DC-ACS1 is a gene for 1-aminocyclopropane-1-carboxylate (ACC) synthase which is expressed slightly in the gynoecium, but abundantly in petals of carnation (Dianthus caryophyllus L.) flowers. It is known that ethylene evolved from the gynoecium triggers the expression of DC-ACS1 and DC-ACO1 (the gene for carnation ACC oxidase), which results in an abundant ethylene production in petals. In a transgenic carnation (16-0-66 line) transformed with DC-ACS1 cDNA in sense orientation, the exogenous ethylene treatment caused the expression of DC-ACO1 in the gynoecium and petals, but not that of DC-ACS1. This suggests that the cosuppression of the expression of endogenous DC-ACS1 gene by the integrated transgene. DC-ACS1 transcript is absent in both gynoecium and petals of senescing 16-0-66 flowers, so that the flowers produce no ethylene; whereas DC-ACO1 transcript is present in the gynoecium but absent in the petals. These findings give further support on the role of the DC-ACS1 gene in the gynoecium for ethylene production by petals in senescing carnation flowers.