Mecanismos de tolerância e alterações metabólicas em plantas de linhaça dourada (Linum usitatissimum L.) expostas e co-expostas a arsênio e selênio

Abstract

The goal of this work was to investigate the antagonistic and synergistic interactions between As and Se in golden flaxseed plants (Linum usitatissimum L.) in order to understand how Se changes the tolerance mechanisms and metabolism in the presence of As. Absorption, toxicity, translocation and the distribution of essential nutrients (Fe, Mn and Zn) in plants were evaluated in the experiments exposure to AsV, SeIV and SeVI and co-exposure to AsV + SeIV . Seedlings were cultivated in a 10 % v v-1 Hoagland solution supplemented with AsV, SeIV, SeVI or AsV + SeIV at different concentrations. Elemental quantification was performed by inductively coupled plasma mass spectrometry (ICP-MS). The changes caused by Se in the tolerance mechanisms and metabolism when co-exposed to As were also investigated using two mass spectrometry with ambient ionization techniques PS-MS (paper spray mass spectrometry) and DESI-MSI (desorption electrospray ionization mass spectrometry imaging). The detection and identification of thiolic compounds (phytochelatins and their metabolites) and inorganic and organic compounds of As and Se in extracts from co-exposed root plant were made by PS-MS. Metabolic changes caused in plant leaves exposed to AsV, SeIV and co-exposed to AsV + SeIV were verified by chemical images obtained by DESI-MSI. Exposure and co-exposure experiments demonstrated that SeVI was the most toxic species with the highest translocation by the plant. SeIV at a concentration of 5 µmol L-1 was able to reduce the accumulation of As and the co-exposure altered the absorption of Fe, Mn and Zn. The detection and identification of phytochelatins (PCs), that are thiolic compounds responsible for complexing metals and metalloids in plants and reducing their toxicity was possible using PS-MS. Glutathione (GSH), reduced-PC2, reduced-PC3, SeII-PC2 and AsIII-PC3 were identified in the extracts of co-exposed plants. Inorganic compounds (AsV and AsIII) and organic compounds (dimethylarsinic acid - DMA and monomethyarsonic acid - MMA) from As were also identified by PS-MS. In the leaves it was possible to verify four profiles of metabolic changes that occurred after exposure and co-exposure at different concentrations of As and Se. SeIV decreases AsV toxicity although As absorption and translocation have increased. It was not possible to associate the decrease in AsV toxicity in the presence of SeIV with the PCs formation. The most evident metabolic changes observed in the leaves indicated the formation of metabolites related to abiotic stress.