Ethylene: The Gaseous Plant Hormone for Ripening Fruits

Ethylene is a simple gaseous plant hormone with formula C2H4. Unlike other hormones that move through tissues in liquid form, ethylene spreads as a gas through air spaces inside the plant and even to neighbouring fruits. It mainly promotes ripening and ageing.

Ethylene matters in the fruit industry because one ripe fruit can speed ripening of many others. Controlling ethylene allows bananas, mangoes, and tomatoes to be transported green and ripened on demand near markets.

Key Concepts

Ethylene: A gaseous hydrocarbon hormone that promotes fruit ripening, senescence, and abscission.

Climacteric fruits: Fruits like banana, mango, apple, and tomato that show a rise in respiration and ethylene during ripening.

Abscission: Shedding of leaves, flowers, or fruits from the plant.

Senescence: Ageing process in leaves and flowers leading to yellowing and death.

Ethephon: A synthetic compound that releases ethylene when applied to plants.

Ethylene effects can occur at very low concentrations, often below 1 part per million in air.

How It Works

1. Ethylene is produced from methionine amino acid in plant tissues, especially ripening fruits and stressed tissues.
2. As a gas, it diffuses out of cells and through intercellular spaces.
3. It binds to receptors in target cells and switches on ripening genes.
4. Enzymes soften fruit walls, convert starch to sugars, and produce colour and aroma compounds.
5. Ripening fruit produces more ethylene, creating a positive feedback loop.
6. Nearby fruits exposed to the gas also start ripening.

Worked Example

A trader places 100 green bananas in a chamber. Ten ripe bananas releasing ethylene are added. After 2 days, 85 bananas turn yellow. Ripening percentage with ethylene source is 85 divided by 100 multiplied by 100 equals 85 percent. In a control chamber without ripe bananas, only 15 turn yellow in the same time, which is 15 percent. Difference is 70 percentage points. The calculation shows how ethylene from a small source triggers large scale ripening.

Common Misconceptions

• Ethylene is harmful and artificial only. Plants naturally produce it, and it is essential for normal ripening and leaf fall.
• All fruits ripen better after picking. Non-climacteric fruits like grapes and citrus do not ripen much after harvest.
• Keeping fruits in a closed bag always causes spoilage. It traps ethylene and speeds ripening, which is useful if monitored, but over ripening can follow.

Real-World Applications

Ethephon is used to induce uniform ripening and flowering in pineapple. Ethylene scrubbers and controlled atmosphere storage slow ripening during long transport. Fruit sellers use calcium carbide in some places, which is unsafe and banned in many regions, while regulated ethylene chambers are safer. Removing ethylene delays senescence of cut flowers.

Ethylene turns ripening into a coordinated, airborne signal. Managed well, it reduces waste and delivers fruits at perfect maturity. Left uncontrolled, it causes rapid over ripening and loss.