Q46. Wheat plants treated with prolonged cold temperature at the seedling stage
flower earlier than the untreated control. Seeds collected from these treated
individuals, however, give rise to plants that do not flower early. This
phenomenon is called
(A) vernalization.
(B) temperature acclimation.
(C) photoperiodism.
(D) adaptation.
The correct answer is (A) vernalization.
Wheat plants exposed to prolonged cold at the seedling stage flower earlier due to a specific physiological process, but this effect does not pass to offspring seeds, which revert to normal flowering time.
Option Analysis
(A) Vernalization matches exactly: it accelerates flowering in winter cereals like wheat via prolonged low temperatures (1-7°C), yet requires revernalization each generation as it’s epigenetic, not genetic.
(B) Temperature acclimation involves physiological adjustments for cold tolerance, like frost resistance, without promoting flowering or resetting in seeds.
(C) Photoperiodism regulates flowering by day length (e.g., long-day wheat), independent of cold, and persists genetically across generations.
(D) Adaptation refers to heritable evolutionary changes for survival, unlike this non-inheritable, reversible response.
Wheat Vernalization Phenomenon Introduction
The wheat vernalization phenomenon occurs when wheat plants treated with prolonged cold temperature at the seedling stage flower earlier than untreated controls, but seeds from these plants revert to normal timing. This non-heritable response ensures winter wheat flowers post-winter, vital for crops in temperate regions. For CSIR NET aspirants, mastering this distinguishes vernalization from photoperiodism.
Vernalization Mechanism in Wheat
Vernalization induces flowering competence via epigenetic changes, like histone modifications on VRN1 genes, silencing repressors (VRN2) after 4-8 weeks at 1-7°C. In wheat seedlings, cold resets the vegetative phase, promoting floral transition upon warming, but progeny require re-exposure. Winter varieties sown in autumn exemplify this for mid-summer harvest.
Differences from Other Options
| Phenomenon | Trigger | Effect on Flowering | Heritability | Wheat Example |
|---|---|---|---|---|
| Vernalization | Prolonged cold (seedling stage) | Earlier flowering, resets in seeds | Non-heritable (epigenetic) | Matches query exactly |
| Temperature Acclimation | Low non-freezing temps | Cold tolerance, no flowering shift | Physiological, reversible | Frost survival, not bloom |
| Photoperiodism | Day length | Long/short day induction | Genetic | Day-neutral variants unaffected |
| Adaptation | Natural selection | Evolutionary survival traits | Heritable (genetic) | Drought-resistant cultivars |
CSIR NET Exam Relevance
This question tests plant physiology distinctions: vernalization (temperature-driven, non-genetic) vs. photoperiodism (light-driven). Practice similar: winter wheat needs cold for VRN1 activation. Key for molecular biology, biotech sections.
