In plant cell culture media, which of the following are recognized disadvantages of using the natural auxin indole-3-acetic acid (IAA)?

Introduction / Context:
Auxins drive cell division, elongation, and callus induction in vitro. Indole-3-acetic acid (IAA) is the principal natural auxin in plants, yet tissue culture practitioners often prefer synthetic auxins because of IAA’s chemical liabilities under culture conditions.

Given Data / Assumptions:

• Aqueous media are exposed to light, oxygen, and sometimes elevated temperature.
• Plant cells possess enzymes that modify and inactivate auxins.
• The question asks for disadvantages specific to IAA.

Concept / Approach:
IAA is chemically labile. It photodegrades and oxidizes, reducing effective concentration. Cells can also conjugate IAA to amino acids or sugars, lowering free auxin levels and altering responses. Consequently, stable analogs (e.g., NAA, 2,4-D, IBA) are common in protocols.

Step-by-Step Solution:

Verification / Alternative check:
Method notes in tissue culture references frequently warn of IAA instability and recommend freshly prepared solutions or alternative auxins.

Why Other Options Are Wrong:

• Single statements (a–c): each is true but incomplete.
• None of the above: contradicts well-documented properties of IAA.

Common Pitfalls:
Using old IAA stocks; neglecting light protection; assuming equal stability among auxins.

Final Answer:
All of the above