Ethylene is a hormone found in a gaseous state. It is a simple hydrocarbon gas composed of two carbon atoms and four hydrogen atoms. Ethylene regulates many aspects of plant growth and development, including seed germination, leaf abscission, fruit ripening, and senescence. It is synthesized in response to various environmental and developmental signals, such as stress, wounding, and aging. Once produced, ethylene diffuses through the air and acts on target tissues, inducing a wide range of physiological and biochemical responses.