Ethylene

Plants are sensible to smell and gases.

There is a gas produced by the plants called Ethylene. It is a natural plant hormone used to force the ripening of fruits.

Ethylene production is regulated by a variety of developmental and environmental factors. During the life of the plant, ethylene production is induced during certain stages of growth such as germination, ripening of fruits, abscission of leaves, and senescence of flowers. Ethylene production can also be induced by a variety of external aspects such as mechanical wounding, environmental stresses, and certain chemicals including auxin and other regulators.

What is actually caused by the gas may depend on the tissue affected as well as environmental conditions. In the evolution of plants, ethylene would simply be a message that was coopted for unrelated uses by plants during different periods of the evolutionary development.

List of plant responses to ethylene

• Seedling triple response, thickening and shortening of hypocotyl with pronounced apical hook.
• In pollination, when the pollen reaches the stigma, the precursor of the ethylene, ACC, is secreted to the petal, the ACC releases ethylene with ACC oxidase.
• Stimulates leaf and flower senescence
• Stimulates senescence of mature xylem cells in preparation for plant use
• Induces leaf abscission
• Induces seed germination
• Induces root hair growth — increasing the efficiency of water and mineral absorption
• Induces the growth of adventitious roots during flooding
• Stimulates epinasty — leaf petiole grows out, leaf hangs down and curls into itself
• Stimulates fruit ripening
• Induces a climacteric rise in respiration in some fruit which causes a release of additional ethylene.
• Affects gravitropism
• Stimulates nutational bending
• Inhibits stem growth and stimulates stem and cell broadening and lateral branch growth outside of seedling stage 
• Interference with auxin transport
• Inhibits shoot growth and stomatal closing except in some water plants or habitually flooded ones such as some rice varieties, where the opposite occurs
• Induces flowering in pineapples
• Inhibits short day induced flower initiation

In the prairies of North America the grass will use the ethylene to ensure their survival. When the buffallos are coming to the prairie and eating the grass it will create ethylene that will be taken downwind to tell the grass there that it has to produce seeds and put them to the ground to ensure that next year the seeds will grow again.

It is the same in a forest. The outside part of the forest will get the first cold weather of the winter season. The trees in the outside circle will turn their leaves into yellow and will generate ethylene to send the message to the inner trees that they have to turn their leaves colour in order to loose the leaves and not get frozen and die.

The ethylene will:

1. Ripen the apples, tomatoes, potatoes. Potatoes and apples should never be stored in the same room as the ethylene from the apple will cause the potatoes to sprout.
2. Make the grass produce seeds. The dandelion produces a lot of ethylene, that is why it is usually taken out in a garden to avoid the grass go seedly.

Polyethylene is a synthetic material. It has a similar structure as the ethylene, but it is not the solid form of ethylene.