Carbon Dioxide Enhances the Development of the Ethylene Forming Enzyme in Tobacco Leaf Discs

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Abstract
Since CO2 is known to stimulate ethylene production by promoting the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene, the effect of CO2 on the activity and the development of the ethylene forming enzyme (EFE) was studied in tobacco (Nicotiana tabacum L. cv Havana 425 and Xanthi) leaf discs. In addition to previous observations that EFE activity is dependent on CO2 concentration and is saturable with 2% CO2, present data show two saturation curves at 2% and 10% CO2. Promotion of EFE development was dependent also on CO2 concentration (saturated at 2% CO2) and duration (maximum at 24 in the dark), and was abolished by 20 micromolar cycloheximide. Application of exogenous ethylene (20 microliters per liter) or light treatment further increased the CO2-enhanced development of EFE, implying that these two factors can also affect EFE development via interaction with CO2. The results suggest that CO2 exerts its stimulatory effect on the conversion of ACC to ethylene by enhancing not only the activity but also the synthesis of EFE in leaf discs.