Tutorial: preparing MS medium, step by step

Murashige and Skoog (MS) medium, published in 1962, is still the starting point for most plant tissue culture work. Below is a practical walk-through for one litre of solid medium. Adjust hormones to your plant and stage.

What you need

• MS basal salts (ready-made powder or your own stock solutions)
• Sucrose – usually 30 g per litre
• Gelling agent – agar at around 7–8 g/L, or a gellan gum at lower rates
• Plant growth regulators as needed (for example a cytokinin such as BAP for multiplication, an auxin such as IBA or NAA for rooting)
• Distilled or RO water, pH meter, 1 N NaOH and 1 N HCl, measuring cylinder, culture vessels, autoclave

Method

1. 1Pour about 700–800 mL of water into a beaker on a stirrer.
2. 2Add the MS salts (or the correct volume of each stock) and let them dissolve fully.
3. 3Add the sucrose and any vitamins and growth regulators.
4. 4Top up to just under 1 L.
5. 5Adjust pH to 5.7–5.8 with NaOH or HCl, adding a drop at a time.
6. 6Make up to exactly 1 L.
7. 7Add agar and heat gently while stirring until it dissolves and the liquid turns clear.
8. 8Dispense into vessels and close them.
9. 9Autoclave at 121 °C (about 15 psi) for 15–20 minutes. Bigger volumes need longer.
10. 10Let the medium set and store it clean and dark. Use within a couple of weeks.

Common problems

• Soft or runny medium: pH too low, too little agar, or over-autoclaving.
• Browning explants: phenolics released from cut tissue. Try antioxidants, darkness for the first days, or frequent transfers.
• Glassy, water-soaked shoots (hyperhydricity): often too much cytokinin, too soft a gel, or poor air exchange.
• Contamination a few days after plating: usually a sterility issue at the hood, not the medium itself.

Label every batch with the date, formula and pH. When something goes wrong three weeks later, that label is how you work out why.