The gas that acts as a plant hormone and promotes ripening in many tree fruits is ethylene.
Ethylene is a simple gaseous hydrocarbon that plants produce naturally in tiny amounts. In climacteric fruits such as apples, bananas, pears, and many mangoes, rising ethylene levels trigger coordinated changes: starches become sugars, tissues soften, colors shift, and characteristic aromas develop.
The gas also regulates other plant processes, including leaf shedding, flower aging, seed germination, and responses to flooding or physical injury. Because ethylene can spread through air, one ripening fruit may accelerate ripening in nearby fruit, especially in enclosed storage.
Ethylene was identified as a plant growth signal through observations of gas leaks and fruit storage. In 1934, British biologist Richard Gane demonstrated that ripe fruit produced ethylene and that the gas could induce ripening. Commercial facilities now use controlled ethylene exposure, while storage systems often remove or block it to extend shelf life.