Question:
Abscisic acid synthesis in plants involves:
A. Isoprenoid pathway
B. SAM pathway
C. Carotenoid pathway
D. Indole-acetal doxim pathway
Choose the correct answer from the options given below:
Abscisic acid synthesis in plants involves:
A. Isoprenoid pathway
B. SAM pathway
C. Carotenoid pathway
D. Indole-acetal doxim pathway
Choose the correct answer from the options given below:
A. Isoprenoid pathway
B. SAM pathway
C. Carotenoid pathway
D. Indole-acetal doxim pathway
Choose the correct answer from the options given below:
Show Hint
NCED (9-cis-epoxycarotenoid dioxygenase) is the rate-limiting enzyme in ABA biosynthesis. Remember: Plants make ABA from Carotenoids!
Updated On: Aug 21, 2026
- A, B and D only
- A and C only
- C and D only
- B and D only
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Verified By Collegedunia
The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
Abscisic Acid (ABA) is a 15-carbon sesquiterpene hormone. In plants, it is synthesized primarily through the "indirect pathway," which starts from precursors in the chloroplast and moves to the cytosol. This pathway is shared with the synthesis of pigments.
Step 2: Detailed Explanation:
The biosynthesis of ABA involves the following:
1. Isoprenoid Pathway (A): All terpenoids, including ABA, are derived from the basic 5-carbon isoprenoid building blocks (IPP and DMAPP). These are synthesized via the MEP (Methylerythritol phosphate) pathway in plastids. Therefore, ABA is biochemically an isoprenoid derivative.
2. Carotenoid Pathway (C): Unlike some fungi that synthesize ABA directly from farnesyl pyrophosphate (the direct pathway), higher plants use the "indirect pathway." In this route, \(C_{40}\) carotenoids (like \(\beta\)-carotene) are converted into xanthophylls (violaxanthin and neoxanthin). These are then cleaved by the enzyme NCED to produce xanthoxin, a \(C_{15}\) precursor which is finally converted into ABA. Thus, ABA synthesis is fundamentally linked to the carotenoid pathway.
3. SAM Pathway (B): SAM (S-adenosylmethionine) is the precursor for Ethylene and polyamines, not ABA.
4. Indole-acetal doxim pathway (D): This pathway is involved in the synthesis of Auxins (IAA) and glucosinolates, not ABA.
Therefore, only A and C are involved in ABA biosynthesis.
Step 3: Final Answer:
ABA synthesis involves the Isoprenoid and Carotenoid pathways.
Abscisic Acid (ABA) is a 15-carbon sesquiterpene hormone. In plants, it is synthesized primarily through the "indirect pathway," which starts from precursors in the chloroplast and moves to the cytosol. This pathway is shared with the synthesis of pigments.
Step 2: Detailed Explanation:
The biosynthesis of ABA involves the following:
1. Isoprenoid Pathway (A): All terpenoids, including ABA, are derived from the basic 5-carbon isoprenoid building blocks (IPP and DMAPP). These are synthesized via the MEP (Methylerythritol phosphate) pathway in plastids. Therefore, ABA is biochemically an isoprenoid derivative.
2. Carotenoid Pathway (C): Unlike some fungi that synthesize ABA directly from farnesyl pyrophosphate (the direct pathway), higher plants use the "indirect pathway." In this route, \(C_{40}\) carotenoids (like \(\beta\)-carotene) are converted into xanthophylls (violaxanthin and neoxanthin). These are then cleaved by the enzyme NCED to produce xanthoxin, a \(C_{15}\) precursor which is finally converted into ABA. Thus, ABA synthesis is fundamentally linked to the carotenoid pathway.
3. SAM Pathway (B): SAM (S-adenosylmethionine) is the precursor for Ethylene and polyamines, not ABA.
4. Indole-acetal doxim pathway (D): This pathway is involved in the synthesis of Auxins (IAA) and glucosinolates, not ABA.
Therefore, only A and C are involved in ABA biosynthesis.
Step 3: Final Answer:
ABA synthesis involves the Isoprenoid and Carotenoid pathways.
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