Fruit Communication
Do you have any fruit around that you want to ripen faster? Well, just put it in a bag with a ripe banana and let the magic happen. This is something your grandma could probably tell you, and so could the ancient Egyptians, the people of ancient China, or farmers in the early 1900s.
Grandma likely stuck to the bag idea, but the Egyptians had a bit of a different strategy. They would keep great store rooms full of figs and would slash open a few, and boom, the whole bunch would ripen. The Chinese burned ritual incense in their store rooms to ripen their fruits, while American farmers in the early 20th century would burn kerosene lamps for the same purpose. Why did all of these different strategies work? It may seem logical that heat from the incense or the lamps would speed along the ripening process, but farmers figured out that warmth was not the culprit when they tried switching over from kerosene to electric heaters and their fruit didn’t ripen at all. And the heat hypothesis also leaves the fig slashing and banana bagging strategies up for question.
It took until 1924 for USDA researchers in California to take a closer look at why kerosene is an effective ripening agent. It turns out that when you burn kerosene, or Chinese incense for that matter, yes there is smoke, but there are also very small amounts of the molecule ethylene. Treating fruit with any amount of ethylene gas is enough to trigger the ripening process. After further investigation, it was discovered that ripe fruits also emit ethylene molecules and signal the fruit around them to ripen, hence the functionality of the banana bag and fig slashing tricks.
Why do plants do this? For reproductive purposes of course. The production of ethylene makes sure that all of the fruit on a single plant ripen simultaneously. When one pear begins to ripen, it “tells” its neighbors to do the same by the way of ethylene molecules. When fully fruited, a tree is much more attractive to passing herbivores who will kindly eat the fruit and disperse the seeds.
Source
Chamovitz, Daniel. What a Plant Knows: A Field Guide to the Senses. New York: Scientific American/Farrar, Straus and Giroux, 2012. Print.
