Sharma, Nisha (2019) Effects of Environmental Pollutants in Plants: Sulfadiazine and Perfluoroalkyl Substances. [Ph.D. thesis]
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Abstract (italian or english)
There are many chemical contaminants, which are extremely dangerous to humans, animals and plants. Among many, here in my study, I chose two man-made chemical pollutants (SDZ and PFAAs) which are widely used by human beings directly and indirectly.
Sulfadiazine (SDZ), belonging to the class of sulfonamides, is one of the most detected antibiotics in the agricultural soil. The effect of SDZ on the growth, changes in antioxidant metabolite content and enzyme activities related to oxidative stress were analyzed. Moreover, the proteome alterations in Arabidopsis thaliana roots in response to SDZ was examined using a combined iTRAQ-LC-MS/MS quantitative proteomics approach. A dose-dependent decrease in leaf biomass and root length was evidenced in response to SDZ. Increased malondialdehyde content at higher concentration (2 μM) of SDZ was observed compared to control. In total, 48 differentially abundant proteins related to stress/stimuli response followed by transcription and translation, metabolism, transport and other functions were identified.
Another category of the chemical pollutants was perfluoroalkyl acids (PFAAs), on which a large number of studies are ongoing due to its characteristics and harmful effects on humans, animals and plants. The young rooted cuttings of Salix L. species exposed to the PFAA mixture tended to show a decline in the growth rate after 2 days of treatment. Regarding photosynthesis, the gas exchange parameters were affected more than those related to chlorophyll fluorescence. A decreasing trend in the PFAA concentration in leaves with increasing carbon chain length was observed, whereas long-chain PFAAs showed higher concentrations in roots. Accordingly, the foliage to root concentration factor highlighted that PFAAs with shorter carbon chain length (C ≤ 7) translocated and accumulated relatively more in leaves compared to roots. The removal efficiency of individual PFAAs for leaves and roots were comparatively higher with S. eleagnos and S. purpurea than S. triandra, with mean removal values at the whole plant level ranging around 10 % of the amount initially spiked, suggesting their potential for phytoremediation of PFASs. It was clear that the contamination of PFAAs was toxic, they are accumulated by plants and could enter into the food chain of human beings in a plant-based diet, especially plants from a contaminated area. Considering this, the effect of PFAAs was also examined in maize, being one of the most cultivated and consumed food crops worldwide. Also, maize is a major crop in the Veneto region, which is one of the four major PFAAs contaminated sites in the world. The mixture of PFAAs at 100 μg/L had a significant reduction on the growth of maize plants, affecting the uptake of the nutrient solution. It also implies that PFAAs accumulating in such cereal crops is a potential entry point for PFAA into the human food chain with increased risks when grown in hotspot regions, like Veneto region in Italy.
Further, experiments were carried out to identify the different metabolites that were altered due to PFAAs treatment. To understand the effects of PFAAs on plant metabolome, A. thaliana was chosen as it is easy growing plant and is thus suitable for NMR-based metabolomic study. The metabolite fingerprint of the samples was provided by novel NMR technology called CMP NMR, an effective tool which was used to compare the PFAAs exposed sample with control. The overall results indicated that the annotated metabolites levels are not modified when plant seedlings are treated with PFOA, PFOS at the selected concentration. On the other hand, the mixture of the 11 PFAA showed a significant modification of Alanine and Glutamine levels with an increase of 30 and 10-fold compared with the control, respectively.
Results of this study demonstrated the phytotoxic effects of PFAS on plants and their potential to accumulate in plants and in turn emphasize their entry into our food chain. Thus, also imply the very pertinent need for stringent methodologies to screen PFAS in plant-based diet and regulatory policies on the use of these chemicals in general.
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