Question:
Amino acid tryptophan is used as a precursor for the synthesis of
Amino acid tryptophan is used as a precursor for the synthesis of
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Precursor Summary:
Auxin (IAA) $\rightarrow$ Tryptophan
Ethylene $\rightarrow$ Methionine
Gibberellins (GA) $\rightarrow$ Kaurene/Acetyl-CoA
Cytokinin $\rightarrow$ Adenine
Auxin (IAA) $\rightarrow$ Tryptophan
Ethylene $\rightarrow$ Methionine
Gibberellins (GA) $\rightarrow$ Kaurene/Acetyl-CoA
Cytokinin $\rightarrow$ Adenine
Updated On: Jul 29, 2026
- GA
- IAA
- Ethylene
- Cytokinin
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
Plant hormones (phytohormones) are organic compounds synthesized in trace amounts in one part of the plant and translocated to other parts, where they influence physiological processes.
The biosynthesis of these hormones occurs through highly conserved metabolic pathways starting from primary metabolic precursors, typically amino acids or intermediates of respiration.
Identifying these precursors is a fundamental aspect of plant physiology and biochemistry.
Step 2: Detailed Explanation:
Indole-3-Acetic Acid (IAA) is the most common naturally occurring auxin in plants, regulating cell elongation, apical dominance, root initiation, and vascular differentiation.
The primary pathway for IAA biosynthesis is the tryptophan-dependent pathway.
Tryptophan is an essential aromatic amino acid containing an indole ring.
Through several enzymatic steps, tryptophan is converted into IAA.
This conversion occurs via intermediate pathways like the Indole-3-Pyruvic Acid (IPA) pathway, the Tryptamine (TAM) pathway, or the Indole-3-Acetonitrile (IAN) pathway.
In these pathways, the indole ring structure of tryptophan is preserved to form the core of the IAA molecule.
To address the other plant hormones:
Gibberellic Acid (GA) is synthesized via the terpenoid pathway, starting from acetyl-CoA and passing through mevalonic acid (MVA) and geranylgeranyl pyrophosphate (GGPP) intermediates.
Ethylene is a simple gaseous hormone synthesized from the sulfur-containing amino acid methionine via the S-adenosylmethionine (SAM) and 1-aminocyclopropane-1-carboxylic acid (ACC) pathway.
Cytokinins are synthesized from adenine derivatives (isoprenoid pathway) starting with adenosine monophosphate (AMP) and dimethylallyl pyrophosphate (DMAPP).
Step 3: Final Answer:
Thus, the amino acid tryptophan serves as the biochemical precursor for the synthesis of the auxin Indole-3-Acetic Acid (IAA).
Plant hormones (phytohormones) are organic compounds synthesized in trace amounts in one part of the plant and translocated to other parts, where they influence physiological processes.
The biosynthesis of these hormones occurs through highly conserved metabolic pathways starting from primary metabolic precursors, typically amino acids or intermediates of respiration.
Identifying these precursors is a fundamental aspect of plant physiology and biochemistry.
Step 2: Detailed Explanation:
Indole-3-Acetic Acid (IAA) is the most common naturally occurring auxin in plants, regulating cell elongation, apical dominance, root initiation, and vascular differentiation.
The primary pathway for IAA biosynthesis is the tryptophan-dependent pathway.
Tryptophan is an essential aromatic amino acid containing an indole ring.
Through several enzymatic steps, tryptophan is converted into IAA.
This conversion occurs via intermediate pathways like the Indole-3-Pyruvic Acid (IPA) pathway, the Tryptamine (TAM) pathway, or the Indole-3-Acetonitrile (IAN) pathway.
In these pathways, the indole ring structure of tryptophan is preserved to form the core of the IAA molecule.
To address the other plant hormones:
Gibberellic Acid (GA) is synthesized via the terpenoid pathway, starting from acetyl-CoA and passing through mevalonic acid (MVA) and geranylgeranyl pyrophosphate (GGPP) intermediates.
Ethylene is a simple gaseous hormone synthesized from the sulfur-containing amino acid methionine via the S-adenosylmethionine (SAM) and 1-aminocyclopropane-1-carboxylic acid (ACC) pathway.
Cytokinins are synthesized from adenine derivatives (isoprenoid pathway) starting with adenosine monophosphate (AMP) and dimethylallyl pyrophosphate (DMAPP).
Step 3: Final Answer:
Thus, the amino acid tryptophan serves as the biochemical precursor for the synthesis of the auxin Indole-3-Acetic Acid (IAA).
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