Development of a New Herbicide, Bialaphos

Abstract

Bialaphos, L-2-amino-4-[(hydroxy) (methyl)phosphinoyl] butyryl-L-alanyl-L-alanine, is a metabolite of Streptomyces hygroscopicus and the first herbicide produced by fermentation. Bialaphos acted on foliage and was effective against a wide range of weeds including perennials. Bialaphos was slower acting than paraquat, but faster than glyphosate. It controlled the regrowth of weeds longer than paraquat but shorter than glyphosate. Translocation of radioactivity in Rumex obtusifolius treated with 14C-bialaphos was observed autoradiographically. Bialaphos did not affect emergence nor growth of crops through soil. Therefore, bialaphos is expected to be used widely for arable land including nontillage cultivation. Growth inhibition of pollen tube of Camellia japonica was recovered by the addition of glutamine. The result suggested that glutamine synthetase (L-glutamine: ammonia ligase (ADP), EC 6.3. 1.2, GS) was inhibited in the pollen. Decrease of GS activity was observed in shoots of Echinochloa utilis OHWI treated with bialaphos. Decrease in glutamine content was observed in plant leaf treated with bialaphos, but it did not appear that the decrease was a main factor for the herbicidal activity. Ammonia content in plant leaf was observed to increase in four hr after the treatment and reached about 30 to 100 times higher than the control in 24 to 48hr. The accumulation was not momentary, but maintained until the death of the plant. The high correlation between free ammonia content and herbicidal activity indicated that the toxicity of accumulated ammonia is the primary factor of herbicidal activity of bialaphos. The ammonia accumulation is considered to be a particular action of bialaphos in plants. More extensive use of microbial metabolites is expected by the fact that bialaphos was developed as a herbicide.