What is Ethylene?

Ethylene is a chemical substance that has found a huge amount of applications for humans as well as nature. It is found in plants as an important hormone as well is used by humans to produce some of the important industrial products like polyethylene or polystyrene or even ethanol.

Ethylene as a Plant Hormone

Ethylene acts as a plant hormone that is gaseous in nature. It is the first known gas found to be a natural hormone. It helps the plant to get rid of old leaves by inhibiting growth and promoting their abscission or shredding, opening of flowers from the bud, ripening the fruits, etc. It is observed that when raw bananas are kept together with oranges, the bananas start showing premature ripening, this is due to the effect of ethylene hormone present in the oranges. This hormone was identified by Dimitry Neljubov in the year 1901 however, its use in agriculture dates back to ancient Egyptians and Chinese cultures.

Ethylene

The IUPAC name of ethylene is “ethene”, however, it is also known as “etileno” or “polyethylene”. It is a hydrocarbon gas (the simplest alkene) that is colorless, flammable, and has a faint sweet-musky odor. It has a carbon-carbon double bond and has the chemical formula H₂C=CH₂ or C₂H₄. It acts as a naturally occurring plant hormone as well as widely used in chemical industries. When hydrated it forms ethanol. Ethylene can be obtained from natural gas and petroleum also.

Structure of Ethylene

It is an ethane derivative in which both carbon atoms share a double bond between them. Each carbon is bound by two hydrogen atoms thus filling its valencies. It is a simple molecule with a 133.9 pm bond length of the carbon-carbon double bond and a 108.7 pm bond length of the carbon-hydrogen single bond having an inner angle of 121.3°. All the carbons and hydrogen of the ethylene lie in the same plane i.e. they are coplanar.

Commercial use of Ethylene

Following is the list of some common commercial uses of ethylene;

1. For the production of low-density polyethylene and high-density polyethylene.
2. As an anesthetic in surgery.
3. In metal welding.
4. In refrigeration.
5. Early ripening of fruits.
6. Curing agent for tobacco.
7. Manufacturing of alcohol.
8. As an herbicide.
9. As anti-refrigerant in car radiators.

Functions of Ethylene

Following is the list of some functions ethylene performs as a plant growth regulator;

1. Helps in the germination of seeds.
2. Helps in the ripening of the fruits.
3. Induces flowering from buds.
4. Helps in the determination of sex in flowers and produces female flowers in a male plant.
5. Helps in pollination.
6. Helps in root initiation and root growth.
7. Helps the flower in epinasty.
8. Effects gravitropism by reducing sensitivity to gravity.
9. Inhibits the longitudinal growth of the stem and promotes horizontal growth.
10. Promotes the senescence of leaves and flowers.
11. Promotes apical dominance.
12. Induces artificial ripening in climatic fruits.
13. Induces flowering in pineapple and mango.

FAQs on Ethylene

Q: Name some commercial materials which are obtained from ethylene.

Answer:

Some commercially important materials that are obtained from ethylene are; plastic or polythene, rubber, PVC (polyvinyl chloride), car glasses, etc.

Q: At what temperature petroleum or natural gas has to be heated to obtain ethylene?

Answer:

At 900°C petroleum or natural gas has to be heated to obtain ethylene industrially.

Q: Name some climatic fruits that require ethylene for their ripening.

Answer:

Some of the climatic fruits that require ethylene for their ripening are; banana, lemon, mango, avocado, kiwi, etc.

Q: Define plant growth regulator.

Answer:

Those chemical substances which are responsible for the regulation of plant’s growth and development are called plant growth regulators. These are also called plant growth hormones like ethylene, abscisic acids (ABA), auxins, gibberellins, and cytokinins.

Q: What are the two stages of ethylene synthesis?

Answer:

The two stages of the biochemical synthesis of ethylene in a plant are;

1. The compound S-adenosyl-L-methionine (SAM) is converted into 1-aminocyclopropane-1-carboxylic acid (ACC) by the action of the enzyme ACC synthase.
2. The ACC is then converted into ethylene by the action of the enzyme ACC oxidase.