Studies on the mechanism of herbicidal action of N‐(Phosphonomethyl) glycine*

Abstract

Summary:Application of N‐(phosphonomethyl) glycine or GLY'PHO‐SATE to couch grass Pancum repens (L) Beauv. resulted in an intitial increase of the total amino acid content in the plant. which reached a maximum on the 8th day following treatment This was most marked in the rhizomes where the value was about three times that of the control plants. The initial increase fell off rapidly with time and on the 15th day after application the total amino acid content of the treated leaf and rhizome samples was less than the controls Resurgence of rhizome activity was noticeable on about the 48th day (viz. 7 weeks after t he Ist application).

Effect of Glyphosate on Aromatic Amino Acid Metabolism in Purple Nutsedge (Cyperus rotundus)1

“…Although treated and untreated tubers were not different at 3 DAT, by 5 DAT the total free amino acids of glyphosate treated tubers were higher than control tubers (Figure 2). Ekanayake et al (1979) observed that application of glyphosate to torpedograss (Panicum repens L.) resulted in an initial increase of the total amino acid concentration in the plant, which reached a maximum at 8 DAT. In addition, Tymonko (1979) reported a 38% increase of total free amino acids 1 DAT with glyphosate in isolated soybean leaf cells.…”

“…Shaner and Lyon (1979) also indicated that the endogenous levels of tyrosine and phenylalanine decreased by 50% 6 h after the beginning of the glyphosate treatment while the levels of other amino acids increased. An increase in the total free amino acid concentration in treated plants also has been reported (Ekanayake et al 1979). Glyphosate increased extractable phenylalanine ammonia-lyase activity, which could partially explain the reduced pools of phenylalanine and tyrosine, and cause accumulation of toxic levels of ammonia and phenolic acid (Hoagland 1981).…”

Effects of Glyphosate on Metabolism of Phenolic Compounds: VI. Effects of Glyphosine and Glyphosate Metabolites on Phenylalanine Ammonia-Lyase Activity, Growth, and Protein, Chlorophyll, and Anthocyanin Levels in Soybean (Glycine max) Seedlings

“…Glyphosate does affect protein content in older soybean plants where protein decreased after 30 h in the first trifoliate but increased in unifoliate leaves at 54 to 78 h 4 . Electrophoretic studies of control and glyphosate- (13). Gly phosine decreases the 70-S ribosome fraction (chloroplastic ribosomes) in maize and modifies total fraction I protein (7).…”

Effects of Glyphosate on the Metabolism of Phenolic Compounds: VII. Root-Fed Amino Acids and Glyphosate Toxicity in Soybean (Glycine max) Seedlings

“…The mechanism of action of the non -specific herbicide, glyphosate, is thought to be intimately associated with the metabolism of aromatic amino acids (10,11,14,15,18,20,21,24). Recent work has shown that glyphosate inhibits aromatic amino acid synthesis by inhibiting synthesis of 5-enolpyruvylshikimate-3-phosphate (1,2,22,34).…”

“…Glyphosate-reduced growth of carrot cell cultures was reversed by feeding aspartate, glutamate, and certain tricarboxylic acid cycle acids individually or in combination (25). Although glyphosate reduces free pools of aromatic amino acids in intact higher plants (11,14,20,21,28,32), increasing phenylalanine levels to those of control plants with the potent, specific inhibitor of phenylalanine ammonia-lyase (PAL), a-aminooxy-{3-phenylpropionic acid (AOPP), only marginally increased growth of glyphosate-treated soybean seedlings (12). Thus, not all cases of glyphosate-caused growth inhibition or metabolic change can be explained solely in terms of glyphosate-inhibited aromatic amino acid synthesis.…”