Neutralized activated charcoal in young regenerating cultures is sometimes added to the medium to achieve which purpose(s)?
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ARemove toxic phenolic compounds released by stressed explants
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BAdsorb and reduce previously added plant growth regulators
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CBoth (a) and (b)
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DMaintain the medium pH directly
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ESupply micronutrients bound to the charcoal
Answer
Correct Answer: Both (a) and (b)
Explanation
Introduction / Context:Activated charcoal (AC) is a high-surface-area adsorbent sometimes included in plant tissue culture media, particularly during regeneration phases. Its use must be intentional because it can significantly change medium chemistry.
Given Data / Assumptions:
- Explants under stress can exude phenolic compounds that oxidize and inhibit growth.
- Carryover or residual PGRs may hinder phase transitions (e.g., from callus to organogenesis).
- Neutralized AC minimizes pH shock but still adsorbs molecules.
Concept / Approach:AC binds small aromatic and hydrophobic molecules, reducing phytotoxic phenolics and lowering free concentrations of auxins/cytokinins if desired. This can improve morphogenesis quality and reduce browning. It does not directly buffer pH like a designated buffer system.
Step-by-Step Solution:
List primary benefits: detoxification of phenolics and removal of excess PGRs.Match to options: (a) and (b) are both correct.Select “Both (a) and (b).”Verification / Alternative check:Protocol notes commonly caution that AC may also remove vitamins or other organics, evidencing its broad adsorptive action.
Why Other Options Are Wrong:
- Maintain the pH: AC is not a primary pH buffer.
- Supply micronutrients: not a controlled nutrient source.
Common Pitfalls:Unintended adsorption of beneficial components (e.g., vitamins, hormones); using AC without adjusting PGR/vitamin levels accordingly.
Final Answer:Both (a) and (b)