In plant tissue culture media used for micropropagation and callus work, auxins and cytokinins are typically supplied at micromolar concentrations. What is the commonly used concentration range for these plant growth regulators (PGRs)?

Introduction / Context:
Plant tissue culture relies on carefully balanced plant growth regulators (PGRs). Auxins and cytokinins are the workhorses for inducing callus, shoots, and roots. Knowing typical concentration ranges helps avoid toxicity and physiological abnormalities while ensuring reliable morphogenesis.

Given Data / Assumptions:

• The question asks for standard, routinely used ranges in general-purpose culture media.
• Auxins (e.g., IAA, NAA, 2,4-D) and cytokinins (e.g., BAP, kinetin, zeatin) are considered.
• Concentrations are expressed in micromolar (μM).

Concept / Approach:
Most protocols for callus induction, somatic embryogenesis, and organogenesis use auxins and cytokinins between low and mid micromolar levels. Excessively high PGR levels can cause vitrification, callus browning, or abnormal shoots/roots. Very low levels may be insufficient to trigger morphogenesis.

Step-by-Step Solution:

Verification / Alternative check:
Protocol collections and plant tissue culture manuals consistently present successful formulations in the low-to-mid μM range for both classes of PGRs.

Why Other Options Are Wrong:

• 50–100 μM and 100–125 μM: often too high for routine morphogenesis; risk of physiological disorders.
• More than 125 μM: typically inhibitory or toxic.
• 0.01–0.5 μM: can work in fine-tuned systems but is not the most common range across species and aims.

Common Pitfalls:
Assuming “more is better” with PGRs; overlooking the critical auxin:cytokinin ratio; ignoring species and tissue differences.

Final Answer:
1–50 μM