Ethylene
Long before its role as a plant hormone was appreciated, the simple hydrocarbon ethylene was known to defoliate plants when it leaked from gaslight in street lamps, But ethylene is a natural product of plant metabolism and appears to be the main factor in the formation of specialized layers of cells that precedes the dropping off of leaves from plants, We have already mentioned the way in which auxin, diffusing down from the spical meristem of the stem, may stimulate the production of ethylene in the tissues around the lateral buds and thus retard their growth. Ethylene also suppresses stem and root elongation, probably for similar reasons.
Ethylene is also produced in large quantities during a certain phase of the ripening of fruits, when their respiration is proceeding at its most rapid rate, At this phase of ripening, complex carbohydrates are broken down into simple sugars, cell walls become soft, and the volatile compounds associated with flavor and scent in the ripe fruits are produced, When ethylene is applied to fruits, it hastens their ripening. One of the first lines of evidence that led to the recognition of ethylene as a plant hormone was the observation that gases that came from oranges caused premature ripening in bananas. Such relationships have led to major commercial uses. Tomatoes are often picked green and then artificially ripened as desired by the application of ethylene. Ethylene is widely used to speed the ripening of lemons and oranges as well. Carbon dioxide produces effects in fruits opposite to those of ethylene, and fruits that are being shipped are often kept in an atmosphere of carbon dioxide if they are not intended to ripen yet.
แหล่งข้อมูล: Understanding Biology. Page 728.
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