Which of the following substances is NOT a cytokinin used in plant tissue culture?
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A2,4-dichlorophenoxyacetic acid (2,4-D)
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B6-benzylaminopurine (BAP/BA)
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CZeatin
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DKinetin
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EThidiazuron (TDZ)
Answer
Correct Answer: 2,4-dichlorophenoxyacetic acid (2,4-D)
Explanation
Introduction / Context:Cytokinins promote cell division and shoot formation. Distinguishing cytokinins from auxins prevents hormonal misapplication during in vitro morphogenesis and regeneration protocols.
Given Data / Assumptions:
- BAP, zeatin, kinetin, and TDZ are commonly used cytokinins or cytokinin-like compounds.
- 2,4-D is a synthetic auxin, not a cytokinin.
Concept / Approach:Identify each compound’s hormone class. 2,4-D is used mainly for callus induction and somatic embryogenesis as an auxin. The others are standard cytokinins for shoot induction and proliferation.
Step-by-Step Solution:
Classify each option by hormone type.Recognize that 2,4-D is an auxin, unlike the others.Select 2,4-D as the item that is not a cytokinin.Verification / Alternative check:Hormone supplier catalogs and tissue culture manuals classify these compounds accordingly.
Why Other Options Are Wrong:
- BAP, zeatin, kinetin, TDZ: all act as cytokinins or cytokinin-like regulators.
Common Pitfalls:Confusing frequent use of 2,4-D in callus protocols with cytokinin function; assuming all “shoot-promoting” media contain only cytokinins without considering ratios.
Final Answer:2,4-dichlorophenoxyacetic acid (2,4-D)