In plant tissue culture, the choice of gelling agent affects gel strength, transparency, nutrient diffusion, explant stability, and reproducibility.
Agar and low-acyl gellan gum are the two most widely used solidifying agents.
The following layout provides a clean, structured comparison suitable for technical communication with customers.
1. Key Differences Overview
| Parameter | Agar | Low-Acyl Gellan Gum |
|---|
| Source | Seaweed extract | Fermentation-derived polysaccharide |
| Purity | Moderate; natural impurities | High purity; consistent batches |
| Clarity | Opaque to semi-clear | Water-clear |
| Gel Strength | Moderate, variable | Strong, crisp, uniform |
| Dosage | 6–10 g/L | 2.0–3.5 g/L |
| Texture | Soft, elastic | Firm, stable |
| Sensitivity (pH / Ca²⁺) | Low | High |
| Cost Efficiency | Low per kg | High per kg but efficient per liter |
2. Advantages and Limitations
2.1 Agar
| Advantages | Limitations |
|---|
| Easy to prepare; wide tolerance | Natural impurities may inhibit growth |
| Low cost, widely available | Lot-to-lot variation |
| Suitable for rooting stages | Poor clarity; harder to observe contamination |
| Less sensitive to ions | Requires higher dosage (6–10 g/L) |
| Good moisture retention | May increase hyperhydricity risk |
2.2 Low-Acyl Gellan Gum(Gelrite / Phytagel / E418)
Low-acyl gellan gum—also known as Gelrite, Phytagel, or Gellan Gum E418—is widely preferred in modern plant tissue culture for its high clarity and consistent gel performance.
| Advantages | Limitations |
|---|
| Exceptional clarity for monitoring | Sensitive to pH and Ca²⁺ levels |
| High purity → reproducibility | Requires correct premixing to avoid clumping |
| Lower dosage (2.0–3.5 g/L) | Higher cost per kg |
| Firm, stable gel prevents sinking | Over-hardening possible with excess ions |
| Ideal for micropropagation, embryos, seedlings | — |
3. Correct Use of Agar
| Step | Description |
|---|
| Dosage | 6–10 g/L |
| Dissolution | Add agar to medium before heating; boil until fully dissolved |
| Sterilization | Autoclave at 121 °C for 15–20 minutes |
| Pouring Temperature | 45–55 °C |
| Notes | Ensure complete dissolution; avoid over-soft gels; adjust firmness by ±1–2 g/L |
4. Correct Use of Low-Acyl Gellan Gum
4.1 Recommended Concentration
| Dosage Range | Application Characteristics |
|---|
| 2.0–2.4 g/L | Medium firmness; seedlings and general culture |
| 2.5–3.0 g/L | Standard for shoots, callus, and multiplication |
| 3.0–3.5 g/L | Extra firmness; ion-rich media or heavy explants |
■ NOTE
Working concentration may vary with medium composition, ionic strength, and species response.Adjust gellan gum by ±0.1–0.2 g/L per iteration when modifying gel firmness.
Avoid high Ca²⁺/Mg²⁺, Kanamycin, and EDTA, as they may influence gel strength or clarity.
4.2 Dissolution & Sterilization Procedure (Dry Premix Method – Recommended)
Preparation Flowchart
| Stage | Key Actions |
|---|
| ① Weighing | Measure MS salts, vitamins, sucrose, gellan gum |
| ② Dry Premixing | Mix gellan gum with sucrose or part of MS salts (1:5–1:10) for even dispersion |
| ③ Initial Dissolution | Add premixed powders into 80–90% of water while stirring; use mild heat until uniform |
| ④ Adjustments | Top up water to final volume; adjust pH to 5.6–5.8 |
| ⑤ Sterilization | Autoclave at 121 °C for 15–20 minutes |
| ⑥ Dispensing | Cool to 45–55 °C; dispense under sterile conditions |
Critical Control Points (CCPs)
| CCP | Importance |
|---|
| Dry premixing | Prevents clumping and ensures uniform gel strength |
| Correct pH (5.6–5.8) | Determines final gel firmness; pH shifts cause soft or brittle gels |
| Ion sensitivity | Excess Ca²⁺ hardens the gel; avoid adding extra unless required |
| Cooling temperature | 45–55 °C ensures pouring without premature gelation |
4.3 Troubleshooting Guide
| Problem | Likely Cause | Correction |
|---|
| Gel too hard / brittle | pH < 5.5 or excess Ca²⁺ | Adjust pH; reduce ions; decrease gellan gum |
| Gel too soft | pH > 6.0 or low dosage | Adjust pH; increase gellan gum |
| Clumping | Gellan gum added directly to hot water | Use dry premix method |
| Hyperhydricity | Medium too firm or poor gas exchange | Lower gel concentration; improve ventilation |
5. Selection Guide
| Use Case | Recommended Gelling Agent |
|---|
| Low budget, general rooting | Agar |
| Species tolerant to impurities | Agar |
| Need for clear observation | Gellan Gum |
| Sensitive or high-value plant lines | Gellan Gum |
| High reproducibility required | Gellan Gum |
| Automated or imaging workflow | Gellan Gum |
🌱 Related Reading · Plant Tissue Culture Series
