Question:
Which phytohormone is regarded as an anti-stress promoter and growth bio-stimulator?
Which phytohormone is regarded as an anti-stress promoter and growth bio-stimulator?
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Melatonin in plants is emerging as a key molecule that:
Enhances tolerance to various stresses (anti-stress).
Promotes growth and development (growth bio-stimulator).
Jasmonic acid: Primarily defense.
1-MCP: Ethylene inhibitor.
Prohexadione-Ca: Growth retardant.
Updated On: Jul 2, 2026
- Jasmonic acid
- 1-MCP
- Melatonin
- Prohexadione -- Ca
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The Correct Option is C
Approach Solution - 1
The question asks for a phytohormone that acts as both an anti-stress promoter and a growth bio-stimulator.
(1) Jasmonic acid (JA): A phytohormone primarily involved in plant defense responses against herbivores and pathogens, and also in some developmental processes. While it helps plants cope with certain stresses, it's not primarily viewed as a broad growth bio-stimulator in the same way as others.
(2) 1-MCP (1-Methylcyclopropene): An ethylene action inhibitor, used to delay ripening and senescence in fruits and flowers. It's not a growth promoter or a broad anti-stress agent itself.
(3) Melatonin (N-acetyl-5-methoxytryptamine): Originally known for its role in animals, melatonin has been identified as a ubiquitous molecule in plants with diverse functions. It is increasingly recognized as a potent anti-stress compound in plants, helping them tolerate various abiotic stresses (drought, salinity, cold, heat, heavy metals) and biotic stresses. Furthermore, melatonin acts as a growth bio-stimulator, promoting seed germination, root growth, vegetative growth, flowering, and fruit development. It influences many physiological processes and interacts with other phytohormones.
(4) Prohexadione-Ca: A plant growth regulator that inhibits gibberellin biosynthesis, thus acting as a growth retardant, not a bio-stimulator in the sense of promoting overall growth. Therefore, melatonin fits the description of being both an anti-stress promoter and a growth bio-stimulator in plants very well. Melatonin
(1) Jasmonic acid (JA): A phytohormone primarily involved in plant defense responses against herbivores and pathogens, and also in some developmental processes. While it helps plants cope with certain stresses, it's not primarily viewed as a broad growth bio-stimulator in the same way as others.
(2) 1-MCP (1-Methylcyclopropene): An ethylene action inhibitor, used to delay ripening and senescence in fruits and flowers. It's not a growth promoter or a broad anti-stress agent itself.
(3) Melatonin (N-acetyl-5-methoxytryptamine): Originally known for its role in animals, melatonin has been identified as a ubiquitous molecule in plants with diverse functions. It is increasingly recognized as a potent anti-stress compound in plants, helping them tolerate various abiotic stresses (drought, salinity, cold, heat, heavy metals) and biotic stresses. Furthermore, melatonin acts as a growth bio-stimulator, promoting seed germination, root growth, vegetative growth, flowering, and fruit development. It influences many physiological processes and interacts with other phytohormones.
(4) Prohexadione-Ca: A plant growth regulator that inhibits gibberellin biosynthesis, thus acting as a growth retardant, not a bio-stimulator in the sense of promoting overall growth. Therefore, melatonin fits the description of being both an anti-stress promoter and a growth bio-stimulator in plants very well. Melatonin
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Approach Solution -2
Alternate approach - matching the mechanism to the description:
The description asks for a molecule doing two jobs at once: protecting the plant under stress, and actively promoting growth. Jasmonic acid mainly triggers defence signalling against pests, not broad growth promotion; 1-MCP simply blocks ethylene action to delay ripening, so it does not stimulate growth at all; Prohexadione-Ca blocks gibberellin synthesis, so it actively retards growth, the opposite of a bio-stimulator. Melatonin, by contrast, works as a powerful antioxidant that scavenges reactive oxygen species generated under drought, salinity, heat and cold stress, while separately promoting seed germination, root initiation and flowering, covering both halves of the definition simultaneously. Only melatonin satisfies both requirements together.
The description asks for a molecule doing two jobs at once: protecting the plant under stress, and actively promoting growth. Jasmonic acid mainly triggers defence signalling against pests, not broad growth promotion; 1-MCP simply blocks ethylene action to delay ripening, so it does not stimulate growth at all; Prohexadione-Ca blocks gibberellin synthesis, so it actively retards growth, the opposite of a bio-stimulator. Melatonin, by contrast, works as a powerful antioxidant that scavenges reactive oxygen species generated under drought, salinity, heat and cold stress, while separately promoting seed germination, root initiation and flowering, covering both halves of the definition simultaneously. Only melatonin satisfies both requirements together.
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