Enantioselective and synergistic herbicidal activities of common amino acids against Amaranthus tricolor and Echinochloa crus-galli

Abstract

Amino acids have a wide range of biological activities, which usually rely on the stereoiso-mer presented. In this study, glycine and 21 common α-amino acids were investigated for their herbicidal property against Chinese amaranth (Amaranthus tricolor L.) and barnyard grass (Echinochloa crus-galli (L.) Beauv.). Both D-and L-isomers, as well as a racemic mixture, were tested and found that most compounds barely inhibited germination but moderately suppressed seedling growth. Various ratios of D:L-mixture were studied and synergy between enantiomers was found. For Chinese amaranth, the most toxic D:L-mixtures were at 3:7 (for glutamine), 8:2 (for methionine), and 5:5 (for tryptophan). For barnyard grass, rac-glutamine was more toxic than the pure forms; however, D-tryptophan exhibited greater activity than racemate and L-isomer, indicating the sign of enantioselective toxicity. The mode of action was unclear, but D-tryptophan caused bleaching of leaves, indicating pigment synthesis of the grass was inhibited. The results highlighted the enan-tioselective and synergistic toxicity of some amino acids, which relied upon plant species, chemical structures, and concentrations. Overall, our finding clarifies the effect of stereoisomers, and provides a chemical clue of amino acid herbicides, which may be useful in the development of herbicides from natural substances.