Ethylene - Plant Hormones
Amongst hormones in both plant and animal kingdoms, ethylene, a gaseous hydrocarbon, is unique. Despite its chemical simplicity, it is a potent growth regulator. Even twenty years ago, there was a dispute whether this gas, which had been shown to have a range of multiple effects on plant tissues could be properly called a hormone. Ethylene can be smelt in ripening fruits, as it is involved in the ripening process.
Ethylene gas hastens fruit ripening, and as fruit ripens, it produces even more ethylene gas. It is production of ethylene gas by overripe fruits that explains why one rotten apple can spoil the whole basket. Stimulation of fruit ripening by ethylene has been commercially exploited by shipping tomatoes, bananas, oranges, mangoes and many other fruits when green, in ventilated crates (to prevent accumulation of ethylene) and then gased with ethylene before distributing to consumer. Ethylene may also help in determining sex in certain flowers. Along with gibberellin ethylene controls the ratio of male to female flowers. Ethylene treatment ensures higher ratio of female flowers in some monoecious plants such as cucumber. Therefore, ethylene is widely used in green houses to increase the yield of cucumber by inducing the production of female flowers. Silver nitrate is an antagonist of ethylene. It induces the formation of male flowers.