Autoinhibition of Ethylene Production in Citrus Peel Discs

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Abstract
Wound ethylene formation induced in flavede tissue of citrus fruit (Citrus paradisi MacFad. cv. Ruby Red) by slicing was almost completely inhibited by exogenous ethylene. The inhibition lasted for at least 6 hours after removal of exogenous ethylene and was then gradually relieved. The extent of inhibition was dependent upon the concentration of ethylene (1 to 10 microliters/liter) and the duration of treatment. The increase in wound ethylene production in control discs was paralleled by an increase in 1-aminocyclopropane-1-carboxylic acid (AAC) content, whereas in ethylene-treated discs there was little increase in ACC content. Application of ACC completely restored ethylene production in ethylene-pretreated discs, indicating that the conversion of ACC to ethylene is not impaired by the presence of ethylene. Thus, autoinhibition of ethylene synthesis was exerted by reducing the availability of ACC. Ethylene treatment resulted in a decrease in extractable ACC synthase activity, but this decrease was too small to account for the marked inhibition of ACC formation. The data indicate that autoinhibition of ethylene production in citrus flavede discs results from suppression of ACC formation through repression of the synthesis of ACC synthase and inhibition of its activity.