Vernalization — Complete Key Points
Definition: The requirement of a prolonged cold treatment period to induce or accelerate the ability to flower.
Temperature: 0–5°C (near-freezing; above freezing to avoid ice damage)
Duration: Species-specific; typically weeks to months of cold
Plants Requiring Vernalization:
- Winter annuals: Winter varieties of wheat (Triticum aestivum cv. winter)
- Biennials: Carrot (Daucus carota), Beet (Beta vulgaris), Henbane (Hyoscyamus)
- Some perennials
What Vernalization Does:
- Creates an epigenetic memory of cold exposure
- The plant "remembers" having experienced cold even after temperatures rise
- This memory persists through cell divisions (mitotically stable)
Molecular Mechanism (NEET Advanced Knowledge):
- FLC (FLOWERING LOCUS C) encodes a floral repressor protein
- Before cold: FLC highly expressed → FLC protein represses flowering genes (FT)
- During cold: Polycomb Repressive Complex 2 (PRC2) recruited to FLC locus
- PRC2 deposits H3K27me3 (histone methylation) — silences FLC
- After cold: FLC stably silenced → FT can be expressed → Flowering
- Reset: H3K27me3 marks removed in germ cells → next generation starts fresh
Comparison: Vernalization vs Photoperiodism
| Feature | Vernalization | Photoperiodism |
|---|---|---|
| Signal | Cold temperature (0–5°C) | Light/dark ratio |
| Perception site | Shoot apex (meristem) | Leaves |
| Signal molecule | Temperature (physical) | Phytochrome (molecular) |
| Memory | Epigenetic (H3K27me3) | Not epigenetic |
| Season | Winter | Year-round (varies by latitude) |
| Examples | Winter wheat, carrot | Rice (SDP), wheat (LDP) |
Devernalization: If the cold period is followed immediately by high temperatures (before plants mature), the vernalization effect can be reversed (removed). This indicates the epigenetic mark has not yet been fully established.