The action site of carbon dioxide in relation to inhibition of ethylene production in tomato fruit

High CO2 can inhibit ethylene production of various fruit. A high level of CO2 (20 kPa) was applied to tomato fruit (Lycopersicon esculentum Mill. cv Aromata) at 18 °C for 5 days. To investigate the primary action site of CO2, we used tomato fruit at a ripening stage where feedback regulation of ethylene production was of limited importance. Feedback reactions were further prevented by a treatment with 1-methylcyclopropene (1-MCP) before exposure to high CO2. Tomatoes with and without 1-MCP pre-treatment were exposed to 0 or 20 kPa CO2. Ethylene production, 1-aminocyclopropane-1-carboxylate (ACC) content and ACC oxidase mRNA abundance were measured after 1, 2 and 5 days exposure to 0 or 20 kPa CO2. High CO2-affected LE-ACO1, LE-ACO3 and LE-ACO4 transcripts differently. Several observations show that high CO2 did not affect the ethylene receptor: (1) CO2 had a much earlier and much stronger inhibitory effect on ethylene production than 1-MCP; (2) CO2 prevented while 1-MCP stimulated ACC accumulation; (3) CO2 prevented the 1-MCP induced decrease of LE-ACO1 abundance, and inhibited the 1-MCP induced decrease of LE-ACO3 abundance. Inhibition of ethylene production together with prevention of ACC accumulation by CO2, both in fruit with and without 1-MCP pre-treatment, points to inhibition at a site before the conversion of ACC to ethylene.