Resilience of barley (Hordeum vulgare) plants upon exposure to tramadol: Implication for the root-associated bacterial community and the antioxidative plant defence system

Insufficiently treated reclaimed water can act as a source of contamination by introducing recalcitrant contaminants (e.g., pharmaceutical compounds) to various water bodies and/or agricultural soils after irrigation. Tramadol (TRD) is one of these pharmaceuticals that can be detected in influents and effluents of wastewater treatment plants, at dis-charge points as well as in surface waters in Europe. While the uptake of TRD by plants through irrigation water has been shown, plant responses towards this compound are still unclear. Therefore, this study aims to evaluate the effects of TRD on selected plant enzymes as well as on the root bacterial community structure. A hydroponic experiment was conducted to test the effects of TRD (100 & mu;g L-1 TRD) on barley plants, at two harvesting time points after treatment. Accumulation of TRD in root tissues over time was observed reaching concentrations of 111.74 and 138.39 & mu;g g-1 in total root FW after 12 and 24 days of exposure, respectively. Furthermore, noticeable inductions in guaiacol peroxidase (5.47-fold), catalase (1.83-fold) and glutathione S-transferase (3.23-and 2.09-fold) were recorded in roots of TRD-treated plants compared to controls after 24 days. A significant alteration in the beta diversity of root-associated bac-teria due to TRD treatment was observed. Three amplicon sequence variants assigned to Hydrogenophaga, U. Xanthobacteraceae and Pseudacidovorax were differentially abundant in TRD-treated compared to control plants at both harvesting time points. This study reveals the resilience of plants through the induction of the antioxidative system and changes in the root-associated bacterial community to cope with the TRD metabolization/detoxification process.

Automated summary

Insufficiently treated reclaimed water can introduce recalcitrant contaminants to water bodies and agricultural soils. This study focuses on the effects of the pharmaceutical compound, tramadol, on plant enzymes and root bacterial community structure. The results show that TRD accumulates in root tissues over time and induces changes in enzyme levels and bacterial diversity. The study reveals the resilience of plants and their ability to cope with the TRD metabolization process.