grafting.  The age of the plant is an important factor in determining the responsiveness of the plant to the cold stimulus and it differs in different species.  The suitable temperatures for vernalization ranges between 1 to 6 ̊c.  At higher temperature from 7 ̊c onwards response of the plant is decreased.  A temperature of about 12 to 14 ̊c is most ineffective in vernalizing the plant.  The vernalization is an aerobic process and requires metabolic energy.  In the absence of oxygen cold treatment becomes completely inefficient.  A sufficient amount of water is also essential.  Vernalization of dry seeds is not possible. Factors affecting Vernalization: Site of vernalization Age of plants Appropriate low temperature Duration of exposure Mechanism of vernalization: Two theories.. 1. Phasic development theory 2. Hormonal theories. Epigenetic Changes in Gene Expression:  Vernalization May Involve Epigenetic Changes in Gene Expression.  Changes in gene expression that are stable even after the signal that induced the change (in this case cold) is removed are known as epigenetic regulation.  One model for how vernalization affects flowering is that there are stable changes in the pattern of gene expression in the meristem after cold treatment.  The involvement of epigenetic regulation in the vernalization process has been confirmed in the LDP Arabidopsis.

1. VERNALIZATION IN PLANTS
PRESENTED BY : NUSRAT SHEIKH

2. Content
 Introduction to vernalization
 History
 Vernalization
 Factors affecting vernalization
 Mechanism of vernalization
 Devernalization
 Practical applications
 Reference

3. Introduction
 Vernalization is the process whereby flowering is promoted by a cold
treatment given to a fully hydrated seed or to a growing plant.
 Dry seeds do not respond to the cold treatment.
 Due to vernalization, the vegetative period of the plant is cut short
resulting in an early flowering.
 Also called yarovization.
 Without the cold treatment, plants that require vernalization show delayed
flowering or remain vegetative.
 In many cases, these plants grow as rosettes with no elongation of the
stem.

4. History
 Klippart,1857- first noticed the low-temperature requirement for flowering
while working with winter wheat and spring wheat.
 Lysenko,1938-used the term vernalization for a low-temperature promotion of
flowering in plants.
 Chourad ,1960- defined vernaliZation as “acquisition or acceleration of the
ability to flower by a chilling treatment”.

5. Vernalization
 For vernalization the seeds are allowed to germinate for some time and then
are given cold treatment from 0 ̊C to 5 ̊C.
 The period of cold treatment, varies from few days to many weeks.
 After the cold treatment the seedlings are allowed to dry for some time and
then sown.
 Vernalization prepares the plant for flowering.
 The cold stimulus usually perceived by the apical meristems. But in some
species, all dividing cells of roots and leaves may be the potential sites of
vernalization eg. Leennario biennis.

6.  Vernalization induces the plant to produce a hormone called vernalin. It was
discovered by Melcher(1936).
 The vernalization stimulus can be transmitted from one plant to another
through grafting.
 The age of the plant is an important factor in determining the responsiveness of
the plant to the cold stimulus and it differs in different species.
 The suitable temperatures for vernalization ranges between 1 to 6 ̊c.
 At higher temperature from 7 ̊c onwards response of the plant is decreased.
 A temperature of about 12 to 14 ̊c is most ineffective in vernalizing the plant.

7.  The vernalization is an aerobic process and requires metabolic energy.
 In the absence of oxygen cold treatment becomes completely inefficient.
 A sufficient amount of water is also essential.
 Vernalization of dry seeds is not possible.

8. Factors affecting Vernalization
Site of vernalization
 Metabolic active apical meristem is the site of temperature perception for
flower initiation.
 Younger leaves are more susceptible to vernalization.
Age of plants
 It is an important factor in determining the responsiveness of the plant to the
cold stimulus and it differ in different species.
 In cereals like winter wheat, vernalization best occur in germinating seeds
and even at an embryonic stage in the mother plant

9. Appropriate low temperature
 Suitable temperatures for vernalizing the plants range between 1- 6⁰C .
 The effectiveness of the low temp decreases from 0 to -4⁰C and at about -
6⁰C is completely ineffective.
 Similarly, at higher temp from 7⁰C onwards the response of the plant
decreases and, at about 12 - 14⁰C are almost ineffective.
Duration of exposure
 Besides an appropriate low temp, a suitable duration of this cold treatment
is essential for vernalization.
 It differs in different species.
 Usually, the duration of the chilling treatment is about one and a half
months or more

10. Mechanism of vernalization
Two theories..
1. Phasic development theory
2. Hormonal theories.

11. Phasic development theory
 Proposed by Lysenko in 1934.
 According to this theory there is a series of phases in the development of a
plant.
 Each phase is stimulated by an environmental factor such as temperature, light,
etc.
 Commencement of one phase will take place only after the completion of the
proceeding phase.
 There are two phases
1.Thermophase
2.Photophase
 Thermophase depends on temperature.Vernalization accelerates thermophile.
 Thermophase should be followed by photophase which requires light.

12. Hormonal theories
 Melcher (1939)
 He proposed that chilling treatment induces the formation of a new
floral hormone called vernalin.
 This hormone is transmitted to other parts of the plant.
 He grafted a vernalized plant with an unvernalized plant.
 The unvernalized plant also initiates flowering.
 The hormone,vrnalin diffuses from the vernalized plant to the
unvernalized plant and induces flowering.

13. Epigenetic Changes in Gene Expression
 Vernalization May Involve Epigenetic Changes in Gene Expression.
 Changes in gene expression that are stable even after the signal that induced the
change (in this case cold) is removed are known as epigenetic regulation.
 One model for how vernalization affects flowering is that there are stable changes
in the pattern of gene expression in the meristem after cold treatment.
 The involvement of epigenetic regulation in the vernalization process has been
confirmed in the LDP Arabidopsis.

14. ‣A gene that acts as a repressor of flowering has been identified: FLOWERING
LOCUS C (FLC). FLC is highly expressed in non-vernalized shoot apical meristems
(Michaels and Amasino 2000).
‣ After vernalization, this gene is epigenetically switched off by an unknown
mechanism for the remainder of the plant’s life cycle.

15. Devernalization
 The reversion of vernalization by high-temperature treatment is called
devernalization.
 Devernalization is effected by treating the vernalized seeds or buds with
high temperature.
 Lang et al (1957) demonstrated that application of gibberellin can replace
the cold treatment for vernalization in certain biennial plants.

16. Practical applications
 Due to vernalization the vegetative period of the plant is cut short
resulting in early flowering.
 Vernalization increases the resistance of plants to fungal diseases.
 It increases the cold resistance of plants.
 In the biennials, vernalization induces early flowering and early fruit
setting.
 Flowering can be induced by grafting and this feature is used in
horticulture.
 It also helps in crop improvement.

17. References:
 Plant physiology,3rd edition by Lincoln and Taiz.
 Introduction to plant Physiology 4th edition by
William G.Hopkins and Norman P.A.H.
 www.pdfdrive.net
 http://en.wikipedia.org/wiki/vernalization
 http://www.plantphysiology.org