Interaction between Phthalate Ester and Rice Plants: Novel Transformation Pathways and Metabolic-Network Perturbations

This work reveals whole transformationpathways and phytotoxicitymechanism of phthalate ester in rice and informs environmental risksand crop safety related to plasticizer pollution. Ourunderstanding is limited concerning the interaction mechanismbetween widespread phthalate esters and staple crops, which have strongimplications for human exposure. Therefore, this study was aimed atilluminating the transformation pathways of di-n-butylphthalate (DnBP) in rice using an untargeted screening method. UPLC-QTOF-MSidentified 16 intermediate transformation products formed throughhydroxylation, hydrolysis, and oxidation in phase I metabolism andfurther by conjugation with amino acids, glutathione, and carbohydratesin phase II metabolism. Mono-2-hydroxy-n-butyl phthalate-l-aspartic acid (MHBP-asp) and mono-2-hydroxy-n-butyl phthalate-d-alanyl-beta-d-glucoside (MHBP-ala-glu)products were observed for the first time. The proteomic analysisdemonstrated that DnBP upregulated the expression of rice proteinsassociated with transporter activity, antioxidant synthesis, and oxidativestress response and downregulated that of proteins involved in photosynthesis,photorespiration, chlorophyll binding, and mono-oxygenase activity.Molecular docking revealed that DnBP can affect protein molecularactivity via pi-sigma, pi-alkyl, and pi-pi interactionsor by forming carbon-hydrogen bonds. The metabolomic analysisshowed that key metabolic pathways including citrate cycle, biosynthesisof aminoacyl-tRNA, and metabolism of amino acids, sphingolipids, carbohydrates,nucleotides, and glutathione were activated in rice plants exposedto DnBP and its primary metabolite mono-n-butyl phthalate(MnBP). Furthermore, exposure to 80 ng/mL MnBP significantly perturbedthe metabolic profile and molecular function in plants, with downregulationof the levels of beta-alanine (0.56-fold), cytosine (0.48-fold), thymine(0.62-fold), uracil (0.48-fold), glucose (0.59-fold), and glucose-1-phosphate(0.33-fold), as well as upregulation of the levels of l-glutamicacid (2.97-fold), l-cystine (2.69-fold), and phytosphingosine(38.38-fold). Therefore, the degradation intermediates of DnBP posea potentially risk to plant metabolism and raise concerns for cropsafety related to plasticizer pollution.

Automated summary

This study reveals the transformation pathways and phytotoxicity mechanism of phthalate ester in rice, providing important information on environmental risks and crop safety related to plasticizer pollution. It identifies intermediate transformation products and proteins associated with different metabolic activities in rice plants exposed to di-n-butylphthalate (DnBP). Furthermore, it shows the perturbation of key metabolic pathways and molecular functions in plants exposed to its primary metabolite mono-n-butyl phthalate (MnBP). These findings highlight the potential risks posed by the degradation intermediates of DnBP and raise concerns for crop safety.