Persimmon (Diospyros kaki Thunb.) fruit are usually classified as climacteric fruit; however, unlike typical climacteric fruits, persimmon fruit exhibit a unique characteristic in that the younger the stage of fruit detached, the greater the level of ethylene produced. To investigate ethylene induction mechanisms in detached young persimmon fruit, we cloned three cDNAs encoding 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (DK-ACS1, 2, and -3) and two encoding ACC oxidase (DK-ACO1 and -2) genes involved in ethylene biosynthesis, and we analyzed their expression in various fruit tissues. Ethylene production was induced within a few days of detachment in all fruit tissues tested, accompanied by temporally and spatially coordinated expression of all the DK-ACS and DK-ACO genes. In all tissues except the calyx, treatment with 1-methylcyclopropene, an inhibitor of ethylene action, suppressed ethylene production and ethylene biosynthesis-related gene expression. In the calyx, one ACC synthase gene (DK-ACS2) exhibited increased mRNA accumulation accompanied by a large quantity of ethylene production, and treatment of the fruit with 1-methylcyclopropene did not prevent either the accumulation of DK-ACS2 transcripts or ethylene induction. Furthermore, the alleviation of water loss from the fruit significantly delayed the onset of ethylene production and the expression of DK-ACS2 in the calyx. These results indicate that ethylene biosynthesis in detached young persimmon fruit is initially induced in calyx and is modulated by water loss through transcriptional activation of DK-ACS2. The ethylene produced in the calyx subsequently diffuses to other fruit tissues and acts as a secondary signal that stimulates autocatalytic ethylene biosynthesis in these tissues, leading to a burst of ethylene production.