We have cloned one member (PP-A CSI) of the 1-aminocyclopropane-1-carboxylate (ACC) synthase and two members (PP-ACO1 and PP-ACO2) of the ACC oxidase gene families in peach (Prunus persica L.) fruit and studied their expression characteristics during fruit ripening and treatment with CO(2) and 1-methylcyclopropene (MCP), inhibitors of ethylene action. Northern analysis showed that the abundance of PP-ACS1, PP-ACO1 and PP-ACO2 mRNAs increased with fruit ripening in parallel with increases in ethylene production and activities of ACC synthase and ACC oxidase. The abundance of PP-ACO2 mRNA was much lower than that of PP-ACO1. CO(2) and MCP treatment inhibited ethylene production, ACC synthase activity, and accumulation of PP-ACS1 mRNA. Although CO(2) had little effect on ACC oxidase activity, it inhibited the accumulation of PP-ACO1 and PP-ACO2 mRNAs to the same levels as MCP. Wound-induced ethylene production, ACC synthase activity, and the abundance of PP-ACS1 mRNA were blocked and stimulated by CO(2) and MCP, respectively. CO(2) and MCP had no effect on wound-induced ACC oxidase activity but inhibited the accumulation of its mRNA. Wound-induced activities of ACC synthase and ACC oxidase, and abundance of their mRNAs were inhibited and stimulated, respectively, by exogenous ethylene. The translational inhibitor, cycloheximide inhibited wound-induced ethylene biosynthesis but super-induced the accumulation of PP-ACS1 and PP-ACO1 mRNAs, suggesting that their induction is a primary response to the inducer. These results suggest that the expression of PP-ACS1 and PP-ACO1 genes play a key role in the regulation of ethylene biosynthesis in peach fruit during ripening and in response to wounding. The results also indicate that wound-induced PP-ACS1 and PP-ACO1 genes are under negative and positive control, respectively. Further, using MCP we provide evidence indicating that CO(2) does not regulate ACC synthase activity and expression of the PP-ACS1 gene in peach fruit during ripening and in response to wounding by antagonizing ethylene action. (C) 2001 Elsevier Science B.V. All rights reserved.