Explain the theories to explain the mechanism of vernalization.

Explanation

Mechanism of Vernalization:
Two main theories to explain the mechanism of vernalization are:
i Hypothesis of phasic development.
ii. Hypothesis of hormonal involvement.
i. Hypothesis of phasic development: According to Lysenko, development of an annual seed plant consists of two phases. First phase is thermostage, which is vegetative phase requiring low temperature and suitable moisture. Next phase is photo stage which requires high temperature for synthesis of florigen (flowering hormone).
ii. Hypothesis of hormonal involvement: According to Purvis (1961), formation of a substance A from its precursor, is converted into B after chilling. The substance B is unstable. At suitable temperature B is converted into stable compound D called Vernalin. Vernalin is converted to F (Florigen). Florigen induces flower formation. At high temperature B is converted to C and devernalization occurs.