Acetylene, fruit ripening

Ethylene plays an essential role in the development of plants, for example in germination, growth and fruit ripening. Carbons 3 and 4 of methionine appear to be the most important source of the gas in vivo, but the effect is also induced by externally applied gas. Acetylene and carbon monoxide are competitive with ethylene. This suggests that a metal ion is present at the ethylene receptor site, a view confirmed by the inhibition of alkene binding by dithiocarbamate. The possibility that this metal is copper is supported by the preparation of copper(I)-monoalkene complexes that show the tight binding of monoalkenes characteristic of the ethylene receptor sites of plants. ... 

Helianthus annuus contain a pentaynene that disappears when the fruits begin to ripen. Although Centaurea seeds do not contain acetylenic compounds, 1-day-old seedlings do. The turnover time of many acetylenic compounds in plants is 6-48 h. The amount of polyacetylenes in plants ranges from traces to about 1%, but the amounts present often vary widely within and between plants. 

Ethylene is a natural ripening agent for fruit. Acetylene is a fuel used in welding torches. 

Alkenes are hydrocarbons that contain one or more carbon-to-carbon double bonds (C = C). Because double bonds are very reactive, they easily add hydrogen atoms (hydrogenation) or water (hydration) to the carbon atoms in the double bond. One important compound containing a double bond is ethene (ethylene), which is used to ripen fruit when ready for market. A common compound with a triple bond is ethyne (acetylene), which burns at high temperatures and is used in welding metals. 

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