Macronutrient composition in plant cell culture: Which set correctly lists the major macronutrients commonly included in standard media formulations?

Introduction / Context:
Successful plant tissue culture depends on supplying essential mineral elements at appropriate concentrations. Macronutrients are required in millimolar amounts and underpin osmotic balance, metabolism, and morphogenesis.

Given Data / Assumptions:

• Macronutrients in standard media (e.g., MS) include nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur.
• Some answer sets approximate this list but include ions less typical as macronutrients in these media (e.g., sodium).

Concept / Approach:
While several ions appear in trace or optional roles, core macronutrients emphasize N, P, K, Ca, Mg, and S. Among the given choices, the closest correct grouping that avoids sodium or omitting sulfur is selected.

Step-by-Step Solution:

Verification / Alternative check:
MS medium lists NH4+ and NO3− (N), KH2PO4 (P), K+ (K), CaCl2 (Ca), MgSO4 (Mg, S) as standard macronutrient salts.

Why Other Options Are Wrong:

• Sets including Na or Cl as macronutrients (b, d) do not reflect standard macronutrient emphasis in plant culture media.
• Option a includes Na and omits Ca.
• Option e includes Mg but omits Ca, which is standard.

Common Pitfalls:
Confusing plant physiological macronutrients with those specifically emphasized in tissue culture formulations; overvaluing sodium, which is generally not a required macronutrient for most plants.

Final Answer:
N, P, K, S, Ca