Ethylene and Fruit Ripening
Summary
Ripe fruit gives off ethylene, a gaseous plant hormone that speeds the ripening of nearby fruit and wilts flowers. You’ll be able to explain why a gas makes a good signalling molecule, why “one bad apple spoils the bunch” is literally true, and how temperature and blocking agents control the effect.
History
Ethylene’s role in plant biology was discovered accidentally. In the early 1900s, farmers noticed that fruit stored near kerosene heaters ripened faster. Russian scientist Dmitry Neljubow identified ethylene as the culprit in 1901, and in 1934, R. Gane confirmed that plants themselves produce ethylene.
This tiny molecule (C₂H₄) turned out to be a major plant hormone - the only gaseous hormone known in plants. It regulates ripening, flowering, leaf drop, and stress responses. The discovery revolutionized the fruit industry: today, bananas are shipped green and ripened on demand with ethylene gas, while apples are stored in low-ethylene environments to stay fresh for months.
The same hormone that ripens fruit also signals flowers to wilt and die - a response that makes biological sense (after pollination, petals are no longer needed) but frustrates florists and flower lovers.
Hazards & preparation
PPE: none — this is a fully food-safe, low-hazard observation.
- Don’t seal the bags airtight; fold them loosely so a little air exchange remains.
- Wash the fruit before eating it afterward (it’s fine to eat).
Disposal: compost or bin the fruit and flowers when done. See the Safety page.
Materials
- Ripe banana (or apple) - 1
- Green bananas or unripe tomatoes - 2-4
- Fresh cut flowers (carnations work well) - 2-4 stems
- Paper bags - 3
- Glass jars or containers with lids - optional
Procedure
Part A: Accelerated ripening
- Place one green banana in a paper bag with a ripe banana.
- Place another green banana in a paper bag alone (control).
- Leave a third green banana in open air (second control).
- Fold the bags closed loosely (not airtight).
- Check daily — the banana with the ripe companion ripens 2-3 days faster.
Part B: Flower wilting
- Place one fresh flower in a jar or bag with a ripe banana.
- Place another flower in a bag alone (control).
- Keep a third flower in a vase with water (second control).
- Observe over 24-48 hours — the flower with the banana wilts dramatically faster.
What you should see
Over a few days the bagged banana beside the ripe one yellows and spots noticeably ahead of both controls — the trapped ethylene doing its work. In the flower test, the bloom sharing a jar with the banana droops and browns within a day or two while the controls stay fresh.
| Symptom | Likely cause | Fix |
|---|---|---|
| No difference between bags | Bags too open, ethylene escaped | Fold bags more closed (still not airtight); use a riper “source” fruit |
| Everything ripens fast | Room too warm | Keep all samples at the same, cooler temperature for a fair test |
| Flower doesn’t wilt faster | Weak ethylene source | Use a very ripe banana or apple; enclose more snugly |
The Science
Ethylene (C₂H₄) is a gaseous plant hormone:
| Effect | Mechanism |
|---|---|
| Fruit ripening | Breaks down cell walls, converts starch to sugar, develops color and aroma |
| Flower wilting | Triggers senescence (aging), causes petal drop |
| Leaf yellowing | Breaks down chlorophyll |
High ethylene producers include ripe bananas, apples, avocados, tomatoes, and damaged or stressed fruit. Ethylene-sensitive items include unripe fruit (ripens faster), cut flowers (wilt faster), and leafy vegetables (yellow). This is why you store bananas away from other fruit unless you want them to ripen, keep flowers away from the fruit bowl, and store apples separately.
Questions to Explore
Why is ethylene a gas? Most plant hormones are large water-soluble molecules; ethylene is a tiny gas. What advantage does a gaseous hormone have for coordinating ripening?
Hint / answer
As a gas, ethylene spreads on its own through air spaces and reaches every part of a fruit — and neighbouring fruit — without needing to be carried in sap. That makes it ideal for broadcasting a “ripen now” signal quickly and evenly.
Why does a ripe fruit speed ripening of unripe ones? Ripening makes more ethylene — a feedback loop. Why evolve that?
Hint / answer
The self-amplifying loop makes a whole fruit (and a whole tree’s crop) ripen together and fast, presenting a big, obvious, sweet reward that attracts seed-dispersing animals at just the right moment. Coordinated ripening improves the odds the seeds get spread.
Why do refrigerators slow ripening? Cold delays the effect. Does it slow ethylene production, the response, or both?
Hint / answer
Both. Cold slows the enzyme reactions that make ethylene and those that respond to it, since enzyme-driven processes generally slow with temperature. So chilling both cuts the signal and mutes the reaction — keeping fruit fresh longer.
What stops a wilted flower from recovering? It won’t revive in fresh air. Is the response reversible, unlike ripening?
Hint / answer
Ethylene triggers senescence — the flower actively dismantles its own cells (programmed death), which can’t be undone by removing the gas. Ripening changes are also one-way, but wilting is outright cell death, so the petals can’t be restored.
How do commercial growers control this? Bananas shipped green, gassed later. What if a fruit’s ethylene behaviour differs a lot?
Hint / answer
Growers pick and ship in low-ethylene, cool, controlled atmospheres, then dose ethylene to ripen on schedule. A fruit that ripens on the plant or barely responds to ethylene (like some berries or citrus) can’t be handled this way — it must be picked ripe, so it ships and stores poorly.
Going further
- Rank the emitters. Test which “source” fruit (apple, banana, tomato) ripens a green banana fastest — a rough ethylene-output ranking.
- Track it by weight. Weigh the fruit daily to follow ripening and water loss quantitatively.
- Try to block it. Compare a snug bag with a slightly vented one to see how removing ethylene slows the effect (the principle behind commercial 1-MCP treatment).