Vernalisering

Vernalisering, or vernalization, is a physiological process in which prolonged exposure to cold induces flowering or accelerates flowering in plants that require a cold period to flower. It is common in many temperate species, particularly winter annuals and perennials such as wheat, barley, rye, and many biennials, as well as some dicot crops and ornamental plants. The response ensures that flowering occurs after winter, in spring, when conditions are favorable.

In the model plant Arabidopsis thaliana and related species, vernalization acts through epigenetic silencing of floral repressors. Prolonged cold triggers the expression of VIN3 and related factors, which recruit Polycomb repressive complexes to the FLOWERING LOCUS C (FLC) locus, leading to histone modifications that repress FLC. Once FLC is repressed, plants become competent to flower when they experience appropriate cues such as sufficient day length or warmth. The repression is stable through subsequent growth, allowing flowering after winter.

In cereal crops such as wheat and barley, vernalization involves a somewhat different gene network, including VRN1, VRN2, and VRN3. Prolonged cold suppresses VRN2 (a repressor) and permits VRN1 and VRN3 (FT-like) to promote flowering. The vernalization requirement is often intertwined with photoperiod responses, so both cold exposure and day length influence flowering time.

Duration and temperature for vernalization are species dependent, typically requiring several weeks of cold at near-freezing temperatures. If vernalization is insufficient, flowering may be delayed or aborted. Understanding vernalization has practical implications for breeding and crop management, enabling adaptation to different climates and seasonal schedules.