A ripe banana really can ripen the fruit beside it. The culprit is a gas.
Ripening fruit gives off ethylene, the simplest of plant hormones and the first gas known to act as one. Traces of it trigger ripening in neighbouring fruit, open flowers and drop leaves. Ancient Egyptians gashed figs to speed ripening; they were unknowingly releasing it.
Ethylene is a tiny hydrocarbon molecule, two carbon atoms and four hydrogens, produced by almost every part of a plant. At trace levels it regulates the ripening of fruit, the opening of flowers and the shedding of leaves. In some water plants, including rice, it drives rapid stem growth to escape rising floodwater. Wounding, drought, chilling and disease all increase its production.
People exploited it long before they understood it. Ancient Egyptians slashed figs to hasten ripening, since wounding stimulates ethylene. The ancient Chinese burned incense in closed rooms to ripen pears. In the 19th century, city dwellers noticed that leaking gas from street lamps stunted plants, killed flowers and made leaves fall early, and in 1874 smoke was found to make pineapple fields bloom. In 1901 the Russian botanist Dimitry Neljubow identified ethylene as the component of illuminating gas that affected peas.
Florida farmers ripened crops in sheds warmed by kerosene lamps, crediting the heat. In 1924 Frank Denny showed it was the ethylene the lamps gave off: as little as one part per million turned green lemons yellow in six to ten days. In 1934 the British biologist Richard Gane found that ripe fruit makes ethylene itself, remarking on its prodigious power in such small amounts; a single apple might release roughly a cubic centimetre over its life. In some fruit, ethylene triggers a burst of respiration that releases still more ethylene, so ripening feeds on itself.
The practical lessons follow. Commercial ripening rooms gas bananas and other fruit with controlled doses. Pineapple and other bromeliad growers induce flowering with ethylene, sometimes simply by enclosing the plant with a banana peel. On the other hand, the gas shortens the life of many fruits and cut flowers, and stressed flowers in transit produce more of it, a significant cost for florists. Keeping ripening fruit away from flowers, and from produce you want to keep, is sound advice.
Source: Wikipedia — Ethylene (plant hormone) · Text summarised from Wikipedia (CC BY-SA 4.0)
