Vernalisation (Springification)

Vernalisation means promotion/induction of flowering by exposure to a period of low temperature (cold). It is an adaptation seen mainly in temperate plants so that flowering happens after winter, in the favourable season.

Vernalisation = Cold treatment → plant becomes able to flower later.

Why plants need vernalisation?

Some plants (especially winter annuals and biennials) should NOT flower too early. If they flower before becoming strong vegetatively, survival and seed yield reduce.

Cold exposure during winter:

  • prevents precocious (too early) flowering,
  • allows the plant to complete vegetative growth first,
  • then the plant gets the competence/ability to flower when conditions become suitable.

Cold does not directly make flowers immediately — it gives the plant flowering readiness.

Which plants show vernalisation?

A. Winter cereals (winter varieties)

  • Winter wheat, barley, rye are sown in autumn.
  • They grow as seedlings during winter, receive cold exposure, and then flower in spring/summer.

B. Biennials

Biennials normally take two years:

  • Year 1: vegetative growth (often rosette stage)
  • Year 2: after winter cold → flowering (often with bolting)

Examples: cabbage, carrot, sugar beet.

Winter cereals + biennials = classic vernalisation examples.

Conditions required for vernalisation

For vernalisation to be effective:

  • Low temperature is essential (commonly around 0–10°C in NCERT-style notes).
  • Moisture and oxygen are required because living tissues must remain active.
  • It is effective during seed stage or early vegetative stage (young meristems are responsive).

Cold + living active tissue (needs water + O₂).

Site of perception

The cold stimulus is perceived mainly by the apical meristem (shoot apex).

Vernalisation is perceived by the apical meristem.

Vernalin

Like florigen in photoperiodism, a hypothetical substance called vernalin was proposed to explain flowering after cold exposure.

Vernalin is hypothetical; exact chemical nature is not identified as a single hormone.

Quantitative nature of cold requirement

Vernalisation is often a quantitative requirement:

  • a sufficient duration of cold is needed,
  • longer cold (within limits) generally increases effectiveness.

More cold time → stronger vernalisation (up to a limit).

Devernalisation (Reversal)

Devernalisation is the reversal of vernalisation if the plant (after cold treatment) is exposed to high temperature.

  • This can cancel the cold effect.
  • Result: flowering may be delayed or prevented.

High temperature after cold can remove the ‘cold memory’.

Vernalisation vs Photoperiodism

  • Vernalisation: depends on temperature (cold)
  • Photoperiodism: depends on day/night length
  • Both regulate flowering, but they are different signals.

Vernalisation cannot substitute photoperiodism (and vice versa). Some plants may need both.

Important Notes

  1. Vernalisation = cold treatment → flowering ability
  2. Seen in winter cereals and biennials
  3. Perceived by apical meristem
  4. Needs moisture + oxygen (living tissue)
  5. Devernalisation = high temperature reverses cold effect
  6. Vernalisation ≠ photoperiodism (temperature vs day length)

Vernalisation

Definition: Vernalisation = flowering induced by low temperature exposure.

  • Cold makes the plant “ready to flower later.”

  • Examples: Winter wheat/barley + biennials (cabbage, carrot, sugar beet)

  • Site: Apical meristem perceives cold

  • Devernalisation: High temperature after cold can cancel the effect

  • Comparison: Vernalisation = temperature; Photoperiodism = day/night length

💡 Questions and Answers

Q1. Why do biennial plants require vernalisation?

A1: Biennials first need enough time to grow vegetatively (make leaves/rosette and store food). Cold exposure during winter acts like a signal that the plant has completed the winter phase, so it can start flowering in the next season.

  • Key Points: prevents early flowering; ensures vegetative maturity; flowering after winter

Q2. Why is devernalisation harmful for crop yield?

A2 If the cold effect is cancelled by high temperature, the plant may delay flowering or flower irregularly. That means seed/fruit formation happens late or poorly, so yield can reduce.

  • Key Points: reverses cold stimulus; delays flowering; lowers yield

Q3. Which part of plant perceives vernalisation?

A3 : The cold is mainly sensed by the shoot apex (apical meristem), because that is the region that later changes into a flowering meristem.

  • Key Points: apical meristem (shoot apex) is the site of perception