A role for cyanide, derived from ethylene biosynthesis, in the development of stress symptoms

Cyanide is formed as a co‐product of ethylene during the oxidation of 1‐aminocyclo‐propane‐1‐carboxylic acid (ACC) catalyzed by ACC oxidase. A toxic or regulatory function for cyanide in plant metabolism remains controversial. However, recent studies on the mode of action of auxin herbicides in sensitive plants suggest that the accumulation of tissue cyanide, derived ultimately from herbicide‐stimulated ACC synthesis, is implicated in the induction of herbicide phytotoxicity. Furthermore, increases in cyanide levels have been observed during the formation of necrotic lesions in tobacco mosaic virus‐infected tobacco leaves. It thus appears worthwhile to elucidate in more detail a possible role for cyanide in the induction of cell death under stress conditions which coincide with a strong stimulation of ethylene biosynthesis.