Also an unexpected and unusual plant hormone. Allegedly explains why when bananas were transported in vehicles with gas lamps (which gave off the gas) they ripened quicker. Since it is gaseous, fruits that use this molecule to ripen affect each other in a positive feedback sort of way. Produced by the fruit from a strange cyclic intermediate : 1-aminocyclopropane-1-carboxylic acid, which is made using SAM(S-adenosyl methionine). This decomposes to ethylene, catalyzed by an oxidase.

The Ethylene FAQ (really, frequently asked questions about ethylene?) says:

" Ethylene can promote ripening in tomatoes, bananas, citrus, pineapples, dates, persimmons, pears, apples, melons, mangos, avocados, papayas and jujubes"

Other C2H4 questions may be answered at