Inhibition of Photosynthesis in Barley ( Hordeum vulgare L.) Leaves by Phosphinothricin (Glufosinate). Short and Long-Term Effects

Several inhibitors of the GS (Methionine sulphoximine, MSO; Phosphinothricin, PPT) have been used in studies of the role of this key and the mechanism of its action. Both substances can inhibit GS “in vivo”, cause a dramatic increase of ammonia and inhibit the rate of photosynthetic CO2 uptake. Initially it was thought that the build-up of ammonia was the cause of photosynthetic inhibition; however, Sauer et al. (1987) postulated that aminoacid metabolism, disturbed by PPT, results in; a) Inhibition of synthesis of proteins,e.g. the QB protein causing eventually the collapse of electron transport; b) Toxic accumulation of glyoxylate, an inhibitor of Rubisco c) Depletion of the pool of intermediates of the RPPP via hidroxipiruvate derived from peroxisomal serine transamination.