Glutamine synthetase is the enzyme which catalyses the reaction of ammonia (NH3) and glutamic acid to form glutamine. Ammonia results from nitrate reduction, amino acid metabolism, and photorespiration. Glufosinate-ammonium inhibits the enzyme's activity. This leads to the accumulation of NH3 in the cell. As NH3 is strongly phytotoxic, the affected cells die. This is macroscopically manifested in necrotic spots and finally withering of plant.
Wilting of a treated mixed weed community may start within 24 hours in the tropics, or only after 8 days in cool continental spring or autumn temperatures.