2. Vernalization is the process by
which flowering is induced by
prolonged exposure to cold.
*
3. *
*Many plants do not produce flower before they
experience a low temperature.
*This process was first explained by Lysenko
(1928), a Russian scientists, that the cold-
requiring biennial plants can be made to flower in
one growing season by providing low
temperature treatment to young plants.
* He called the effect of this chilling treatment as
vernalisation.
4. *
*Phasic development theory was put forward by a
Russian plant physiologist Lysenko. According to
this theory every plant passes through two phases
of development. These phases are thermophase
and photophase.
5. *
*Thermophase : A temperature required by
plant for development is called thermophase.
* Photophase: The late phase of life in which
plant require definite light requirement for
flowering is called photophase.
6. *
*Experiments have shown that vernalization
treatments are effective only when the excised
embryo is supplied with carbohydrate and
oxygen.
*Lang and Melcher postulated that hormone called
vernalin is produced on the meristematic shoot
apex of the embryo due to vernalization treatment
which is responsible for inducing
8. *
*Site of perception of cold stimulus is different in
different plants. It can be
*a germinating seed
* metabolically active embryo (secale cereale)
* shoot apical meristem (Chrysanthmum)
* vegetative parts such as leaves (Hyoscyamus
niger and other biennials).
11. *
*The stimulus of vernalisation was named as
vernalin.
* Melchers (1936, 1937) observed it in henbane
plants (Hyoscyamus niger) .
*He also explained about the translocation of
venalisation stimulus between grafted union.
13. *
*The formation of vernalin is not enough to bring
about vernalisation.
*In addition, a suitable day length is also necessary.
* It is postulated that in the appropriate
photoperiod, either vernalin is converted into
florigen or vernalin regulates the synthesis of
florigen from precursors.
*Florigen then induces the vegetative meristems to
switch over to reproductive development. This
initiates the process of flower differentiation.
14. *
*(i) Vernalisation can help in shortening the
juvenile or vegetative period of plant and induce
early flowering.
*(ii) It increases yield, resistance to cold and
diseases.
*(iii) ‘Kernel wrinkles’ of Triticale can be removed
by vernalisation.
15. *(iv) It enables the biennials to behave as annuals.
*(v) Plants can be grown in such regions where
normally they do not grow.
