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The aim of the present study was to elucidate the role of oxidative stress in the mode of action of acetolactate synthase (ALS) inhibiting herbicides. Two populations of Amaranthus palmeri S. Watson from Spain (sensitive and resistant to nicosulfuron, due to mutated ALS) were grown hydroponically and treated with different rates of the ALS inhibitor nicosulfuron (one time and three times the field recommended rate). Seven days later, various oxidative stress markers were measured in the leaves: H2O2, MDA, ascorbate and glutathione contents, antioxidant enzyme activities and gene expression levels. Under control conditions, most of the analysed parameters were very similar between sensitive and resistant plants, meaning that resistance is not accompanied by a different basal oxidative metabolism. Nicosulfuron-treated sensitive plants died after a few weeks, while the resistant ones survived, independently of the rate. Seven days after herbicide application, the sensitive plants that had received the highest nicosulfuron rate showed an increase in H2O2 content, lipid peroxidation and antioxidant enzymatic activities, while resistant plants did not show these responses, meaning that oxidative stress is linked to ALS inhibition. A supralethal nicosulfuron rate was needed to induce a significant oxidative stress response in the sensitive population, providing evidence that the lethality elicited by ALS inhibitors is not entirely dependent on oxidative stress. This work was financed by the Public University of Navarre (Project UPNA20-6138) and the Spanish Ministry of Science and Innovation (2020 117723-RB-100). ME is the holder of a predoctoral fellowship of the Basque Government and he also received a mobility grant from the same Government. The authors would like to acknowledge G. Garijo, J. Encinas and C. Jiménez for technical assistance, and J. Torra (University of Lleida, CAT, Spain) for providing seeds.

We thank the Journal of Experimental Botany for supporting our research community and providing us with an opportunity to present the updates in this Special Issue.

Fonds Wetenschappelijk Onderzoek (FWO) SB-1S92022N

The Campine region in Flanders is well-known for its highly cadmium (Cd)-contaminated soils due to past anthropogenic activities. Enhanced Cd exposure can cause cellular damage in plants, and consequently reduces crop growth and plant quality (Jozefczak et al., 2014). Currently, few cost-effective and non-destructive remediation techniques exist (Tang and Ni, 2021). Therefore, alternative soil remediation techniques should be assessed. Biochar is a solid material that is produced by pyrolysis of biomass. Because of its functional surface, it can be used as a cost-effective adsorbent for various (in)organic pollutants in soils and waste waters (Sizmur et al., 2017). However, differences in biochar properties will affect their adsorption performance. Therefore, suitable biomass streams and biochar production conditions should be selected to increase adsorption efficiency. Biochars from eight biomass feedstocks (spent peat, green waste, chicken manure, coffee grounds, flax shives, insect frass, tree bark and apple wood) were subjected to pyrolysis at 450 and 600 °C (pilot-scale rotary kiln reactor) and evaluated for their Cd removal efficiency (CRE) in a buffered 2-(N-morpholino)ethanesulfonic acid (MES) solution (0.025 M Cd; pH = 6; 1:20 solid:liquid ratio) for ten days. The results show that CRE varied from 4 to 96 wt.% with the highest CRE by chicken manure biochars (94-96 wt.%). Insect frass biochar (produced at 450 °C) also had a high CRE (77 ± 4 wt.%). All the other biochars exhibited a CRE below 50 wt.%. A 10-day kinetic adsorption study in the MES solution was executed on four biochars (450 °C) (tree bark, spent peat, insect frass and chicken manure) due to their divergent adsorption performance. A 24-hr desorption step with 0.01 M Ca(NO3)2 was executed to investigate the leachability of the adsorbed Cd. Chicken manure biochar showed the fastest Cd removal rate with a removal of 93 ± 1 wt.% within one day, while the Cd removal of insect frass biochar started at 41 ± 2 wt.% and gradually increased to 77 ± 4 wt.%. Cd Leaching from the loaded biochar was limited (< 10 wt.%) but spent peat biochar leached approx. two times more Cd compared to chicken manure biochar. Future pot and large-scale plant growth experiments with these biochars will provide more insight on their performance in real-life scenarios. This will open new possibilities for the remediation of Cd-contaminated soils.

Due to human activities, soils become more and more polluted with metals, which imposes risks for human health and wildlife welfare. As most of the metals end up in the food chain through accumulation in plants, we need to establish science-based environmental criteria and risk management policies. To meet these necessities, a thorough understanding is required of how these metals accumulate in and affect plants. Many studies have been conducted towards this aim, but strikingly, only a few entries can be found in ecotoxicological databases, especially on Arabidopsis thaliana, which serves as a model species for plant (cell) physiology and genetic studies. As experimental conditions seem to vary considerably throughout literature, extrapolation or comparison of data is rather difficult or should be approached with caution. Furthermore, metal-polluted soils often contain more than one metal, yet limited studies investigated the impact of metal mixtures on plants. This review aims to compile all data concerning root system architecture under Cu, Cd and Zn stress, in single or multi-metal exposure in A. thaliana, and link it to metal-induced responses at different biological levels. Global incorporation into an adverse outcome pathway framework is presented. Fonds Wetenschappelijk Onderzoek, Grant/ Award Numbers: G0B6716N, G0C7518N, G0460.12; Universiteit Antwerpen, Grant/Award Number: Bijzonder Onderzoeksfonds (BOF); Universiteit Hasselt

Plants are phytochemical hubs containing antioxidants, essential for normal plant functioning and adaptation to environmental cues and delivering beneficial properties for human health. Therefore, knowledge on the antioxidant potential of different plant species and their nutraceutical and pharmaceutical properties is of utmost importance. Exploring this scientific research field provides fundamental clues on (1) plant stress responses and their adaptive evolution to harsh environmental conditions and (2) (new) natural antioxidants with a functional versatility to prevent and treat human pathologies. These natural antioxidants can be valorized via plant-derived foods and products. Cuba contains an enormously rich plant biodiversity harboring a great antioxidant potential. Besides opening new avenues for the implementation of sustainable agroecological practices in crop production, it will also contribute to new strategies to preserve plant biodiversity and simultaneously improve nature management policies in Cuba. This review provides an overview on the beneficial properties of antioxidants for plant protection and human health and is directed to the valorization of these plant antioxidants, emphasizing the need for biodiversity conservation. This research was funded by VLIR-IUC, grant number CU2019IUC030A105-77143 and VLIR-TEAM, grant number CU2017TEA433A102. Cuypers, A (corresponding author), Hasselt Univ, Ctr Environm Sci, Campus Diepenbeek,Agoralaan Bldg D, BE-3590 Diepenbeek, Belgium. Cos, P (corresponding author), Univ Antwerp, Lab Microbiol Parasitol & Hyg LMPH, Univ Pl 1, BE-2610 Antwerp, Belgium. gabriel@uo.edu.cu; daniel.mendez@reduc.edu.cu; sophie.hendrix@uhasselt.be; jcea@uo.edu.cu; yilan@uo.edu.cu; aochoap@uo.edu.cu; jgadi@uo.edu.cu; jquevedo@uo.edu.cu; albys@uo.edu.cu; elizabetha@uo.edu.cu; natalie.beenaerts@uhasselt.be; isidro.mendez@reduc.edu.cu; torbera@uo.edu.cu; paul.cos@uantwerpen.be; ann.cuypers@uhasselt.be

Frost stress severely affects agriculture and agroforestry worldwide. Although many studies about frost hardening and resistance have been published, most of them focused on the aboveground organs and only a minority specifically targets the roots. However, roots and aboveground tissues have different physiologies and stress response mechanisms. Climate models predict an increase in the magnitude and frequency of late-frost events, which, together with an observed loss of soil insulation, will greatly decrease plant primary production due to damage at the root level. Molecular and metabolic responses inducing root cold hardiness are complex. They involve a variety of processes related to modifications in cell wall composition, maintenance of the cellular homeostasis and the synthesis of primary and secondary metabolites. After a summary of the current climatic models, this review details the specificity of freezing stress at the root level and explores the strategies roots developed to cope with freezing stress. We then describe the level to which roots can be frost hardy, depending on their age, size category and species. After that, we compare the environmental signals inducing cold acclimation and frost hardening in the roots and aboveground organs. Subsequently, we discuss how roots sense cold at a cellular level and briefly describe the following signal transduction pathway, which leads to molecular and metabolic responses associated with frost hardening. Finally, the current options available to increase root frost tolerance are explored and promising lines of future research are discussed. Luxembourg National Research Fund (FNR) [project X-press AFR PhD/17/SR 11634190]

Additional file 2. Ecosystem services categorization.