Abstract
Bialaphos, L-2-amino-4-[(hydroxy) (methyl) phosphinoyl] butyryl-L-alanyl-L-alanine, at a concentration of 0.3 to 3mM did not inhibit glutamine synthetase (L-glutamine: ammonia ligase (ADP), EC 6.3.1.2, GS) extracted from shoots of Japanese barnyard millet (Echinochloa utilis OHWI). However, low GS activity was observed in the shoots treated with bialaphos. On the other hand, L-2-amino-4-[(hydroxy) (methyl)phosphinoyl]butyric acid (L-AMPB), a metabolite of bialaphos, inhibited GS both after extraction and in the shoot. The results suggest that bialaphos was metabolized into L-AMPB in plants and inhibited GS. The quantitative analysis of free amino acids in the bialaphos treated shoots showed a remarkable decrease in glutamine content 48hr after the treatment. An exogenous application of glutamine increased the glutamine to some extent in the bialaphos-treated shoots, but did not antagonize bialaphos in the herbicidal activity. Thus, it appears that a decrease of glutamine content by the herbicide was not a main factor to induce the herbicidal activity.
