Molar Solution (Molarity, M) in MS Media
A molar solution contains 1 mole of solute dissolved in 1 liter (L) of solution. In the context of the Murashige and Skoog (MS) medium, molarity is used to prepare stock solutions of macronutrients, micronutrients, and plant growth regulators.
For example, MS medium contains 1650 mg/L of NH₄NO₃. To determine its molarity:
Molarity (M) is calculated using the formula Molarity (M) = Mass (g/L) ÷ Molecular Weight (g/mol). In the case of NH₄NO₃ in MS medium, the given concentration is 1.65 g/L, and the molecular weight of NH₄NO₃ is 80.04 g/mol. By applying the formula, M = 1.65 g/L ÷ 80.04 g/mol, the resulting molarity is 0.0206 M, meaning the concentration of NH₄NO₃ in MS medium is approximately 20.6 mM.
So, NH₄NO₃ in MS medium is approximately 20.6 mM.
PPM (Parts Per Million) in MS Media
PPM represents 1 part of solute per 1 million parts of solution and is commonly used to express micronutrient concentrations in MS medium. The formula is:
For example, Fe-EDTA in MS medium is 36.7 mg/L, which means its concentration is 36.7 PPM.
Another example: CuSO₄·5H₂O is present at 0.025 mg/L in MS medium, meaning its concentration is 0.025 PPM (or 25 PPB – parts per billion).
Percent Solution (%) in MS Media
A percent solution expresses concentration as a percentage of solute per 100 mL of solution and is commonly used for stock solutions of sucrose, agar, and hormones in MS media.
- Weight/Volume (% w/v) → Sucrose (3% w/v) in MS medium means 3 g of sucrose is dissolved in 100 mL of solution (or 30 g/L).
- Weight/Weight (% w/w) → Used in dry media preparations where solid components are mixed by weight.
- Volume/Volume (% v/v) → Used for liquid plant growth regulators like 1% stock solution of NAA (1-Naphthaleneacetic acid), meaning 1 mL of NAA dissolved in 100 mL of solvent (usually ethanol or water).
