Ethylene: The Ripening Hormone
Imagine you've bought a bunch of raw bananas. You put them in a paper bag with a ripe apple. The next day, the bananas are noticeably yellower. What happened? The apple released a gas that told the bananas, "It's time to ripen." That gas is ethylene.
Ethylene is the only gaseous plant growth regulator (PGR). It's a simple hydrocarbon — just two carbons and four hydrogens (C2H4) — but its effects are dramatic. Unlike auxins or gibberellins that promote growth, ethylene is largely about finishing things: ripening, aging, and shedding.
The Precise Statement
Ethylene is a gaseous plant hormone that regulates fruit ripening, senescence (aging), abscission (dropping of leaves/fruits), and epinasty (downward curling of leaves). It is produced naturally by most plant tissues, especially in response to stress, wounding, or during ripening.
Key Effects Explained
Fruit Ripening — This is ethylene's most famous job. Unripe fruits produce a little ethylene, which triggers more ethylene production in nearby fruits (a positive feedback loop). That's why one rotten apple spoils the barrel — the rotten one releases ethylene that ripens (and then rots) the others. Commercially, fruits like mangoes and tomatoes are picked green, transported, then exposed to ethylene gas in ripening chambers.
Senescence and Abscission — Ethylene accelerates aging. It breaks down chlorophyll (yellowing leaves), weakens cell walls at the abscission zone (where a leaf or fruit attaches to the stem), and promotes dropping. This is why ethylene is used to defoliate cotton plants before mechanical harvesting.
Epinasty — When a plant is flooded or stressed, ethylene causes the upper side of leaf petioles to grow faster than the lower side, making leaves curl downward. This is a visible sign of stress.
A common mistake is thinking ethylene only ripens fruits. It also promotes senescence, abscission, and epinasty — and in some cases (like pineapple flowering) it even promotes flowering.
Practical Applications
- Ripening chambers: Expose unripe fruits to ethylene gas
- Defoliation: Spray ethylene-releasing compounds (like ethephon) on cotton
- Shelf-life control: Remove ethylene from storage rooms (using potassium permanganate scrubbers) to keep fruits fresh longer
Ethephon (C2H6ClO3P) is a synthetic compound that breaks down inside plant tissues to release ethylene. It's sprayed as a liquid but acts as a gas inside the plant — clever chemistry.
Ethylene: the gaseous hormone that tells plants when to finish — ripen, age, and let go.
Students revising Plant Growth and Development for their CBSE Class 11 Biology exam, or preparing for NEET Biology, often search 'Ethylene: Definition & Diagram' or 'Ethylene previous year questions' - this topic is fully aligned with the NCERT Class 11 Biology curriculum. The role of ethylene in fruit ripening is also relevant to post-harvest technology, an applied topic occasionally tested in board exams.