Limitations in the Use of Cycloheximide in Studies of Apple Ripening

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Abstract
In order to discover whethor the production of aroma volatiles by apple fruits is dependent on the synthesis of appropriate enzymes during ripening, excised peel, excised cortical tissue, and whole apples were treated with cycloheximide (CH). Volatile release, ethylene production, respiration, flesh softening, and peel chlorophyll degradation were measured. The ethylene and volatile compounds produced by excised peel apparently resulted from wounding rather than processes analogous to fruit ripening. Excised cortical tissue was capable of autonomous ripening with ethylene production, respiration, and softening comparable to that in intact fruits. After infiltration with sucrose solution the same changes occurred, but they were delayed by up to 4 d. Cycloheximide inhibited respiration although the extent of this inhibition decreased after 3 d. Cycloheximide prevented the onset of rapid ethylene production but stimulated production of ethanol, ethyl acetate, and other volatiles. Softening of CH-treated cortical discs was associated with progressive necrosis. When whole apples were infiltrated with CH through hypodermic needles inserted into the core, [14C]valine incorporation was inhibited from the core to the mid-cortex but not in the peel and outer cortex. Infiltration with sucrose solution delayed many ripening changes although the time of maximum [14C]valine incorporation was unaffected. Early effects of CH on respiration were masked by the effects of infiltration, but after 5 d CH-infiltrated fruit contained higher CO2 concentrations and respired more rapidly than controls. Internal ethylene concentrations were usually lower in CH-treated apples than in controls. CH stimulated release of ethanol and ethyl acetate but inhibited release of higher molecular weight esters such as propyl and butyl acetates. Cycloheximide-treated fruit softened, but this was apparently due to internal necrosis. Peel chlorophyll degradation was inhibited by CH treatment of whole apples although the tissue had apparently received no inhibitor.

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