Abstract
Amino acids have a wide range of biological activities, which usually rely on the stereoisomer 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 enantioselective 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.
Highlights
It is well-known that to produce enough agricultural crops to feed the growing world population, farmers must rely on synthetic chemicals to eliminate pests and weeds
Synergistic Effects of D- and L-Amino Acids on Tested Plants. These results suggested that types of amino acids and isomers affected toxicity
The results indicated synergistic behavior between D-glutamine and L-glutamine
Summary
It is well-known that to produce enough agricultural crops to feed the growing world population, farmers must rely on synthetic chemicals to eliminate pests and weeds. These herbicides allow us to achieve high crop yields. These chemicals, when left behind in the environment, are usually toxic to plants, animals, or even humans. Recently, agricultural scientists are looking for a new approach for weed control [3,4,5]. Many chemists believe that alternative herbicides should be natural products [6,7]. This concept is widely accepted because of the long-standing belief that natural substances are relatively safer than synthetic compounds
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