Ethylene

Ethylene (IUPAC name: ethene) is a gaseous organic compound with the formula C₂H₄. It is the simplest alkene, Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone.

Structure and Bonding

This hydrocarbon has four hydrogen atoms bound to a pair of carbon atoms that are connected by a double bond. All six atoms that comprise ethylene are coplanar. The H-C-H angle is 119°, close to the 120° for ideal sp² hybridized carbon. The molecule is also relatively rigid: rotation about the C-C bond is a high energy process that requires breaking the π-bond.

The π-bond in the ethylene molecule is responsible for its useful reactivity. The double bond is a region of high electron density, thus it is susceptible to attack by electrophiles. Many reactions of ethylene are catalyzed by transition metals, which bind transiently to the ethylene using both the π and π* orbitals.

Ethylene as a plant hormone

Ethylene serves as a hormone in plants. It acts at trace levels throughout the life of the plant by stimulating or regulating the ripening of fruit, the opening of flowers, and the abscission (or shedding) of leaves. Commercial ripening rooms use "catalytic generators", to make ethylene gas, from a liquid supply of ethanol. Typically, a gassing level of 500 ppm to 2,000 ppm is used, for 24 to 48 hours. Care must be taken to control carbon dioxide levels in ripening rooms when gassing, as high temperature ripening (68F) has been seen to produce CO2 levels of 10% in 24 hours.

Ethylene perception in plants

Ethylene could be perceived by a transmembrane protein dimer complex. The gene encoding an ethylene receptor has been cloned in Arabidopsis thaliana and then in tomato. Ethylene receptors are encoded by multiple genes in the Arabidopsis and tomato genomes. The gene family comprises five receptors in Arabidopsis and at least six in tomato, most of which have been shown to bind ethylene. DNA sequences for ethylene receptors have also been identified in many other plant species and an ethylene binding protein has even been identified in Cyanobacteria.

Ripe fruit will produce ethylene gas and can make a fruit not yet ripe into ripe due to it gases.

Experienced during the ripening of fruit, then the existing tissue in the fruit increased production of ethylene gases. so each fruit has a ethylene gas but the gas was increased along with the ripe fruit.

Not yet ripe fruit can be ripe because the fruit ripening ethylene gas stimulated by that diffuses into the intercellular spaces of the fruit. Gas can also diffuse through the air from one fruit to another fruit, fruit will mature more quickly if the fruit is stored in a plastic bag which resulted in accumulated ethylene gas.