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As one of the most toxic environmental pollutants, cadmium (Cd) has lastingly been considered to have negative influences on plant growth and productivity. Recently, increasing studies have shown that low level of Cd exposure could induce hormetic effect which benefits to plants. However, the underlying mechanisms of Cd-triggered hormesis are poorly understood. In this study, we found that Cd stress treatment showed a hormetic effect on peppermint and Cd treatment with 1.6 mg L -1 concertation manifested best stimulative effects. To explore the hormesis mechanisms of Cd treatment, comparative transcriptome analysis of peppermint young plants under low (1.6 mg L -1 ) and high (6.5 mg L -1 ) level of Cd exposure at 0 h, 24 h and 72 h were conducted. Twelve of differentially expressed genes (DEGs) were selected for qRT-PCR validation, and the expression results confirmed the credibility of transcriptome data. KEGG analysis of DEGs showed that the phenylpropanoid biosynthesis and photosynthesis were important under both low and high level of Cd treatments. Interestingly, GO and KEGG analysis of 99 DEGs specifically induced by low level of Cd treatment at 72 h indicated that these DEGs were mainly involved in the pathway of phenylpropanoid biosynthesis and their functions were associated with antioxidant activity. The expression pattern of those genes in the phenylpropanoid biosynthesis pathway and encoding antioxidant enzymes during 72 h of Cd exposure showed that low level of Cd treatment induced a continuation in the upward trend but high level of Cd treatment caused an inverted V-shape. The changes of physiological parameters during Cd exposure were highly consistent with gene expression pattern. These results strongly demonstrate that low level of Cd exposure constantly enhanced antioxidant activity of peppermint to avoid oxidative damages caused by Cd ion, while high level of Cd stress just induced a temporary increase in antioxidant activity which was insufficient to cope with lasting Cd toxicity. Overall, the results presented in this study shed a light on the underlying mechanisms of the Cd-mediated hormesis in plant. Moreover, our study provided a safe method for the efficient utilization of mild Cd-contaminated soil as peppermint is an important cash plant.

Hormesis, which describes the stimulatory effect of low doses of toxic substances on growth, is a well-known phenomenon in the plant and animal kingdoms. However, the mechanisms that are involved in this phenomenon are still poorly understood. We performed preliminary studies on corn coleoptile sections, which showed a positive correlation between the stimulation of growth by Cd or Pb and an increase in the auxin and H2O2 content in the coleoptile sections. Subsequently, we grew corn seedlings in hydroponic culture and tested a wide range of Cd or Pb concentrations in order to determine hormetic growth stimulation. In these seedlings the gas exchange and the chlorophyll a fluorescence, as well as the content of chlorophyll, flavonol, auxin and hydrogen peroxide, were measured. We found that during the hormetic stimulation of growth, the response of the photosynthetic apparatus to Cd and Pb differed significantly. While the application of Cd mostly caused a decrease in various photosynthetic parameters, the application of Pb stimulated some of them. Nevertheless, we discovered that the common features of the hormetic stimulation of shoot growth by heavy metals are an increase in the auxin and flavonol content and the maintenance of hydrogen peroxide at the same level as the control plants.

AIMS: Biochar affects the progress of plant diseases caused by soilborne pathogens, frequently featuring U-shaped biochar dose/disease response curves. This study tested this phenomenon in common bean (Phaseolus vulgaris L.) with several biochars. METHODS: Four biochars prepared from two feedstocks (eucalyptus wood and greenhouse wastes) each at 350 and 600 °C were tested on bean seedling growth and infection caused by Rhizoctonia solani at concentrations of 0–3 % by weight. Biochar direct toxicity to R. solani was quantified in vitro. RESULTS: In general, lower concentrations (≤1 %) of biochar suppressed damping-off, whereas higher concentrations (3 %) were ineffective at disease protection. Plant growth in the absence of the pathogen was generally improved at all doses by the four biochars. Maximum growth response (G-Rₘₐₓ) generally occurred at higher biochar doses than maximum disease reduction (D-Rₘₐₓ). Direct toxicity to the pathogen could not explain disease reduction. CONCLUSION: Inverted U-shaped biochar dose/plant growth and biochar dose/disease reduction curves are emerging as common patterns in biochar/crop/pathogen systems. Frequently, the inflection between growth promotion and suppression occurs at different doses than the inflection between disease suppression and promotion. We term this the “Shifted Rₘₐₓ-Effect”. As there is no simple rule-of-thumb for crop/soil/biochar/dose/pathogen combinations, the possible effects of biochar on plant pathogens should not be overlooked.

The aim of this study is to explore the impact of cadmium (Cd) and arsenic (As) stress on physiological indexes and Cd/As uptake ability of Miscanthus , including Miscanthus sacchariflorus A0104, Miscanthus sinensis C0424 and C0640. Cd and As concentration showed significant hormesis effects on some physiological indexes, such as chlorophyll content, net photosynthetic rate, and MDA content. Compared with control group, Cd uptake can be most greatly enhanced by above fourfold with 150 mg/kg Cd treatment. As uptake of A0104 was increased by 3 ~ 33 folds with 200 mg/kg As treatment, C0424 was increased by 7–12 folds with 100 mg/kg As treatment, while C0640 was increased 1 ~ 6 folds with 250 mg/kg As treatment. The results also showed that C0640 was relatively better for the Cd remediation in the high Cd concentration (150 mg/kg) contaminated soil, while A0104 and C0424 were relatively better for the As remediation in the high As concentration (100 ~ 200 mg/kg) contaminated soil. Additionally, significantly ( p  < 0.05) close correlations were found among physiological indexes (except MDA content), while physiological indexes showed no significant relationship with the heavy metal contents in root, stem, and leaf.

Both inhibitory and stimulatory (known as hormesis) effects of the sublethal flupyradifurone, a butenolide insecticide, on Myzus persicae Sulzer (Hemiptera: Aphididae) were investigated for incorporating it into integrated pest management (IPM). A leaf-dip bioassay showed that flupyradifurone was very toxic against adult M. persicae with a 48 h LC50 of 8.491 mg/L. Using the age-stage two-sex life table approach, we assessed the effects of LC25 of flupyradifurone on adult M. persicae and its progeny (F1 and F2). On the one hand, aphids exposed to flupyradifurone had significantly negative effects on the life history traits acrossing the generations, such as reduced the adult longevity and fecundity of F0, shortened the duration of third instar and fourth instar nymphs, preadult period and the pre-reproductive period of F1, and decreased the reproductive days and adult longevity of F2. On the other hand, stimulatory effects on the duration of pre-adult, adult reproductive days, and reproduction of F1 were observed in the flupyradifurone-treated aphids. Consistently with the stimulation on individual traits, a higher net reproductive rate (R0) of F1 and a shorter mean generation time (T) of F2 were observed in the flupyradifurone-treated aphids, although the other population parameters including the intrinsic rate of increase (r), finite rate of increase (λ) and T of F1 and R0, r and λ of F2 were not significantly affected. These results revealed that adult M. persicae exposed to sublethal concentration of flupyradifurone can induce hormetic effects on F1, and also cause negative effects on F2. Our results would be useful for assessing the overall effects of flupyradifurone on M. persicae and the hormetic effects should take into consideration when use flupyradifurone for control M. persicae.

Ligusticum sinense cv. Chuanxiong ( L. Chuanxiong ), one of the widely used traditional Chinese medicines (TCM), is currently facing the problem of excessive cadmium (Cd) content. This problem has significantly affected the quality and safety of L. Chuanxiong and become a vital factor restricting its clinical application and international trade development. Currently, to solve the problem of excessive Cd, it is essential to research the response mechanisms of L. Chuanxiong to Cd stress. However, there are few reports on its physiological and biochemical responses under Cd stress. In this study, we conducted the hydroponic experiment under 25 μM Cd stress, based on the Cd content of the genuine producing areas soil. The results showed that 25 μM Cd stress not only had no significant inhibitory effect on the growth of L. Chuanxiong seedlings but also significantly increased the chlorophyll a content (11.79%) and root activity (51.82%) compared with that of the control, which might be a hormesis effect. Further results showed that the absorption and assimilation of NH 4 + increased in seedlings under 25 μM Cd stress, which was associated with high photosynthetic pigments. Here, we initially hypothesized and confirmed that Cd exceedance in the root system of L. Chuanxiong was due to the thickening of the root cell wall, changes in the content of the cell wall components, and chelation of Cd by GSH. There was an increase in cell wall thickness (57.64 %) and a significant increase in cellulose (25.48%) content of roots under 25 μM Cd stress. In addition, L. Chuanxiong reduced oxidative stress caused by 25 μM Cd stress mainly through the GSH/GSSG cycle. Among them, GSH-Px (48.26%) and GR (42.64%) activities were significantly increased, thereby maintaining a high GSH/GSSG ratio. This study preliminarily reveals the response of  L. Chuanxiong to Cd stress and the mechanism of Cd enrichment . It provides a theoretical basis for solving the problem of Cd excessive in L. Chuanxiong . Graphical Abstract Physiological and biochemical mechanisms of L. Chuanxiong seedlings under Cd stress. Highlights 1. Under 25 μM Cd, it was the hormesis effect on the growth of L. Chuanxiong . 2. Seedlings increased the thickness of root cell wall to chelate and fixate Cd. 3. Seedlings enhanced NH 4 + absorption and assimilation, thereby increasing chlorophyll content. 4. Seedlings mainly reduced oxidative stress caused by Cd stress through the GSH/GSSG cycle.

Insecticide induced-hormesis is a bi-phasic phenomenon generally characterized by low-dose induction and high-dose inhibition. It has been linked to insect pest outbreaks and insecticide resistance, which have importance in the integrated pest management (IPM). In this paper, hormesis effects of four insecticides on demographic parameters and expression of genes associated with metabolic resistance were evaluated in a field collected population of the green peach aphid, Myzus persicae Sulzer. The bioassay results showed that imidacloprid was more toxic than acetamiprid, deltamethrin and lambda-cyhalothrin. After exposure to sublethal doses of acetamiprid and imidacloprid for four generations, significant prolonged nymphal duration and increased fecundity were observed. Subsequently, mean generation time ( T ) and gross reproductive rate ( GRR ) was significantly increased. Moreover, expression of CYP6CY3 gene associated with resistance to neonicotinoids was increased significantly compared to the control. For pyrethriods, across generation exposure to sublethal doses of lambda cyhalothrin and deltamethrin prolonged the immature development duration. However, the expression of E4 gene in M. persicase was decreased by deltamethrin exposure but increased by lambda cyhalothrin. Based on results, demographic fitness parameters were effected by hormetic dose and accompanied with detoxifying genes alteration, hence, which would be evaluated in developing optimized insect pest management strategies.

Most studies on cadmium (Cd) have focused on its toxicity at high concentrations, while its hormetic effects at low doses remain underexplored. Lettuce (Lactuca sativa L) is cultivated on a wide scale around the world, and its leaves continue to exhibit a high capacity for Cd accumulation at trace concentrations, thereby posing a significant threat to human health. This study investigated the role of foliar-applied zinc oxide nanoparticles (nZnO, 50 μmol l-1 and 100 μmol l-1) in mitigating low-dose cadmium (Cd) stress in lettuce. Exposure to 2.5 μmol L-1 Cd significantly enhanced lettuce growth, demonstrating a classic hormetic response. However, this growth stimulation was accompanied by Cd accumulation in leaves (4.45 mg kg-1 DW, 0.22 mg kg-1 FW), exceeding the FAO/WHO safety limit for edible vegetables (0.2 mg kg-1 FW). Foliar application of nZnO significantly reduced the levels of reactive oxygen species (ROS) and malondialdehyde (MDA) in lettuce. This was accompanied by increased activities of antioxidant enzymes and elevated endogenous hormone levels, which collectively contributed to enhanced lettuce growth. Furthermore, it was demonstrated that nZnO led to a substantial reduction in Cd accumulation in lettuce tissues. This reduction was attributed to an increase in total phenolic content and changes in the subcellular distribution and chemical forms of Cd. Our results indicate that foliar application of zinc oxide nanoparticles is a viable strategy for reducing Cd accumulation in lettuce and other leafy vegetables under Cd-induced hormesis, thereby ensuring food safety.

Hormesis is a dose–response phenomenon observed in numerous living organisms, caused by low levels of a large number of stressors, among which metal ions. In cities, metal levels are usually below toxicity limits for most plant species, however, it is of primary importance to understand whether urban metal pollution can threaten plant survival, or, conversely, be beneficial by triggering hormesis. The effects of Cd, Cr and Pb urban concentrations were tested in hydroponics on three annual plants, Cardamine hirsuta L. , Poa annua L. and Stellaria media (L.) Vill., commonly growing in cities. Results highlighted for the first time that average urban trace metal concentrations do not hinder plant growth but cause instead hormesis, leading to a considerable increase in plant performance (e.g., two to five-fold higher shoot biomass with Cd and Cr). The present findings, show that city habitats are more suitable for plants than previously assumed, and that what is generally considered to be detrimental to plants, such as trace metals, could instead be exactly the plus factor allowing urban plants to thrive.

The antiglycemic drug metformin, widely prescribed as first-line treatment of type II diabetes mellitus, has lifespan-extending properties. Precisely how this is achieved remains unclear. Via a quantitative proteomics approach using the model organism Caenorhabditis elegans , we gained molecular understanding of the physiological changes elicited by metformin exposure, including changes in branched-chain amino acid catabolism and cuticle maintenance. We show that metformin extends lifespan through the process of mitohormesis and propose a signaling cascade in which metformin-induced production of reactive oxygen species increases overall life expectancy. We further address an important issue in aging research, wherein so far, the key molecular link that translates the reactive oxygen species signal into a prolongevity cue remained elusive. We show that this beneficial signal of the mitohormetic pathway is propagated by the peroxiredoxin PRDX-2. Because of its evolutionary conservation, peroxiredoxin signaling might underlie a general principle of prolongevity signaling.