Ethylene

Ethylene is a plant hormone that differs from other plant hormones in being a gas.

It has the molecular structure:

H₂C=CH₂

When fruits approach maturity, they release ethylene.

Ethylene promotes the ripening of fruit.

Among the many changes that ethylene causes is the destruction of chlorophyll. With the breakdown of chlorophyll, the red and/or yellow pigments in the cells of the fruit are unmasked and the fruit assumes its ripened color.

The presence of ethylene is probably detected by transmembrane receptors in the surface of the plasma membrane of the cells.

How the role of ethylene was discovered.

As is so often the case in science, the discovery of the role of ethylene was made by accident. When first harvested, lemons are often too green to be acceptable in the market. In order to hasten the development of a uniform yellow color, lemon growers used to store newly-harvested lemons in sheds kept warm with kerosene stoves. When one grower tried a more modern heating system, he found that his lemons no longer turned yellow on time. Following this clue, it was soon found that the important factor in the ripening process was not heat but the small amount of ethylene gas given off by the burning kerosene.