Synthesis of the phytohormone ethylene is believed to be essential for many plant developmental processes. The
control of ripening in climacteric fruits and vegetables is among the best characterized of these processes. One
approach to reduce ethylene synthesis in plants is metabolism of its immediate precurso’r, l-aminocyclopropane-lcarboxylic
acid (ACC). Soil bacteria containing an enzyme, ACC deaminase, were identified by their ability to grow
on ACC as a sole nitrogen source. The gene encoding ACC deaminase was cloned and introduced into tomato
plants. Reduction in ethylene synthesis in transgenic plants did not cause any apparent vegetative phenotypic
abnormalities. However, fruits from these plants exhibited significant delays in ripening, and the mature fruits
remained firm for at least 6 weeks longer than the nontransgenic control fruit. These results indicated that ACC
deaminase is useful for examining the role of ethylene in many developmental and stress-related processes in
plants as well as for extending the shelf life of fruits and vegetables whose ripening is mediated by ethylene.