Plant Growth Regulators Quick Guide
Contents
- Common Growth Regulators
- Quick Reference Table
- Applications for Cannabis
- Preparation Guide
- Troubleshooting
Common Growth Regulators
Plant growth regulators (PGRs) are naturally occurring or synthetic compounds that modify plant growth and development. Here are the main types used in cannabis cultivation and tissue culture:
| PGR Type | Function | Examples | Cannabis Uses |
|---|---|---|---|
| Auxins | Root initiation, cell enlargement | IBA, NAA, IAA, 2,4-D | Rooting cuttings, callus induction |
| Cytokinins | Shoot initiation, cell division | BAP, Kinetin, TDZ, Zeatin | Shoot multiplication, preventing apical dominance |
| Gibberellins | Stem elongation, germination | GA₃ | Breaking seed dormancy, increasing internode length |
| Ethylene | Ripening, senescence | Ethephon | Usually avoided in tissue culture |
| Abscisic Acid | Dormancy, stress response | ABA | Used for hardening plants, rarely in cannabis culture |
| Polyamines | Stress protection | Putrescine, Spermidine | Supporting growth under stressful conditions |
Quick Reference Table
Auxins
| Compound | Stock Solution | Working Range | Stability | Notes |
|---|---|---|---|---|
| IBA (Indole-3-butyric acid) | 1mg/ml in ethanol | 0.1-5.0 mg/L | Stable in dark | Best for root induction, less toxic than NAA |
| NAA (1-Naphthaleneacetic acid) | 1mg/ml in ethanol | 0.1-2.0 mg/L | Stable | Stronger than IBA, can cause callusing |
| IAA (Indole-3-acetic acid) | 1mg/ml in ethanol | 0.1-10.0 mg/L | Light sensitive | Natural auxin, rapidly degraded |
| 2,4-D (2,4-Dichlorophenoxyacetic acid) | 1mg/ml in ethanol | 0.1-5.0 mg/L | Stable | Potent, mainly for callus induction |
Cytokinins
| Compound | Stock Solution | Working Range | Stability | Notes |
|---|---|---|---|---|
| BAP/BA (6-Benzylaminopurine) | 1mg/ml in 1N NaOH | 0.1-5.0 mg/L | Stable | Most commonly used in cannabis tissue culture |
| Kinetin | 1mg/ml in 1N NaOH | 0.1-10.0 mg/L | Stable | Milder than BAP, less side effects |
| TDZ (Thidiazuron) | 1mg/ml in DMSO | 0.001-1.0 mg/L | Stable | Very potent, can cause hyperhydricity |
| Zeatin | 1mg/ml in 1N NaOH | 0.1-5.0 mg/L | Freeze | Natural cytokinin, expensive |
Others
| Compound | Stock Solution | Working Range | Stability | Notes |
|---|---|---|---|---|
| GA₃ (Gibberellic acid) | 1mg/ml in ethanol | 0.1-5.0 mg/L | Light sensitive | Used for seed germination, rarely in tissue culture |
| Ethephon | 1mg/ml in water | 0.1-10.0 mg/L | pH dependent | Generally avoided in tissue culture |
| PPMâ„¢ (Plant Preservative Mixture) | Use directly | 0.5-4.0 ml/L | Stable | Not a PGR but a biocide often used with PGRs |
Applications for Cannabis
Standard PGR Combinations for Cannabis Tissue Culture
| Goal | Auxin | Cytokinin | Ratio | Medium | Notes |
|---|---|---|---|---|---|
| Explant Establishment | None or IBA 0.1mg/L | BAP 0.5-1.0mg/L | 1:5-10 | MS or ½MS | Higher cytokinin favors shoot development |
| Shoot Multiplication | None | BAP 0.2-0.5mg/L | 0:1 | MS | Low cytokinin prevents hyperhydricity |
| Rooting | IBA 0.5-1.0mg/L | None | 1:0 | ½MS | Lower salt strength promotes rooting |
| Callus Induction | 2,4-D 1.0-2.0mg/L | BAP 0.5-1.0mg/L | 2:1 | MS | High auxin favors callus formation |
| Somatic Embryogenesis | 2,4-D 1.0mg/L then remove | None | Variable | MS then ½MS | Two-stage protocol works best |
Clone Rooting Solutions
| Application | Compound | Concentration | Application Method | Duration |
|---|---|---|---|---|
| Standard Cloning | IBA | 500-1000ppm (0.05-0.1%) | Quick dip | 3-5 seconds |
| Delicate Cuttings | IBA | 100-300ppm (0.01-0.03%) | Extended soak | 5-10 minutes |
| Powder Form | IBA | 0.1-0.8% | Dip stem | Immediate |
| Gel Form | IBA | 0.1-0.6% | Coat stem | Immediate |
| DIY Solution | Willow water | Natural concentration | Extended soak | 24 hours |
Preparation Guide
Making Stock Solutions
For Auxins (IBA, NAA, IAA):
- Dissolve 100mg in 5-10ml of ethanol or isopropanol
- Once dissolved, bring to 100ml with distilled water
- Final concentration: 1mg/ml (1000ppm)
- Store in amber bottle at 4°C for up to 1 month
For Cytokinins (BAP, Kinetin):
- Dissolve 100mg in 5-10ml of 1N NaOH
- Once dissolved, bring to 100ml with distilled water
- Final concentration: 1mg/ml (1000ppm)
- Store at 4°C for up to 3 months
For Filter Sterilization:
- Use 0.22μm syringe filter for all PGR solutions
- Add to autoclaved media after cooling to ~50°C
Quick Calculator
To prepare working concentration:
- 1mg/L = 1ml of 1mg/ml stock solution per liter
- 0.5mg/L = 0.5ml of 1mg/ml stock per liter
- 2mg/L = 2ml of 1mg/ml stock per liter
For cloning solutions:
- 1000ppm = 1g per liter = 0.1%
- To convert percentage to ppm, multiply by 10,000 (0.1% = 1000ppm)
Troubleshooting
| Problem | Possible Cause | Solution |
|---|---|---|
| No shoot induction | Cytokinin concentration too low | Increase BAP to 1.0-2.0mg/L |
| Excessive callus formation | Auxin concentration too high | Reduce auxin or increase cytokinin ratio |
| Hyperhydricity (vitrification) | Cytokinin concentration too high | Reduce BAP to 0.1-0.2mg/L, improve ventilation |
| Poor rooting | Residual cytokinin, insufficient auxin | Transfer to hormone-free media before rooting, then to IBA media |
| Stunted growth | PGR imbalance | Try hormone-free media for one passage |
| Browning after adding PGRs | Ethanol toxicity in stock solution | Dilute stock more before adding to media |
| No response to PGRs | Degraded stock solutions | Prepare fresh solutions, protect from light and heat |
Important: Commercial cannabis growers should be aware that some plant growth regulators are regulated substances in certain jurisdictions. Always verify the regulatory status of PGRs in your location before use. This reference is for educational purposes only.