Ethylene has profound effects on many developmental events and environmental responses of plants (Yang and Hoffman, 1984). Endogenous production of ethylene increases during certain stages of growth and development, such as seed germination, fruit ripening, and leaf and flower senescence and abscission, and in response to drought, flooding, physical wounding, chilling injury, pathogen infection, and chemical inducers (Yang and Hoffman, 1984; Theologis, 1992). In higher plants, ethylene is biosynthesized from Met by a well-defined pathway in which 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase catalyze the reactions from S-adenosylmethionine to ACC and ACC to ethylene, respectively (Yang, 1987). With advancement in molecular biology techniques, cDNA and genomic clones for both enzymes have been isolated from various plant species, and both enzymes appear to be encoded by multigene families. Using these cDNA clones, expression of individual members has been characterized in different tissues and in response to specific stimuli known to induce ethylene biosynthesis (Kende, 1993; Zarembinski and Theologis, 1994; Fluhr and Mattoo, 1996).