Ethylene differs from other plant hormones because it is:
Ethylene stands unique among classical phytohormones being only gaseous hydrocarbon C2H4 with high diffusivity without need for active transport proteins. Biosynthesis follows methionine to S-adenosyl methionine AdoMet then ACC via ACC synthase ACS multigene family rate limiting, finally oxidation to ethylene by ACC oxidase ACO requiring iron ascorbate oxygen. As volatile it accumulates in sealed culture vessels influencing morphogenesis unless vented. Signaling occurs at endoplasmic reticulum membrane where receptors ETR1, ERS1, ETR2 function as negative regulators; in absence of ethylene the
Ref: Bleecker & Kende Annu Rev Cell Dev Biol 2000 ethylene; NCBI NBK21448 ethylene.
