Q.46 The role of ethylene in plants is:
1. senescence of leaves and ripining of fruits
2. cell division
3. inhibition of root growth
4. production of tuber and bulb formation
Ethylene primarily promotes leaf senescence and fruit ripening, distinguishing it from other plant hormones like auxins or cytokinins. This matches option 1 precisely, while other options describe secondary or hormone-specific effects.
Correct Answer
Option 1: senescence of leaves and ripening of fruits
Ethylene, the gaseous plant hormone, triggers climacteric ripening in fruits (banana, tomato, apple) via autocatalytic production and induces programmed leaf senescence by degrading chlorophyll and activating cell wall hydrolases. These are its signature functions in plant physiology textbooks.
Ethylene’s Primary Roles
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Fruit Ripening: ↑ pectinase, cellulase → fruit softening; ↑ amylase → starch → sugar
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Leaf Senescence: Chloroplast breakdown → yellowing; ↑ protease activity
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Abscission: Leaf/fruit drop via cell wall dissolution at abscission zone
Options Analysis
| Option | Statement | Correct? | Explanation |
|---|---|---|---|
| 1 | Senescence of leaves and ripening of fruits | ✅ | Primary, defining functions – banana ripening, autumn leaf drop |
| 2 | Cell division | ❌ | Cytokinin primary; ethylene may inhibit in some contexts |
| 3 | Inhibition of root growth | ❌ | Secondary effect; auxins primary for root inhibition |
| 4 | Production of tuber and bulb formation | ❌ | Gibberellins primary; ethylene may promote dormancy break |
Detailed Function Breakdown
Primary Functions (Option 1)
Leaf Senescence Pathway:
Ethylene → ↑ ACC synthase → ↑ ethylene receptors →
↓ chlorophyll synthesis + ↑ chlorophyllase → Yellowing
Fruit Ripening Cascade:
Ethylene → Respiratory climacteric →
↑ Polygalacturonase + ↑ Amylase → Softening + Sweetening
Why Other Options Fail
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Cell Division: Cytokinin:SA ratio controls; ethylene stress response only
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Root Growth: IAA transport inhibition (indirect); gravity/auxin primary
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Tuber/Bulb: GA → ↑ internode; ethylene breaks dormancy (not formation)
Exam Memory Aid
“Ethylene = ENDINGS”
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End of leaf life (senescence)
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Ripening (fruit)
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Intercalary growth (grasses)
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Nectar production
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Gynoecium development
Common Traps
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Triple Response (seedling etiolation) confused with primary functions
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Stress hormone role (flooding, wounding) mixed with development
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Auxin crosstalk mistaken for primary function
Pro Tip: NEET emphasizes fruit ripening + senescence as ethylene’s hallmark. Ignore secondary/stress effects for MCQs.
