Chitosan/tripolyphosphate Nanoformulation Carrying Paraquat: Insights of its Enhanced Herbicidal Activity

Despite a wide range of possible applications of nanopesticides, the mechanisms involved in their enhanced action remain largely unknown. Understanding the interaction between nanopesticides and plants is crucial for evaluating their potential safety application. Using an experimental and theoretical approach, this study aimed to investigate the target effect of paraquat-loaded chitosan/tripolyphosphate nanoparticles (ca. 200 nm) on the photosystem I (PSI). Thus, the electrochemical analysis showed distinct electroactivity behaviour between the herbicide encapsulated and non-encapsulated. The amount of lipid peroxidation, photooxidizable P700 reaction centre content, and NADPH/NADP+ ratio levels were significantly decreased in spinach leaf tissue exposed to the nanoherbicide compared to the non-encapsulated herbicide. The data also revealed that nanoformulation might act promoting oxidative stress by changes observed on antioxidant enzymes. Also, the molecular docking results showed a preferential disposition of the herbicide paraquat and paraquat-tripolyphosphate complex (TPP:PQ) into the ligand domain close to FAD and Glu312. Due to the inhibitor's strategic position into the catalytic pocket, a model of electron-capture is proposed, where the herbicide disturbs the redox process NADP+NADPH by capturing electrons to reduce itself. Finally, our findings provide important insights that the redox behaviour of the paraquat may play a key role in the enhanced efficiency of nanoherbicides to the target binding site.