Figure 1.

Schematic overview of ethylene synthesis intermediates (S-adenosyl-methionine, SAM; 1-aminocyclopropane-1-carboxylic acid, ACC) and enzymes (ACC synthase, ACC oxidase). The formation of nitric oxide through putrescine (PUT) oxidation by copper-amine-oxidase (CuAO) is also depicted; however, the question mark indicates that this mechanism requires further experimental evidence. Additional abbreviations: L-Met, L-methionine; SAMDC, SAM decarboxylase; dcSAM, decarboxylated SAM, SPD, spermidine; SpdS, spermidine synthase; SPM, spermine; SpmS, spermine synthase.