About Lesson
1. Introduction
Plant growth regulators (PGRs) are the molecular switches of tissue culture. They control:
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Callus induction
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Shoot and root formation
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Embryogenesis
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Maturation and elongation
The choice and balance of PGRs determine what kind of plant structures develop in culture.
2. Auxins: Root and Callus Induction
Auxins promote:
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Cell elongation and expansion
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Root initiation
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Callus formation (at high concentrations)
| Auxin | Properties |
|---|---|
| IAA | Natural, but rapidly degraded by light/oxidation |
| IBA | Synthetic; stable; effective in rooting woody plants |
| NAA | Very stable; strong callus and root inducer |
| 2,4-D | Powerful callus inducer; often used for somatic embryogenesis in crops like maize or wheat |
3. Cytokinins: Shoot Multiplication
Cytokinins drive:
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Cell division
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Shoot bud formation
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Inhibition of root elongation
| Cytokinin | Notes |
|---|---|
| BAP | Highly effective in most species; economical |
| Kinetin | Older; still widely used for shoot cultures |
| Zeatin | Less toxic; used for delicate or sensitive species |
| TDZ | Very potent; works well for woody or recalcitrant plants |
4. Auxin–Cytokinin Ratios
This ratio guides morphogenesis:
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High auxin, low cytokinin → Roots
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High cytokinin, low auxin → Shoots
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Balanced → Callus or undifferentiated tissue
Tip: Begin with published concentrations, then test different ratios for your specific species and goal.
5. Other PGRs and Modulators
| Type | Function |
|---|---|
| Gibberellins (GA) | Promote elongation; break dormancy |
| Abscisic Acid (ABA) | Induces dormancy; used to mature somatic embryos |
| Ethylene Inhibitors (e.g., AgNO₃) | Reduce senescence in flower cultures |
| Brassinosteroids | Improve vigor; under research for tissue culture use |