In many plants, temperature has a profound effect on flowering. Some plants do not flower unless they are exposed to prolonged periods of cold temperatures. Biennials remain vegetative during the first season, and after being exposed to the cold temperatures of winter, they flower in spring. Majority of plants will not flower if they are not subjected to exposure and will grow vegetatively for an indefinite period.
However, if they are subjected to cold treatment followed by correct photoperiod, they will flower. For example, the biennial henbane (Hyoscyamus niger) a long day plant, can be made to flower within one growing season, provided it is exposed to low temperatures followed by the correct photoperiod.
The term vernalization has been coined to explain the effect of chilling treatment that prepares a plant to flower. Vernalization is defined as the method of inducing early flowering in plants by pretreatment of their seeds at very low temperature. Chourad (1960) has defined it as the acquisition of acceleration of the ability to flower by chilling treatment.
For vernalization, the seeds are allowed to germinate for some time and then are given cold treatment by keeping them at 0-5°C.
The period of cold treatment varies from few days to many weeks from species to species. After the cold treatment, seedlings are allowed to dry for some time and then sown. They should not be sown immediately after the cold treatment.
Thus vernalization prepares the plant to flower whereas the photoperiodic stimulus not only prepares the plant for flowering but also induces it. The shoot tip is the part that perceives the stimulus of cold temperatures. The stimulus is then translocated to other parts of the plant, In some plants, application of gibberellin may replace the cold treatment.
Vernalization is defined as the method of inducing early flowering in plants by pretreatment of their seeds at very low temperatures. Chourad (1960) has defined it as the acquisition or acceleration of the ability to flower by chilling treatment. Hyoscyamus niger has two types, one is annual and the other is biennial. Both of them are long day plants and when exposed to short day will grow vegetatively.
Even the biennial type can be made to flower if its ten days old seedlings are subjected to cold treatments. For vernalization the seeds are allowed to germinate for some time and then are given cold treatment by keeping them at 0-5°C. The period of cold treatment varies from few days to many weeks from species to species.
Temperature as a vernalization effect as well as during photoperiodic treatments has been found to be an important factor regulating flowering. There is evidence to suggest that vernalization effect could involve such substances as gibberellins. The interaction between photoperiod and temperature is considered important in the flowering of many crop plants.