Exposure to alcohol vapours reduces chilling-induced injury of excised cucumber cotyledons, but not of seedlings or excised hypocotyl segments

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Abstract
Cucumber (Cucumis sativus L. cv. Poinsett 76) seedlings with fully expanded cotyledons, and excised cotyledons, first true leaves, hypocotyl segments and fruit mesocarp discs were exposed to vapours from a series of aqueous alcohol solutions of 0 to 320 mM methanol, ethanol, n-propanol, n-butanol, and n-pentanol during chilling at 2.5°C for 5 d. Certain concentrations of each alcohol reduced subsequent chilling-induced ion leakage from the cotyledons and leaves. Exposure of cotyledons to certain methanol or ethanol solutions also reduced chilling-induced ethylene production, but not carbon dioxide production. In contrast, exposing cucumber seedlings with fully expanded cotyledons to the same series of alcohol concentrations that resulted in reduced chilling-induced ion leakage and ethylene production of excised cotyledons actually increased chilling injury of the seedlings. The hypocotyl region directly below the cotyledons was the site of chilling-induced injury and contained the most chilling-sensitive hypocotyl tissue. Exposing hypocotyl segments excised from this sensitive region to alcohol solutions did not significantly reduce chilling-inducedion leakage. Exposing excised cucumber cotyledons or hypocotyl segments to equivalent osmotic nonvolatile solutions of mannitol and glycerol at 2.5°C or to alcohol solutions at 12.5°C had no significant effect on the rate of ion leakage. For the series of alcohols used, the relationship between the log of the alcohol concentration that minimized chilling-induced ion leakage from cucumber cotyledon discs held at 2.5°C for 5 d and the log of the partition coefficient of the alcohol into olive oil or the log of the molecular weight of the alcohols was highly significant. The same concentrations of alcohols that reduced chilling-inducedion leakage also reduced stomatal aperture as measured as decreased porosity of excised cotyledons. The correlation between reduced chilling injury and stomatal conductance of cotyledons exposed to a series of ethanol solutions was highly significant. It appears that alcohols may reduce chilling injury of cucumber cotyledons by inducing stomata closure. Sufficient endogenously synthesized ethanol accumulated in discs held in N2 at 10°C for 1 d to confer tolerance to chilling at 2.5°C for 5 d.

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