Ethylene biosynthesis in relation to cyanide metabolism

Cyanide is a co-product of ethylene biosynthesis in higher plants via the ACC pathway. In certain physiological states, such as fruit ripening and flower senescence, and in many environmental conditions, such as flooding and chilling, ethylene biosynthesis is greatly induced. Cyanide is toxic to plants if it accumulates in plant tissues; however, during fruit ripening, the co-product cyanide is shown to be rapidly conjugated to form L-3-cyanoalanine derivatives by the enzyme L-3-cyanoalanine synthase. Recent evidence shows that cyanide, the coproduct of ethylene biosynthesis, causes phytotoxic effects on plants subjected to auxin-type herbicide treatments. It points to the possibility that under certain severe stress conditions, the induced ethylene, and thereby cyanide, may cause the death of the plants.