Regulation by Carbon Dioxide of Wound-induced Ethylene Biosynthesis in the Peel of Citrus Fruit

Abstract

The effect of carbon dioxide (CO2) on wound-induced ethylene biosynthesis in flavedo discs of mature orange fruits (Citrus sinensis L. Osbeck) is investigated. Wounding induced a marked and rapid increase on the rate of ethylene production, the content of 1-aminocyclopropane-1-carboxylic acid (ACC) and on the in vivo ACC oxidase (ACO) activity. Incubation of flavedo discs in a 15% CO2atmosphere suppressed activation of these processes. Wound-induced ethylene production was inhibited by CO2in a concentration-dependent manner but ACO activity was enhanced at concentrations between 1% and 5%. Kinetic analysis of the interaction between CO2and ACO activity indicated that high CO2acted as a noncompetitive inhibitor. Removal of CO2after 24 h incubation did not restore normal rates of ethylene production. CO2partially counteracted the increase in ethylene production and ACO activity induced by a pretreatment with an ethylene action inhibitor (STS, silver thiosulfate). This suggested that part of CO2action on ethylene biosynthesis might be due to interfering ethylene action. Collectively, the results indicated that ACS activity appeared to be the major regulatory step by which CO2suppresses wound-induced ethylene production. ACO was differentially modulated by CO2, which is being stimulated at low concentrations and inhibited at high concentrations.