It is the main organic sulfur molecule. Precursor of the synthesis of methionine, glutathione (main antioxidant of plants), vitamins, cofactors and compounds that are part of the defensive system of plants (glucosinolates, thionines and phytoalexins). Cysteine is a crucial metabolite in the plant’s defense system.

In addition, some studies relate tolerance to stress situations caused by heavy metals (Zn and Cd) with the accumulation of cysteine in plants.