Involvement of Endogenous Ethylene in the Induction of Color Change in Shamouti Oranges

Abstract

Reducing the level of endogenous ethylene in detached Shamouti oranges (Citrus sinensis L. Osbeck) by means of subatmospheric pres-sure did not alter the rate of chlorophyll destruction and color changes during the first 8 days after harvest in the presence or absence of exogenous ethylene. Reducing the activity of ethylene by means of CO2-known to be a competitive inhibitor for ethylene -inhibited chlo-rophyll destruction and color change in Shamouti oranges ventilated with ethylene, but had no effect on these processes in the absence of applied ethylene. The evidence presented indicates that endogenous ethylene may not be the primary inducer for the natural color change in detached Shamouti oranges. Citrus fruits have generally been recognized as nonclimacteric fruit since an increase in respiration and ethylene production apparently does not occur after the mature fruit has been re-moved from the tree (1, 5). Orange fruits have been reported previously as not evolving ethylene (1), but the introduction of gas chromatographic techniques revealed measurable, although relatively small, concentrations of ethylene in both emanations and internal atmosphere of mature orange fruits (4). Prominent increases in both respiration and ethylene production have been noted when young citrus fruits are removed from the tree (2). Exogenously applied ethylene causes rapid degreening of cit-rus fruit rind (1). Ethylene not only enhances the destruction of Chi but also promotes the subsequent build up of carotenoids (1, 13). Relatively high concentrations of ethylene are required for half-maximal color change response as compared with other ethylene-induced phenomena (1). In addition, exogenous