Effects of high carbon dioxide exposure on ethylene biosynthesis in peach and tomato fruits

Ethylene production, oxygen uptake, the activities of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase in vivo and the contents of ACC and 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC) were determined in peach and tomato fruits held in carbon dioxide-enriched atmosphere. Ethylene production in peaches decreased to a trace level with 60% carbon dioxide and in tomatoes to 50% of the initial level. The ethylene production rates in both fruits reverted to the initial level when the fruits were transferred back to air. Oxygen uptake in both fruits was markedly inhibited during carbon dioxide exposure. In vivo activities of ACC oxidase and ACC synthase in both fruits were also inhibited during carbon dioxide exposure. ACC content in peaches held in carbon dioxide-enriched atmosphere decreased but it increased in tomatoes. The level of MACC in peaches was constant during carbon dioxide treatment, whereas that in tomatoes slightly increased. These results indicate that inhibition in ethylene production by carbon dioxide may be mediated mainly by reduced conversion of ACC to ethylene in tomatoes, whereas in peaches, the inhibition is attributed to both reduced conversion of S-adenosylmethionine to ACC and ACC to ethylene.