VERNALISATION

• Plants have evolve the ability to alter their developmental programme in response to environmental stimuli. 
• A major switch in the development programme is the transition to flowering. Photoperiod and temperature play an important role in determining the  correct time to flower.
• Vernalisation is also called  as Chilling treatment/ Cold treatment.
• Many flowers don't come to flower before they experience a low temperature. 
• These plants remain vegetative during warm season experience low temperature during winter grow further  and  bear flowers and fruits
•              VERNALISATION
• Promotion of flowering by giving cold treatment  is called VERNALISATION. 
• The effective temperature range for vernalisation is from just below freezing to >10°C ,with  a broad optimum usually  between about 1-5°C.
• Vernalisation is the process in plants  where the  flowering is promoted by a cold treatment given to a fully hydrated seed (i.e a seed that has imbibed water )or to a growing plant. 
• Photoperiodism and vernalisation are to most important mechanisms underlying seasonal responses. Photoperiodism -is response to the length of the day whereas Vernalisation-is the promotion of flowering. 
• Without the cold treatment  plant that requires vernalisation show delayed flowering or remain vegetative. In many cases these plants grow as russettes(with no elongation of stem).
• Competence of the meristem to undergo the floral transition.
• After vernalisation,plants do not necessarily initiate flowering but acquires the competence to do so.
• It is reversible and can be lost as a result to de-vernalisation with conditions such as high temperatures. 
• According to studies show , the apical meristem is the site of cold perception during vernalisation and that vernalisation causes the meristem to become competent to flower. 
• Later there comes a hypothesis that the VERNALIN compound  is responsible for vernalisation stimulus which produced in plants after vernalisation process. 
• Vernalin got activated at low temperature. 
• "VERNALIN has not been isolated yet ".

• Hence vernalisation is a process in plants where juvenile or vegetative phase is shortened and flowering is induced by a cold treatment. 
• An example of  Winter rye  may be quoted here. When the seeds of this variety of rye  were germinated at 1°C for 4 weeks, the plant flowered 11 weeks after planting,but at the same time seed germinated at 18°C did not have  flowering  shoot in the same duration. 
• Vernalisation  occurs in dry seeds . The seed must be germinated so that they contain an active embryo . Due to this reason , the seeds are moistened before exposing them to low temperature. For a complete plant an active meristem is required. 
• The stimulus recieved by the actively dividing cells of shoot or embryo travels to all parts of the plant and prepare it to flower. This stimulus has been named VERNALIN. 
• Attempts to isolate and chemically identify Vernalin haven't been succeeded 
• However Anton lang have demonstrated that treatment with Gibberllic acid ,a plant hormone substitute for cold treatment in same species plants.

•       MECHANISMS OF FLORAL INDUCTION IN VERNALISED PLANT (Genes involved)
• This process  have been identified in a Arabidopsis Thaliana ,some flowering genes are involved in this process. 
• Some stable changes  are found in the pattern of gene expression in the meristem after cold treatment. 
• FLC gene( Flower  locus C ) -A gene that acts as a repressor of flowering. FLC is highly expressed in non vernalised shoot apical meristem.  In Vernalisation this gene is epigenetically switched off by an unknown mechanism for the remainder of plant's  life cycle,permitting  flowering in response 
• FT gene (flower locus T ) - A genes in leaves,Florigenic factor (flowering gene).
• SOC 1(Supressor of over expression of constan S1)-A gene in shoot apical meristem(flowering  gene)
• FD (Flower locus)-A gene in shoot apical meristem (flowering gene).
• Vernalisation 1&2(VRN 1 AND VRN2)=Activated by cold temperatures 
• Vernalisation insensitive (VRN3)=Activated after VRN 1&2 or after cold temperature. 

If FLC activated- NO FLOWERING 

If FLC is inactive- FLOWERING 

            ●  NO VERNALISATION 

                             |

                 FLC ACTIVATED                                                           
                              |

                       INHIBIT

                  1.FT gene (in leaves)

                  2.FD gene(in apical meristem)

                  3.SOC 1 gene ,flowering  gene (in apical meristem)

                              |

                   NO FLOWERING 

            ●    VERNALISATION 

                               |

                    VRN 1&2ACTIVE

                               |

                     VRN3 ACTIVE

                               |

                      FLC INACTIVE 

                                |

                       FLOWERING