❄️ Vernalisation Requirements
Different plants have different needs, but in general:
- 🌡️ Temperature: Around 4°C (just above freezing) works best.
- 🕐 Time: The cold exposure must last from a few days (minimum 4) to a few months (up to 3 months).
- 📍 Where in the plant? The cold must reach the growing point (shoot apex or embryo), not just touch the leaves.
🧪 Example:
Carrot is a biennial plant. It grows only roots in the first year. If it experiences cold during winter, it will grow flowers in the second year.
🌸 Is Vernalisation Always Necessary?
There are two types of responses to vernalisation:
- Obligatory (Absolute) Vernalisation
- The plant must go through a cold period, otherwise it will never flower.
- Example: Some varieties of wheat and cabbage.
- Facultative Vernalisation
- The plant can flower without cold, but vernalisation helps or speeds up the process.
- Example: Some types of barley or grass.
🌿 Vernalisation Hormone: Vernalin
Scientists believe that cold temperatures cause the plant to produce a special hormone called vernalin.
👉 What is a hormone?
In plants, hormones are chemical messengers that move from one part of the plant to another and tell it what to do (like when to grow, when to flower, etc.).
Vernalin is thought to:
- Be produced in the shoot apex or embryo when exposed to cold
- Travel through the plant
- Trigger flowering
(Note: Vernalin is a hypothetical hormone—scientists haven’t isolated it clearly, but they see its effects.)
🌞❄️ Why Are Vernalisation and Photoperiodism Important Together?
Both photoperiodism (response to day length) and vernalisation (response to cold) work together to:
- 🌿 Ensure flowering happens at the right time
– Plants flower in spring or summer, not in the middle of winter. - 🧬 Promote cross-pollination
– If all the plants of the same species flower at the same time, they can pollinate each other, which improves genetic diversity. That means stronger and healthier next generations.
🧪 Example:
Imagine all strawberry plants in a region flowering in the same week. Bees can carry pollen easily between them. But if one plant flowers in January and another in April, cross-pollination won’t happen.
🌾 In Simple Terms
Let’s say you’re a carrot plant. You grow for one year and store food in your root. But you won’t make flowers yet.
Then winter comes. It’s cold. You feel the chill in your growing tip.
You think, “Ah, I’ve been through winter. It must be time to flower now.”
When spring comes and the temperature warms up, you start growing flowers. That is vernalisation at work.
📝 Summary Table
| Feature | Vernalisation | Photoperiodism |
| Stimulus | Cold temperature | Light duration (day/night) |
| Receptor site | Shoot apex or embryo | Leaves |
| Hormone | Vernalin (hypothetical) | Florigen |
| Function | Promotes flowering after winter | Promotes flowering according to season |
| Plants affected | Biennials, perennials | All types, varies by species |