Metabolism of 1-Aminocyclopropane-l-Carboxylic Acid during Apple Fruit Development

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Abstract
The metabolism of [U−14C] 1-aminocyclopropane-1-carboxylic acid (ACC) supplied to whole fruits of apple (Malus domestica Borkh., cv. Cox's Orange Pippin) was investigated. Radioactive ethylene was recovered in mercuric acetate traps and an acidic metabolite was formed in proportions which varied little with the absolute amount of substrate supplied. The amount of ACC usually supplied did not cause immediate, rapid ethylene production by mature, pre-climacteric fruit but the onset of production was earlier than in untreated fruit. The radioactive acidic metabolite was purified by four chromatographic procedures and activity was coincident with authentic 1-malonylamino) cyclopropane-1-carboxylic acid (MACC). The presence of this compound was confirmed by gas chromatography linked to mass spectrometry. MACC was a major metabolite of [14C] ACC supplied to apples throughout fruit development. The proportion converted to ethylene was low but increased with endogenous ethylene production in the final samples. MACC was shown to be a natural constituent of apple fruits and to accumulate to the amol kg−1 level.