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As emerging persistent pollutants, microplastic (MPs) pollution attracted increasing attention worldwide since it is posing several environmental concerns. MPs interact with heavy metals in soil and may provoke damages on soil properties and ultimately impaired plants and human health. The present study aims to evaluate alfalfa plants (Medicago sativa) response after exposure to heavy metal polluted soils from mine site in the North of Tunisia in presence of environmental microplastic. For that, soils were sampled from two sites of Jebel Ressass mine in addition to a control soil. Plants were exposed to the three soils in presence of two increasing rates of microplastics D1 (1 mg/kg of soil) and D2 (100 mg/kg of soil) for 60 days. After harvest, agronomic parameters, chlorophyll content as well as heavy metal accumulation in plants were analyzed. Furthermore, oxidative status was evaluated in terms of malondialdehyde accumulation (MDA), catalase (CAT) activities and glutathion-S-transferase (GST). Overall, our finding highlights that MPs disrupted agronomic parameters and the photosynthetic activities of alfalfa plants. Additionally, our results revealed that the presence of MPs in polluted soils cause an increase on heavy metal accumulation in alfalfa shoots. Biochemical analyses demonstrated that the combined exposure to MPs and heavy metal induced oxidative stress in alfalfa plants by increasing CAT activity and MDA accumulation. The present investigation highlights the ecological risks of microplastics in terrestrial environment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Industrial wastes and fertilizers can introduce excessive levels of nickel (Ni) into the environment, potentially causing threats to plants, animals, as well as human beings. However, the number of studies on the effects of Ni toxicity on nodules is fairly limited. To address this issue, the effects of increasing Ni concentration on alfalfa nodules were assessed at chemical, biochemical, and transcriptomic levels. For this purpose, plants were grown in soils supplied with Ni (control, 0 mg/kg; C1, 50 mg/kg; C2, 150 mg/kg; C3, 250 mg/kg; and C4, 500 mg/kg) for 90 days. Ni loads in leaves, roots, and nodules were monitored after the exposure period. A set of biochemical biomarkers of oxidative stress was determined in nodules including antioxidants and metal homeostasis as well as lipid peroxidation. Gene expression levels of the main targets involved in oxidative stress and metal homeostasis were assessed. Our data indicated a high concentration of Ni in leaves, roots, and nodules where values reached 25.64 ± 3.04 mg/kg, 83.23 ± 5.16 mg/kg, and 125.71 ± 4.53 mg/kg in dry weight, respectively. Moreover, a significant increase in nodule biomass was observed in plants exposed to C4 in comparison to control treatment and percentage increased by 63%. Then, lipid peroxidation increased with a rate of 95% in nodules exposed to C4. Enzymatic activities were enhanced remarkably, suggesting the occurrence of oxidative stress, with increased superoxide dismutase (SOD), glutathione reductase (GR), and ascorbate peroxidase (APX). Our results showed also a significant upregulation of SOD, GR and APX genes in nodules. Nodule homoglutathione (HGSH) levels increased with the different Ni concentrations, with a remarkable decrease of glutathione S-transferase (GST) activity and glutathione (GSH) content for the highest Ni concentration with 43% and 52% reduction, respectively. The phytochelatin (PC) and metallothionein (MT) concentrations increased in nodules, which implied the triggering of a cellular protection mechanism for coping with Ni toxicity. The results suggested that Ni promotes a drastic oxidative stress in alfalfa nodules, yet the expression of MT and PC to reduce Ni toxicity could be used as Ni stress bioindicators. Our findings provide new insights into the central role of alfalfa nodules in limiting the harmful effects of soil pollution. Therefore, nodules co-expressing antioxidant enzymes may have high phytoremediation potential., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Metal accumulation in soil could lead to severe damage to plants, animals, and humans. The present work aims to evaluate the effects of nickel (Ni) exposure on Medicago sativa at physiological, biochemical, and transcriptomic levels. Plants were exposed to five increasing concentrations of Ni (0, 50, 150, 250, and 500 mg/kg) for 60 days. Agronomic parameters (fresh and dry matter) and chlorophyll content (Chl) were determined in an alfalfa plant. Chemical analyses were conducted, involving the determination of Ni loads in plants (roots and shoots). Moreover, malondialdehyde accumulation (MDA), glutathione-S-transferase (GST), and peroxidase activities, termed as oxidative stress biomarkers, were measured. The gene expression levels of Prx1C, GST, and phytochelatins (PCs) were determined at different nickel concentrations. Our results showed that Ni concentration in plants increased significantly along with Ni concentration in the soil. Regarding oxidative stress biomarkers, Ni contamination caused an increase in peroxidase and GST activities, with a remarkable accumulation of MDA, especially for the highest Ni concentration (500 mg/kg of Ni). Our data showed also a significant upregulation of Prx1C and GST genes in shoots and roots. The PCs' gene expression was significantly enhanced in response to the different nickel concentrations, suggesting their important role in Ni detoxification in alfalfa plants. Our data provided evidence about the clear toxicity of Ni, an often-underestimated trace element., (Copyright © 2020 Elsevier Ltd. All rights reserved.)