Why Vernalization is Necessary for Plants?

Why Vernalization is Necessary for  Plants?

Read about Definition, History, Importance of vernalization and its mechanism.

Definition:-
The word vernalization is coming from Latin word "vernus" which means " of the spring." Its definition is "The low temperature treatment given to the seed or plant for stimulating flowering in them is called vernalization. Or it is "The acquisition of a plant's ability to flower in the spring by exposure to the long period of winter or by artificial cooling.

Discovery:-
The phenomenon of vernalization is discovered by J. Gustave Gassner in 1928. He was a German plant physiologist. He was working with rye (Secale cereale). He found that temperature is critical during early stages of seed germination. He showed flowering and fruiting depends on temperature during this critical stage.

Explanation;-
Seed is given low temperature treatment during vernalization. It's effect persists and flowering takes place much later. Thus the effect of vernalization is inductive in nature. Therefore' the plant need not be exposed to low temperature at the time of flowering.

Sites of vernalization:-
1: Stem tip ---> The localized cooling treatment was given to stem tip. It receives the vernalization effect.
2: Seed ---> Seeds are vernalized before sowing. The embryo in seed receives the vernalization stimulus. When seeds are sown, it produces flowers.
3: Root tips and leaves ---> The root tips and leaves of certain plants contain dividing cells. Therefore its root tips and leaves can be vernalized.

Mechanism of Vernalization:-
In 1968, Mikhail Chailakhyan suggested that two substances involves in flower formation. One is gibberellin or gibberellin like substances and second is anthesin. Anthesin is hypothetical substance like vernaline. He suggested that vernalization requiring plants produce vernalin when subjected to low temperatures. The vernalin is then converted to gibberellin in long days. Gibberellin cause flowering in the presence of vernalin.

Factors affecting Vernalization:-
1: Water and Oxygen ---> Seed need to imbibe 20-30% water. Therefore, dry seed cannot be vernalized.
2: Temperature ---> The seeds are exposed to low temperature during vernalization. This temperature ranges from 1-7.

3:  Food Substances ---> Food substances are required for vernalization. Isolated embyos cannot be vernalized.

4: Effect of Light ---> Light has no effect on vernalization. Therefore, a seed of  a plant can be sown in the presence oe absence of light.

5: Effect of Harmones ---> The requirement of vernalization can be replaced by the application of gibberellic acid. It causes bolting and flowering.