Enantioselection bioactivity disturbances in the photosynthesis of Echinochloa crus-galli caused by flusulfinam, a novel chiral herbicide

Flusulfinam is a novel chiral herbicide that exists in two stereoisomeric forms. The possible enantioselective effect on Echinochloa crus-galli remains unknown. R-flusulfinam was 7.13 and 1.69 times more active against E. crus-galli than S-flusulfinam and Rac-flusulfinam, respectively. R-flusulfinam caused impairment to the photosynthetic system of E. crus-galli and resulted in the disruption of photosynthetic pigmentation levels. A systematic analysis of the carotenoid fraction content was conducted utilizing liquid chromatography-tandem mass spectrometry. This was particularly noticeable with the decline in several carotenoids, including β-carotene, α-carotene, and lycopene. Furthermore, real-time fluorescence quantitative PCR was employed for gene expression analysis. Treatment with R-flusulfinam altered the gene expression profiles of E. crus-galli related to photosynthesis. Specifically, the expression levels of genes encoding photosynthetic reaction center components, such as PSAD, PSBS, and PETE, were changed. And a significant reduction in the transcription of genes involved in carotenoid biosynthesis, including PSY, PDS, and ZDS, was observed. Furthermore, hydrogen peroxide and malondialdehyde contents were determined as well as antioxidant enzymes (SOD, CAT, and POD) activity assays, R-flusulfinam treatment group exhibited a higher degree of oxidative damage to E. crus-galli. R-flusulfinam demonstrated greater herbicidal activity than S-flusulfinam by substantially inhibiting photosynthesis and inducing oxidative damage. These results contribute to understanding the potential enantioselective mechanisms of flusulfinam against E. crus-galli and provide evidence to support the application of enantiomerically pure R-flusulfinam to reduce the application rate of herbicides.