Enantioselectivity and allelopathy both have effects on the inhibition of napropamide on Echinochloa crus-galli

Design, Synthesis, and Structure-Activity Relationship (SAR) Studies of Ketone-Isobenzofuranone Hybrid Herbicides

Thirty-five ketone-isobenzofuranone hybrids (1-35) were designed, synthesized, and evaluated for their herbicidal activity against Chinese amaranth (Amaranthus tricolor) and barnyard grass (Echinochloa crus-galli). The structure-activity relationship (SAR) results revealed that the position and type of substituent were crucial for activity. The o-substituted derivatives outperformed the m- and p-substituted derivatives. Compounds with strong electron-donating groups (OH, OMe) had low activity, while those with heterocycles (N-methylpyrrole, furan, and thiophene) had a moderate herbicidal effect. Compounds with a weak electron-donating group (Me) and weak, moderate, and strong electron-withdrawing groups (F, Cl, Br, and NO₂ ) showed promising herbicidal activity. Among these, the o-F substituted compound (20) was the most effective against Chinese amaranth, and the o-Cl substituted compound (23) was the most potent against barnyard grass. This is the first time the herbicidal potential of ketone-isobenzofuranone hybrids has been studied. The discovery of current chemical clues would be beneficial for the development of novel herbicides.

Enantioselectivity and mechanisms of chiral herbicide biodegradation in hydroponic systems

This study demonstrates the enantioselective removal dynamics and mechanisms of the chiral herbicide metolachlor in a hydroponic system of Phragmites australis. It presents the first work to elucidate plant-microbial driven enantioselective degradation processes of chiral chemicals. The results showed a degradation efficiency of up to 95.07 ± 2.81% in the hydroponic system driven by a notably high degradation rate constant of 0.086 d^-1. P. australis was demonstrated to rapidly increase the contribution of biodegradation pathways in the hydroponic system to 82.21 ± 4.81% within 4 d with an enantiomeric fraction (EF) drop to 0.26 ± 0.02 to favour the enantioselective degradation of S-Metolachlor (k_{S-Metolachlor} = 0.568 d^-1 and k_{R-Metolachlor} = 0.147 d^-1). Comparatively, the biodegradation pathways in the control constituted less than 25%, with an EF value of circa 0.5. However, the enantioselective biodegradation pathways exhibited complete reversal after about 4 d to favour R-Metolachlor. Plants promoted the degradation of R-Metolachlor, evidenced by an increase in EF to 0.59 ± 0.03. Nonetheless, metolachlor showed an inhibitory effect on plants reflected by the reduction of plant growth rate, chlorophyll content, and electron transport rate to -7.85 ± 1.52%, 1.33 ± 0.43 mg g^-1, 4.03 ± 1.33 μmol (m² s)^-1, respectively. However, rhizosphere microorganisms aided plants to catalyze excessive reactive oxygen species production by the antioxidant enzymes to protect plants from oxidative damage and restore their physiological activities. High-throughput analysis of microbial communities demonstrated the enrichment of Massilia (40.63%) and Pseudomonas (8.16%) in the initial stage to promote the rapid degradation of S-Metolachlor. By contrast, the proliferation of Brevundimonas (32.29%) and Pseudarthrobacter (11.03%) in the terminal stage was closely associated with the degradation of R-Metolachlor. Moreover, as symbiotic bacteria of plants, these bacteria aided plants protection from reactive oxygen damages and promoted the recovery of plant metabolic functions and photosynthesis. Overall, these results demonstrate biodegradation mediated by plant-microbe mechanisms as the main driver for the enantioselective degradation of metolachlor in hydroponic systems.

Enantioselective and Synergistic Herbicidal Activities of Common Amino Acids Against Amaranthus tricolor and Echinochloa crus-galli

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.