Sulfonamides impede duckweed growth by inducing an excessive accumulation of salicylic acid

Sulfonamides, owing to their therapeutic properties and cost-effectiveness, are widely employed in clinical settings and the animal husbandry industry. However, the misuse of these compounds has resulted in severe water pollution, thereby posing significant threats to the growth and development of aquatic plants such as duckweed. Our controlled experiments revealed that sulfonamide exposure disrupts the plasma membrane integrity in duckweed root tip cortex cells and inhibits the root growth. Utilizing ESI-HPLC-MS/MS, we identified that sulfonamide exposure elicits an immune response in duckweed, characterized by the generation of substantial amounts of salicylic acid (SA). The exogenous application of SA exacerbated the sulfonamide-induced growth inhibition, whereas the addition of the SA synthesis inhibitor 1-aminobenzotriazole (ABT) mitigated the stress induced by sulfonamides. A loss-of-function mutant of ICS1, a key enzyme in the SA biosynthesis pathway, exhibited complete insensitivity to sulfonamide exposure. Furthermore, transcription factors SARD1 and CBP60g, which regulate ICS1 gene expression, were induced by sulfonamides, and their double mutant showed insensitivity to sulfonamide exposure. Reactive oxygen species (ROS) detection indicated abnormal accumulation of ROS in duckweed roots under sulfonamide exposure, which is likely to induce SA synthesis. These findings suggest that sulfonamide-mediated growth inhibition in plants is dependent on the ICS1-catalyzed SA biosynthesis pathway, thereby enhancing our understanding of the effects and mechanisms of sulfonamide exposure on aquatic plants. • Sulfonamide exposure elicits an immune response in duckweed, characterized by the generation of substantial amounts of salicylic acid (SA). • The exogenous application of SA exacerbated the sulfonamide-induced growth inhibition, whereas the addition of the SA inhibitor 1-aminobenzotriazole (ABT) mitigated the stress induced by sulfonamides. • Sulfonamide exposure induces overexpression of ICS1 gene and its regulatory transcription factor SARD1 , CBP60g , WRKY28 . Genetic analysis using Arabidopsis mutants indicates that sulfonamide exposure induces SA accumulation through the ICS pathway. • DAB and NBT staining indicated abnormal accumulation of reactive oxygen species (ROS) in duckweed roots under sulfonamide exposure, which is likely to induce SA synthesis.