Dose-response Phenomenon Research Articles

Does Widespread Use of Hydroxychloroquine Reduce the Transmissibility of SARS-CoV-2 / COVID-19? An Ecological Correlational Study.

At the beginning of the coronavirus disease (COVID-19) pandemic, hydroxychloroquine (HCQ) was widely used as a possible antiviral agent. Current knowledge indicates that HCQ has little or no effect on individual clinical outcomes of COVID-19, but populational effects on disease transmissibility are still unknown. This study investigates the hypothesis that massive HCQ consumption by a population may contribute to reducing the transmissibility of SARS-CoV-2 and COVID-19 spread by reducing the viral load of infected individuals. Public database of seven states from Brazil in 2020 were assessed, before the start of COVID-19 vaccination. The daily values of the COVID-19 effective reproduction number (Rt) were obtained. Associations between Rt values and the proposed predictor variables (prevalence of COVID-19 as a marker of collective immunity; social isolation indices; consumption of HCQ) were tested using multiple linear regression analysis. In all seven states, consumption of HCQ was a significant negative predictor of Rt (β ranged from -0.295 to -0.502, p = 0.001). Furthermore, the mean derivative of Rt during the declining period of the COVID-19 incidence (the mean rate of variation) was also significantly negatively related to the mean HCQ consumption in that period (R2 = 0.895; β = -0.783; p = 0.011), meaning that the higher the HCQ consumption, the faster the decline of COVID-19 Rt. It suggests a dose-response phenomenon and a causal relationship in this association. The results of this study are compatible with the hypothesis that HCQ has small but significant in vivo antiviral effects that are able to reduce SARS-CoV-2 transmissibility at the populational level.

Hormesis Responses of Growth and Photosynthetic Characteristics in Lonicera japonica Thunb. to Cadmium Stress: Whether Electric Field Can Improve or Not?

"Hormesis" is considered a dose-response phenomenon mainly observed at hyperaccumulator plants under heavy metals stress. In this study, the effects of electric fields on hormesis responses in Lonicera japonica Thunb. under cadmium (Cd) treatments were investigated by assessing the plant growth and photosynthetic characteristics. Under Cd treatments without electric fields, the parameters of plant growth and photosynthetic characteristics increased significantly when exposed to 5 mg L-1 Cd, and decreased slightly when exposed to 25 mg L-1 Cd, showing an inverted U-shaped trend, which confirmed that low concentration Cd has a hormesis effect on L. japonica. Under electric fields, different voltages significantly promoted the inverted U-shaped trend of the hormesis effect on the plant, especially by 2 V cm-1 voltage. Under 2 V cm-1 voltage, the dry weight of the root and leaf biomass exposed to 5 mg L-1 Cd increased significantly by 38.38% and 42.14%, and the photosynthetic pigment contents and photosynthetic parameters were also increased significantly relative to the control, indicating that a suitable electric field provides better improvements for the hormesis responses of the plant under Cd treatments. The synergistic benefits of the 5 mg L-1 Cd and 2 V cm-1 electric field in terms of the enhanced hormesis responses of growth and photosynthetic characteristics could contribute to the promoted application of electro-phytotechnology.

Statistical modeling of hormesis quantities in inverted U-shaped dose-response relationships by reparameterization of a bilogistic model

Statistical procedures that allow quantitative determination of hormesis features are required for quantitative characterization of hormesis to provide information on the biphasic dose-response phenomenon and its variability. Only a direct estimate of individual effective doses in hormetic dose-response relationships is possible using prior extensions of the bilogistic model of Beckon and coworkers. This study presented further extensions of the model to determine the toxic potency and hormetic dose zone by estimating two effective doses simultaneously. In addition, the extended models allow for partitioning the hormetic dose zone through the dose of maximum stimulation. This study demonstrated a 4-step statistical modeling approach to quantify 20 hormesis quantities. The applicability and challenges of the mathematical procedures are discussed based on a few examples of hormetic dose-response relationships. The syntaxes for the analyses were provided as Appendix to demonstrate its implementation in SAS® statistical software. Given the variability of hormetic dose-responses generated from toxicological studies in many disciplines, the proposed approach cannot apply to all dose-response patterns. However, we hope the proposed extensions could provide versatile statistical tools for quantitatively exploring a variety of biphasic dose-response curves.

A Conserved Mechanism for Hormesis in Molecular Systems.

Hormesis refers to dose-response phenomena where low dose treatments elicit a response that is opposite the response observed at higher doses. Hormetic dose-response relationships have been observed throughout all of biology, but the underlying determinants of many reported hormetic dose-responses have not been identified. In this report, we describe a conserved mechanism for hormesis on the molecular level where low dose treatments enhance a response that becomes reduced at higher doses. The hormetic mechanism relies on the ability of protein homo-multimers to simultaneously interact with a substrate and a competitor on different subunits at low doses of competitor. In this case, hormesis can be observed if simultaneous binding of substrate and competitor enhances a response of the homo-multimer. We characterized this mechanism of hormesis in binding experiments that analyzed the interaction of homotrimeric proliferating cell nuclear antigen (PCNA) with uracil DNA glycosylase (UNG2) and a fluorescein-labeled peptide. Additionally, the basic features of this molecular mechanism appear to be conserved with at least two enzymes that are stimulated by low doses of inhibitor: dimeric BRAF and octameric glutamine synthetase 2 (GS2). Identifying such molecular mechanisms of hormesis may help explain specific hormetic responses of cells and organisms treated with exogenous compounds.

Phytochemicals Targeting Oxidative Stress, Interconnected Neuroinflammatory, and Neuroapoptotic Pathways Following Radiation.

The radiation for therapeutic purposes has shown positive effects in different contexts; however, it can increase the risk of many age-related and neurodegenerative diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and Parkinson's disease (PD). These different outcomes highlight a dose-response phenomenon called hormesis. Prevailing studies indicate that high doses of radiation could play several destructive roles in triggering oxidative stress, neuroapoptosis, and neuroinflammation in neurodegeneration. However, there is a lack of effective treatments in combating radiation-induced neurodegeneration, and the present drugs suffer from some drawbacks, including side effects and drug resistance. Among natural entities, polyphenols are suggested as multi-target agents affecting the dysregulated pathogenic mechanisms in neurodegenerative disease. This review discusses the destructive effects of radiation on the induction of neurodegenerative diseases by dysregulating oxidative stress, apoptosis, and inflammation. We also describe the promising effects of polyphenols and other candidate phytochemicals in preventing and treating radiation-induced neurodegenerative disorders, aiming to find novel/potential therapeutic compounds against such disorders.

Hormetic effect of amyloid-beta peptide in hippocampal synaptic plasticity and memory

Background: The term hormesis refers to a biphasic dose-response phenomenon characterized by low-dose stimulation and high-dose inhibition represented by a J-shaped or U-shaped curve, depending on the parameter measured (Calabrese and Baldwin, Hum Exp Toxicol, 2002). Indeed, several, if not all, physiological molecules (i.e. glutamate, glucocorticoids, nitric oxide) are likely to present a hormetic effect, exhibiting opposite effects at high or low concentrations. In the last few years, we have focused on amyloid-beta (A), a peptide widely known because it is produced in high amounts during Alzheimer’s disease (AD). A is considered a toxic fragment causing synaptic dysfunction and memory impairment (Selkoe, Science, 2002). However, the peptide is normally produced in the healthy brain and growing evidences indicate that it might have a physiologic function. Aim: Based on previous results showing that picomolar concentrations of A42 enhance synaptic plasticity and memory (Puzzo et al, J Neurosci, 2008) and that endogenous A is necessary for synaptic plasticity and memory (Puzzo et al, Ann Neurol, 2011), the aim of our study was to demonstrate the hormetic role of A in synaptic plasticity and memory. Methods: We used 3-month old wild type mice to analyze how synaptic plasticity, measured on hippocampal slices in vitro, and spatial reference memory were modified by treatment with different doses of A (from 2 pM to 20 μM). Results: We demonstrated that A has a hormetic effect (Puzzo et al, Neurobiol Aging, 2012) with low-doses (200 pM) stimulating synaptic plasticity and memory and high-doses (≥ 200 nM) inhibiting these processes. Conclusions: Our results suggest that, paradoxically, very low doses of A might serve to enhance memory at appropriate concentrations and conditions. These findings raise several issues when designing effective and safe approaches to AD therapy.

Neonicotinoid Exposures that Stimulate Predatory Stink Bug, Podisus maculiventris (Hemiptera: Pentatomidae), Reproduction Do Not Inhibit Its Behavior.

Exposure to sublethal amounts of pesticide can compromise life-history traits and behavior of natural enemies thereby reducing their effectiveness as predators. However, sublethal exposures to pesticides and other stressors may also stimulate insects, a dose-response phenomenon known as hormesis. We previously reported stimulatory effects on reproduction in the beneficial insect predator Podisus maculiventris (Say) (Hemiptera: Pentatomidae) following exposure to sublethal concentrations of imidacloprid. Here we examined whether these same treatments stimulated behavior and/or predation of P. maculiventris. Stimulation of some behaviors occurred at a reproductively hormetic concentration and two additional sublethal concentrations, depending upon bioassay design and sex. We observed no substantial inhibition of behavior or predation at a reproductively hormetic concentration, demonstrating that reproductive fitness in P. maculiventris may be stimulated without compromising behaviors important in its effectiveness as a natural enemy.

Seaweed liquid extracts induce hormetic growth responses in mung bean plants

Hormesis is a dose–response phenomenon that is characterized by stimulation at low doses and inhibition at high doses. Extensive evidence has accumulated showing the occurrence of hormesis in numerous plant species independent of physicochemical agents, and this phenomenon has become a target for achieving greater crop productivity. Biostimulants (i.e., elicitors) are agents that activate adaptive responses, moderately stimulate biological performance and aid plants in tolerating stress when applied at low doses that fall within the stimulatory zone of a dose–response curve. Biostimulants based on seaweed liquid extracts (SLEs) are widely known to exert great benefits in plants at very low doses. However, the consequences to plants when SLEs are applied at high doses remain underexplored. A dose–response study was performed on mung bean (Vigna radiata) seedlings by applying a wide range of SLE doses to evaluate growth stimulation patterns. While the application of SLEs at high concentrations mostly caused a decrease in various morphological parameters, the application of SLEs at low concentrations stimulated some of these. Nevertheless, common features of SLE stimulation were present. Mung bean shoot length, root length, and dry weight responded to the SLE concentrations in a hormetic manner. A biphasic dose–response confirmed the relationships between SLE dose and mung bean plant growth parameters, which were due to the properties of the constituents of the SLE of each seaweed species. The SLE growth stimulation pattern found in this study will contribute to the establishment of safe application doses. This paper provides a strong foundation for enhancing the research protocols of studies on the effects of SLEs on plant growth and supports incorporating hormesis into risk assessment practices in agriculture.

Progestogen-induced alterations and their ecological relevance in different embryonic and adult behaviours of an invertebrate model species, the great pond snail (Lymnaea stagnalis)

The presence of oral contraceptives (basically applying estrogens and/or progestogens) poses a challenge to animals living in aquatic ecosystems and reflects a rapidly growing concern worldwide. However, there is still a lack in knowledge about the behavioural effects induced by progestogens on the non-target species including molluscs. In the present study, environmental progestogen concentrations were summarised. Knowing this data, we exposed a well-established invertebrate model species, the great pond snail (Lymnaea stagnalis) to relevant equi-concentrations (1, 10, 100, and 500 ng L−1) of mixtures of four progestogens (progesterone, drospirenone, gestodene, levonorgestrel) for 21 days. Significant alterations were observed in the embryonic development time, heart rate, feeding, and gliding activities of the embryos as well as in the feeding and locomotion activity of the adult specimens. All of the mixtures accelerated the embryonic development time and the gliding activity. Furthermore, the 10, 100, and 500 ng L−1 mixtures increased the heart rate and feeding activity of the embryos. The 10, 100, and 500 ng L−1 mixtures affected the feeding activity as well as the 1, 10, and 100 ng L−1 mixtures influenced the locomotion of the adult specimens. The differences of these adult behaviours showed a biphasic response to the progestogen exposure; however, they changed approximately in the opposite way. In case of feeding activity, this dose-response phenomenon can be identified as a hormesis response. Based on the authors’ best knowledge, this is the first study to investigate the non-reproductive effects of progestogens occurring also in the environment on molluscan species. Our findings contribute to the global understanding of the effects of human progestogens, as these potential disruptors can influence the behavioural activities of non-target aquatic species. Future research should aim to understand the potential mechanisms (e.g., receptors, signal pathways) of progestogens induced behavioural alterations.

Unraveling the effects of light rare-earth element (Lanthanum (III)) on the efficacy of partial-nitritation process and its responsible functional genera

Lanthanum-(La(III)) concentration in water resources is increasing exponentially in recent years following its widespread use as farm inputs via crop fertilizer production. However, studies on the effects of La(III) on nitrogen conversion and its removal mechanisms are still unclear. Consequently, this study investigated the effects of La(III) on partial-nitritation-(PN) process performance and bacteria activities via sludge morphology, extracellular polymeric substance (EPS) composition, organic functional group changes, and microbial community structure. The study revealed hormesis condition within the PN batch assays upon La(III) dosage, thus, dose-response phenomenon exhibited sludge stimulation at low La(III) dosage and inhibition at high-dose. Scanning electron microscope-energy spectroscopy (SEM-EDX), confocal laser scanning microscope (CLSM), and Fourier transform infrared spectroscopy (FTIR) confirmed efficient removal of La(III) (96.76%–99.93%) was achieved with polysaccharide and polysaccharide-protein complex through biosorption and biosynthesis. 16S rRNA gene sequencing demonstrated that La(III) significantly promoted the abundance of Nitrosomonas and identified Aquamicrobium as the ammonia oxidizing bacteria with high tolerance to La(III). Furthermore, phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) further revealed metabolic detoxification as pathways where enzymatic reactions neutralized and solubilized toxins. This study unraveled a strategic approach and insight into how Nitrosomonas and other functional genera regulate and control their activities against La(III) toxicity and subsequently enhance the PN process.

Effects of humic acids on biotoxicity of tetracycline to microalgae Coelastrella sp.

The release of antibiotics into aquatic environments would induce adverse effects on organisms, so the environmental impact and fate of antibiotics must be paid close attention. In this paper, the effects of tetracycline on the growth of microalgae Coelastrella sp. in the presence of humic acids were investigated at various tetracycline concentrations ranging from 0.5 to 10 mg/L in Blue-Green medium, and the underlying mechanisms were also discussed. Results revealed that the microalgae growth showed a hormesis dose-response phenomenon under tetracycline stress with stimulation at low levels (≤2 mg/L) while inhibition at higher levels (>2 mg/L). More importantly, tetracycline biotoxicity to Coelastrella sp. decreased significantly due to the increase in humic acids concentration, as evidenced by the increased biomass, chlorophyll-a and total proteins contents, as well as the reduced oxidative stress response in Coelastrella sp. cells. The strong complexation between tetracycline and humic acids was responsible for the reduced tetracycline biotoxicity. These findings are helpful for better understanding the environmental risk of antibiotics in eutrophic waters.

A review of neuropsychiatric adverse events from topical ophthalmic brimonidine.

Brimonidine is a first-line topical medication for increased intraocular pressure and glaucoma which may be used alone or in conjunction with other topical therapies. Its structural and pharmacological comparabilities to clonidine give way to the hypothesis that it may cause neuropsychiatric side effects. The majority of case reports citing brimonidine toxicity, either for topical or peripheral exposure, include pediatric age groups but especially infants. Among the latter, a dose-response phenomenon is evident. Dose-response correlates have also been shown among adults. Case series and prospective double-blind treatment studies also give evidence for the occurrence of several central nervous system adverse reactions. Topical ophthalmic brimonidine use should be followed for the occurrence of neuropsychiatric disturbances generally, and enhanced vigilance should be maintained for at-risk populations.

The two faces of nanomaterials: A quantification of hormesis in algae and plants

The rapid progress in nanotechnology has dramatically promoted the application of engineered nanomaterials in numerous sectors. The wide application of nanomaterials and the potential accumulation in the environment sparked interest in studying the effects of nanomaterials on algae and plants. Hormesis is a dose response phenomenon characterized by a biphasic dose response with a low dose stimulation and a high dose inhibition. This paper quantifies for the first time nanomaterial-induced hormesis in algae and plants. Five hundred hormetic concentration-response relationships were mined from the published literature. The median maximum stimulatory response (MAX) was 123%, and commonly below 200%, of control response. It was also lower in algae than in plants, and occurred commonly at concentrations <100 mg L−1. The no-observed-adverse-effect-level (NOAEL) to MAX ratio was 2.4 for algae and 1.7 for plants, and the two distributions differed significantly. Ag nanoparticles induced higher MAX than TiO2 and ZnO nanoparticles. The MAX varied upon nanomaterial application methods, growth stage of application (seed versus vegetative), type of endpoint and time window. While nanomaterial size did not affect significantly the MAX, sizes ≤50 nm appeared to have lower NOAEL:MAX ratio than sizes ≥100 nm, suggesting higher risks from incorrect application. The mechanisms underlying nanomaterial-induced hormetic concentration responses are discussed. This paper provides a strong foundation for enhancing research protocols of studies on nanomaterial effects on algae and plants as well as for incorporating hormesis into the risk assessment practices.

The Nucleoshuttling of the ATM Protein: A Unified Model to Describe the Individual Response to High- and Low-Dose of Radiation?

The evaluation of radiation-induced (RI) risks is of medical, scientific, and societal interest. However, despite considerable efforts, there is neither consensual mechanistic models nor predictive assays for describing the three major RI effects, namely radiosensitivity, radiosusceptibility, and radiodegeneration. Interestingly, the ataxia telangiectasia mutated (ATM) protein is a major stress response factor involved in the DNA repair and signaling that appears upstream most of pathways involved in the three precited RI effects. The rate of the RI ATM nucleoshuttling (RIANS) was shown to be a good predictor of radiosensitivity. In the frame of the RIANS model, irradiation triggers the monomerization of cytoplasmic ATM dimers, which allows ATM monomers to diffuse in nucleus. The nuclear ATM monomers phosphorylate the H2AX histones, which triggers the recognition of DNA double-strand breaks and their repair. The RIANS model has made it possible to define three subgroups of radiosensitivity and provided a relevant explanation for the radiosensitivity observed in syndromes caused by mutated cytoplasmic proteins. Interestingly, hyper-radiosensitivity to a low dose and adaptive response phenomena may be also explained by the RIANS model. In this review, the relevance of the RIANS model to describe several features of the individual response to radiation was discussed.

Hormetic UV‐C seed treatments for the control of tomato diseases

Hormesis is a dose response phenomenon in which low, non‐damaging doses of a stressor bring about a positive response in the organism undergoing treatment. Evidence is provided here that hormetic UV‐C treatments of tomato seed can control disease caused by Botrytis cinerea, Fusarium oxysporum f. sp. lycopersici (FOL) and f. sp. radicis‐lycopersici (FORL) on tomato (Solanum lycopersicum). Treating seeds with a 4 kJ m−2 dose of UV‐C significantly reduced both the disease incidence and progression of B. cinerea, with approximately 10% reductions in both on cv. Shirley. Disease severity assays for FOL and FORL on cv. Moneymaker showed dose‐dependent responses: UV‐C treatments of 4 and 6 kJ m−2 significantly reduced the disease severity scores of FOL, whilst only the 6 kJ m−2 showed significant reductions for FORL. To determine the effects of treatment on germination and seedling growth, UV‐C doses of 4, 8 and 12 kJ m−2 were performed on cv. Shirley. No negative impacts on germination or seedling growth were observed for any of the treatments. However, the 8 kJ m−2 treatment showed significant biostimulation, with increases in seedling, root and hypocotyl dry weight of 11.4%, 23.1% and 12.0%, respectively, when compared to the control. Furthermore, significant increases in the root‐mass fraction (10.6%) and root:shoot ratio (13.1%) along with a decrease in shoot‐mass fraction (2.0%) indicates that the 8 kJ m−2 treatment stimulated root growth to the greatest extent. There was no effect on hypocotyl and primary root length or the number of lateral roots, indicating no adverse effects to basic root architecture or seedling growth.

Mild heat stress induces hormetic effects in protecting the primary culture of mouse prefrontal cerebrocortical neurons from neuropathological alterations

Hormesis is a dose response phenomenon of cells and organisms to various types of stressors. Mild stress stimulates prosurvival pathways and makes the cells adaptive to stressful conditions. It is a widely used fundamental dose-response phenomenon in many biomedical and toxicological sciences, radiation biology, health science etc. Mild heat stress is an easily applicable hormetic agent that exerts consistent results. In the present investigations mouse cerebrocortical prefrontal neurons from E17 mouse embryos were grown in the laboratory on poly-L-lysine coated glass cover slips. The cells from the mild heat stressed group were subjected to a hyperthermic stress of 38 °C for 30 min every alternate day (i.e. mild heat stress was repeated after 48 h) up to the sixth day. After completion of twenty four hours of the final i.e. third exposure of the mild heat stress, the neurons were fixed for the cytochemical studies of neurofibrillary tangles, senile plaques, lipofuscin granules and Nissl substance. There was highly significant decrease in the neuropathological alterations (viz. deposition of Neurofibrillary tangles, deposition of senile plaques, accumulation of Lipofuscin granules) in the neurons from the mild heat stressed group as compared to control. Moreover, the Nissl substance was significantly preserved in the mild heat stressed group as compared to control. The results indicate that the applied mild heat stress (38 °C for 30 min) exerts beneficial effects on the prefrontal cerebrocortical neurons by slowing down the neuropathological alterations, suggesting the hormetic effect of the mild heat stress.

Silver nanoparticle-induced hormesis of astroglioma cells: A Mu-2-related death-inducing protein-orchestrated modus operandi

Hormesis is a dose-response phenomenon that, when applied to nanomaterial-biological interactions, refers to growth stimulation at low doses and growth inhibition at high doses. MUDENG (Mu-2-related death-inducing gene, MuD) is involved in cell death signaling. Astrocytes, the major glial cell type in the central nervous system, are a major source of brain tumors. In this study, we investigated whether silver nanoparticles (AgNPs) induce hormesis in astroglioma cells and the possible involvement of MuD in AgNP-induced hormesis. AgNPs exhibited cytotoxic effects on cell proliferation in a dose-dependent manner and increased MuD expression was observed during AgNP-induced astroglioma hormesis. Studies using MuD-knockout cells and MuD siRNA transfection showed that MuD might influence cell viability upon AgNP treatment. In addition, apoptotic cell population and production of reactive oxygen species in the absence of MuD were significantly increased. The phosphorylation of two mitogen-activated protein kinases, p38 and extracellular signal-regulated kinase (ERK), but not c-Jun N-terminal kinases (JNK), was observed upon AgNP stimulation. In summary, AgNPs at low doses induced hormesis of human astroglioma cells, and MuD and p38/ERK mediators are involved in AgNP-induced astroglioma hormesis, resulting in beneficial effects from the cellular point of view.

Emission of volatile organic compounds from plants shows a biphasic pattern within an hormetic context

Biogenic volatile organic compounds (BVOCs) are released to the atmosphere from vegetation. BVOCs aid in maintaining ecosystem sustainability via a series of functions, however, VOCs can alter tropospheric photochemistry and negatively affect biological organisms at high concentrations. Due to their critical role in ecosystem and environmental sustainability, BVOCs receive particular attention by global change biologists. To understand how plant VOC emissions affect stress responses within a dose-response context, dose responses should be evaluated. This commentary collectively documents hormetic-like responses of plant-emitted VOCs to external stimuli. Hormesis is a generalizable biphasic dose response phenomenon where the response to low doses acts in an opposite way at high doses. These collective findings suggest that ecological implications of low-level stress that may alter BVOC emissions should be considered in future studies. This commentary promotes new insights into the interface between biological systems and environmental change that influence several parts of the globe, and provide a base for advancing hazard assessment testing strategies and protocols to provide decision makers with adequate data for generating environmental standards.

Hormesis and paradoxical effects of pea (Pisum sativum L.) parameters upon exposure to formaldehyde in a wide range of doses.

Formaldehyde is a widespread pollutant of soil near roads including agricultural lands. Non-monotonic changes (hormesis and paradoxical effects) in chlorophyll (Ch) and carotenoid (Car) contents, the lipid peroxidation (LP) rate in plant leaves and growth parameters (GP) of plants can be caused by various pollutants. Hormesis is a biphasic dose-response phenomenon, characterised by low-dose stimulation and high-dose inhibition. The remaining types of non-monotonic responses are classified as paradoxical effects. While most authors who have studied formaldehyde and plants considered gaseous exposure to shoots, the effect of this pollutant in soil solution has been poorly examined. Thus, we studied the non-monotonic changes in Ch and Car contents, LP rate and GP in pea (Pisum sativum L.) upon exposure to formaldehyde in solution, at a wide range of sublethal concentrations from 0.063 × 10-2 to 0.16 g L-1. With formaldehyde exposure, LP and Ch contents had paradoxical effects (triphasic and multiphase changes, accordingly), while Car level did not change and GP exhibited a hormetic response. The date showed that pea parameters display diverse types of non-monotonic responses upon exposure to the same formaldehyde concentrations. High pollutant concentrations (0.08-0.16 g L-1) increased LP and significantly decreased GP (to 2.3-2.5 times compared to the control), while the Ch content was increased. Lower concentrations (<0.08 g L-1) caused a moderate deviation in all parameters from the control (not more than 62%) for hormesis and paradoxical effects.

Hormetic Response by Silver Nanoparticles on In Vitro Multiplication of Sugarcane (Saccharum spp. Cv. Mex 69-290) Using a Temporary Immersion System.

Background:Hormesis is considered a dose–response phenomenon characterized by growth stimulation at low doses and inhibition at high doses. The hormetic response by silver nanoparticles (AgNPs) on in vitro multiplication of sugarcane was evaluated using a temporary immersion system.Methods:Sugarcane shoots were used as explants cultured in Murashige and Skoog medium with AgNPs at concentrations of 0, 25, 50, 100, and 200 mg/L. Shoot multiplication rate and length were used to determine hormetic response. Total content of phenolic compounds of sugarcane, mineral nutrition, and reactive oxygen species (ROS) was determined.Results:Results were presented as a dose–response curve. Stimulation phase growth was observed at 50 mg/L AgNPs, whereas inhibition phase was detected at 200 mg/L AgNPs. Mineral nutrient analysis showed changes in macronutrient and micronutrient contents due to the effect of AgNPs. Moreover, AgNPs induced ROS production and increased total phenolic content, with a dose-dependent effect.Conclusion:Results suggested that the production of ROS and mineral nutrition are key mechanisms of AgNP-induced hormesis and that phenolic accumulation was obtained as a response of the plant to stress produced by high doses of AgNPs. Therefore, small doses of AgNPs in the culture medium could be an efficient strategy for commercial micropropagation.